Volcanic and Magmatic Studies Group Annual Meeting 2013

School of Earth Sciences University of Bristol 7th-9th January 2013

Supported by The Mineralogical Society of Great Britain and Ireland; registered charity number 233706.

VMSG 2013 – Welcome

Welcome

Bristol Volcanology welcomes you to VMSG 2013! Volcanology research at Bristol spans a truly wide range, encompassing everything from fluid dynamics and volcano physics to magmatic petrology, geochemistry, and risk assessment. We are pleased to be welcoming over 230 delegates from the U.K. and abroad to this year’s conference. Following the success of VMSG 2012, we have maintained a two-and-a-half day format and have scheduled dedicated poster sessions throughout the day on Tuesday. Oral sessions were vastly oversubscribed, and over 70% of the received abstracts are presented as posters, so please use poster sessions as an opportunity to take in the majority of the presented research.

Bristol Earth Sciences

The University College Bristol was founded in 1876 and was the first university in the country to admit women on an equal basis to their male counterparts. King Edward VII approved the Charter creating the University of Bristol in 1909. Today the university comprises six faculties, with over 13,000 undergraduates and over 4000 postgraduates.

The School of Earth Sciences is located in the neo-Gothic Wills Memorial Building. Geology has been offered as a subject since 1876, when topics such as solid crust, minerals, volcanoes and the history of the Earth were taught. For two lectures a week for two terms, this would cost you a sum of £3 and 3 shillings. Today, the School has six highly active research groups studying such diverse topics as climate, seismology, palaeobiology, petrology and geochemistry, and geologic hazards.

Acknowledgments

The Organising Committee gratefully acknowledges the Mineralogical Society for running the online registration and financial aspects of the conference and the VMSG Committee for their support throughout the organisation of this meeting. Hazel Bunting of the Bristol University Conference Office assisted with the venue hire and was endlessly helpful in accommodating the large number of poster presentations. We also thank our supporters (as of early December), Springer, AWE, SciMed, Thermo Fisher, Oxford Instruments, and FEI, as well as the Clifton Hotels Group and the The Grand Hotel by Thistle for offering discounted rates to delegates. Lorraine Field of the British Geological Survey provided many of the images used in publicity materials. Thanks again to all members of the Bristol Volcanology Research Group who have contributed to the organisation of this meeting and are not named below. Finally, cheers to those of you whose abstracts required no reformatting – you are the true heroes of VMSG 2013.

The Organising Committee

Alison Rust, Kate Saunders, Rose Burden, Jonathan Hanson, Emma Johnson, Elena Melekhova, Jenny Riker, Anne Schöpa, and Susanne Skora.

1 We would like to thank the following organsiations for their kind support of VMSG 2013

2 Programme Overview

Monday 7th January Tuesday 8th January Wednesday 9th January

9:00

Research in Progress Physical Volcanology and General Presentations Lecture Theatre 1, (Session 1) Chemistry Building 10:00 Auditorium, Victoria Rooms

Coffee 11:00 VMSG AGM East Foyer, Chemistry Registration opens 11 am Coffee East Foyer, Chemistry Victoria Rooms Research in Progress and General Presentations (Session 2) 12:00 Poster Session A Victoria Rooms Lecture Theatre 1, Chemistry Building

13:00 Student Forum Lunch Victoria Rooms Lunch East Foyer, Chemistry

Japan IODP Project 14:00 Welcome Geophysics Lecture Theatre 1, Magma Storage and Poster Session B Chemistry Building Degassing (Session 1) Victoria Rooms Lecture Theatre 1, John Guest (Session 1) 15:00 Chemistry Building Coffee Lecture Theatre 1, Victoria Rooms Chemistry Building

VMSG Award Talk: Coffee Coffee East Foyer, Chemistry 16:00 Mike Branney East Foyer, Chemistry Behaviour of Giant Pyroclastic Density Currents: Deductions from Deposits John Guest (Session 2) Magma Storage and Lecture Theatre 1, Degassing (Session 2) Poster Session C Chemistry Building 17:00 Lecture Theatre 1, and Drinks Reception Closing remarks Chemistry Building Victoria Rooms

18:00

Public Lecture: Ellen Stofan Conference Dinner Mapping of Volcanic Terrains across 19:00 and Ceilidh the Solar System Wessex Suite @Bristol Science Centre The Grand Hotel by Thistle

3 VMSG 2013 – Conference Logistics

Venues and Registration

Conference activities will be split between two main venues – the Chemistry Building and the Victoria Rooms (please see campus map). The entrance to Chemistry can be accessed from Cantocks Close, off of Woodland Road at the rear of Wills Memorial Building. Directions to Lecture Theatre 1 will be clearly posted within the building. The entrance to the Victoria Rooms is at the intersection of Queens Road and Whiteladies Road, and a detailed map of the venue is included in this volume.

Registration will take place on Monday, January 7th, from 11:00 to 13:45 in the East Foyer of the Chemistry Building. For those arriving on Tuesday, we will also host a registration table at the entrance to the Victoria Rooms.

Information for Presenters

Oral presentations. All oral presentations (excepting the VMSG award talk) will be allotted 12 minutes, plus an additional 3 minutes for questions. Acceptable formats are Microsoft PowerPoint or Adobe PDF. Please bring your presentation on a USB memory stick to be uploaded at the end of the preceding session. Presenters in the first session on Monday, January 7th, please upload your talk on arrival. Presenters in the first morning sessions on Tuesday and Wednesday, please upload your talk after the final session of the previous day.

Poster presentations. Poster boards are portrait orientation and the maximum poster size is A0 (W × H = 84 cm × 119 cm). All posters should be on display throughout Tuesday. Presenters are requested to stand by their poster during their allocated poster session. Please note your poster number, as this refers to your poster board, and the letter of your poster session (A, B, C), which indicates the session time. This information can be found in the meeting programme in this volume.

Internet Access

Fast eduroam wireless internet is available for delegates from organisations participating in the eduroam federation. Internet access will also be available in all conference venues via the VisitorNet Wi-Fi service. VisitorNet passwords and connection instructions can be collected by delegates at registration. Please only request a VisitorNet password if you are from a non-eduroam institution.

Conference Dinner and Ceilidh

The conference dinner will take place at The Grand Hotel on Monday, January 7th. The Grand is roughly 10-15 minutes walk from the Chemistry Building (see campus map). The cash bar in the Wessex Suite will be open from 6:30 p.m. for drinks, and dinner will begin at 7:15 p.m., with a Ceilidh following the meal.

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Washington Guest House Clifton Hotel Wills The Rodney Memorial Building Chemistry Hotel January 7th and 9th Victoria Rooms (enter via Cantocks Close) January 8th The Grand Hotel (conference Berkeley Square Hotel dinner)

@Bristol Science Centre Victoria Rooms Floor Plan (Tuesday 8th January)

LECTURE ROOM G12 VICTORIA’S ROOM

Magma Storage and Physical Volcanology Degassing Posters Posters THEATRE BAR John Guest Posters (seating area)

STAGE AUDITORIUM Oral Presentations

Exhibitors RECITAL ROOM Geophysics Posters Research in Progress and General Presentations Information Posters PORTERS and Registration Desk

Main Entrance

Refreshment location (please use both locations)

6 VMSG 2013 – Food and Drink

Food and Drink

In addition to Monday night’s conference dinner, lunch will be provided for delegates on Tuesday and Wednesday, and we will host a drinks reception concurrent with Poster Session C on Tuesday evening. If you wish to venture out on your own, there are plenty of great places to eat and drink in Bristol. A thorough guide to a wide range of pubs, bars, and restuarants, including maps, is provided below. All are within 20 minutes walk of the conference venues.

Clifton Village

Restaurants 1. Clifton Sausage (7 Portland Street, BS8 4JA) – Good quality, locally sourced British dishes with sausages an obvious speciality. Party Menu; 2 courses for £15 or 3 for £19. 2. Pizza Provencale (29 Regent Street, BS8 4HR) – The best pizzas in Bristol (often shared). £8-13 for 12”, £12-18 for 16”. 3. The Thali Café (1 Regents Street, BS8 4HW) – Award-winning curries made with locally sourced ingredients and a modern British kitsch twist. Main course < £10.

Pubs 4. The White Lion (Sion Hill, BS8 4LD) – Part of the Avon Gorge Hotel, including a large heated beer terrace with spectacular views of the famous Clifton Suspension Bridge. 5. The Mall (The Mall, BS8 4JG) – Cask ales, a secluded secret garden and great pub food. 6. The Cori Tap (8 Sion Place, BS8 4AX) – Famous throughout Bristol for serving the exclusive and infamous Exhibition Cider. Intrigued? You should be, it can only be served in half-pints… 7. The Lansdown (8 Clifton Road, BS8 1AF) – Traditional Bristish pub with a large heated outdoor area.

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7 VMSG 2013 – Food and Drink

Park Street, Park Row, and The Harbourside

Restaurants 8. Jamie’s Italian (87-89 Park Street) – Housed in a stunning listed building Jamie Oliver’s signature restauarant serves rustic, Italian food in a relaxed, friendly environment. Mains £10- 20. 9. ZaZa Bazaar (Canon’s Road, BS1 5UH) – A huge all-you-can-eat world banquet catering for up to 1000 guests. Definitely a sight to behold! Dinner £15. 10. Bordeaux Quay (Canon’s Road, BS1 5UH) – Award-winning restaurant serving European food in a stunning harbourside setting. Brasserie Menu ~£10. 11. La Tomatina (2 Park Street, BS1 5HS) – A newly opened Spanish tapas restaurant drawing inspiration from the festival of the same name. £3-5 per tapas dish.

Pubs 12. Bristol Ram (32 Park Street, BS1 5JA) – Good size local pub with a range of ales and bitters. Also serves food. 13. The Woods (1 Park Street Avenue, BS1 5LQ) – A modern pub serving a wide range of drinks and cocktails in a vibrant environment with a buzzing atmosphere. 14. The Ship (8 Lower Park Row, BS1 5BJ) – A comfy, classic pub experience with a large variety of drinks on tap. 15. Zero Degrees (53 Colston Street, BS1 5BA) – Very good beers produced in the onsite microbrewery. They also do nice pizza’s. 16. White Harte (54-58 Park Row, BS1 5LH) – A ‘Scream’ pub with cheap food and drinks and offers-a-plenty. Popular with students.

Bars 17. Goldbrick House (69 Park Street, BS1 5PB) – A classy champagne and cocktail bar with highly knowledgable bar tenders catering to every taste. 18. The Apple (Welsh Back, BS1 4SB) – Situated on a boat, this cider bar has won many awards and serves up a range of approximately 40 different ciders and cider-related drinks.

Clubs Java (9 Park Street) – A cocktail bar and club with a reputation as a premium destination for the city’s trendy young professionals. Agora (55 Park Street) – Good for dancing after 2 a.m.

The Centre

Restaurants 19. Guiseppes (59 Baldwin Street, BS1 1QZ) – A delicious yet affordable, traditonal, family- owned Italian restaurant. Highly reccomended. Before 7PM: main + a drink £6.50, or 2 courses + a drink £11.95. 20. Pizza Express (35 Corn Street, BS1 1HT) – Standard chain pizza restaurant. Pizzas from £8.

8 VMSG 2013 – Food and Drink

Pubs 21. The Bank (8 John Street, BS1 2HR) – A fantastic pub with friendly staff hidden away in the city centre, yet conveniently close to the Conference Dinner venue! 22. Commercial Rooms (45 Corn Street, BS1 1HT) – A Wetherspoons pub, we need say no more. 23. Horts (49 Broad Street, BS1 2EP) – A few doors down from the Conference Dinner venue.

Bars 24. The Rummer (All Saints Lane, BS1 1JH) – Independent cocktail bar and restaurant within a listed building in Bristol’s Old City Quarter, holding over 400 premium spirits from around the globe. Ideal for a post-dinner whiskey… 25. Start the Bus (7-9 Baldwin Street, BS1 1RU) – A lively bar that often plays host to a variety of live music. Open late. 26. The Big Chill (15 Small Street, BS1 1DE) – Artistically creative, bright and cheery. This laid-back place is open late and caters for a variety of tastes.

15 21 14 23 8 13 16 26 17 22 20 24 12 19 25 11

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The Triangle (…and around)

Restaurants 27. Wagamama (63 Queens Road, BS8 1QL) – Japanese restaurant and Noodle Bar down the road from the Victoria Rooms. Mains ~£10. 28. Browns (38 Queens Road, BS8 1RE) – A stylish blend of modern and clasic dishes as well as post-work cocktail happy hours. Mains £10-20. 29. Racks (St. Pauls Road, BS8 1LX) – A friendly and cosmopolitan bar & kitchen literally behing the Victoria Rooms. Highly reccomended. Mains from £8.

9 VMSG 2013 – Food and Drink

30. Cosmo (30 Triangle West, BS8 1ET) – A large all-you-can eat Pan-Asian dinery. Dinner £13.

Pubs 31. The Eldon (6 Lower Clifton Hill, BS8 1BT) – Good beer and decent pub grub. 32. Quinton House (Park Place, BS8 1JW) – Old man pub with good ales and pork scratchings. Limited seating space. Not recommended for large groups. 33. Brass Pig (1 Triangle West, BS8 1EJ) – The traditional feel of a public house in a more modern (and large) setting. 34. The Hope & Anchor (38 Jacob's Wells Road, BS8 1DR) – An equal rival to The Eldon. 35. The Berkeley (15-19 Queens Road, BS8 1QE) – Another Wetherspoons, opposite the Earth Sciences Department.

Bars 36. Mbargo’s (38-40 Triangle West, BS8 1ER) – Consistently busy with students and locals alike, happy-hour prices and dodgy DJ’s till late. What more could you ask for? 37. Illusions (2 Byron Place, BS8 1JT) – A multi award winning magic bar with free live shows. 38. Hermanos (55 Queens Road, BS8 1QQ) – An independent, neighbourhood café-bar serving coffee and cake by day and beer, cocktails and fine wines by night.

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32 30 33 27 36 38 28 37 35

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10 VMSG 2013 – Meeting Programme

Programme Monday 7th January 11:00 – 13:45 Registration in the East foyer, Chemistry Building

Afternoon session: Lecture Theatre 1: Chemistry Building Please ensure that oral presentations are uploaded prior to the start of your session.

13:45 Welcoming remarks (S) denotes a student presentation Session: Magma, storage & degassing 1 Chaired by: Catherine Annen, University of Bristol

13:50 Keynote: Changing the metaphor – from magma chamber to magma reservoir Kathy Cashman & Guido Giordano 14:05 (S) Experimental constraints on coupled degassing and crystallisation at Mount St. Helens Jenny Riker, Jon Blundy, Alison Rust 14:20 Degassing regime of Hekla volcano in 2012 Evgenia Ilyinskaya, Alessandro Aiuppa, Bergur Bergsson, Thrainn Fridriksson, Audur Agla Oladottir, Finnbogi Oskarsson, Katharina Lechner, Richard Yeo, Gaetano Giudice 14:35 (S) Triple magma batches and a complex history of a monogenetic volcano: geochemical analysis of Mt. Rouse, Newer Volcanics Province, Australia. Julie Boyce, Ian Nicholls, Reid Keays, Patrick Hayman 14:50 (S) Assembling a super-eruption: linking magma accumulation and eruption timescales at Toba. David Budd, Val Troll, Ester Jolis, Frances Deegan, Vicki Smith, Martin Whitehouse, Chris Harris, Carmela Freda, David Hilton, Sæmundur Halldorsson 15:05 (S) Shallow storage of dacites beneath Uturuncu volcano, SW Bolivia Duncan Muir, Jon Blundy, Alison Rust 15:20 The behaviour of a volcanic system with two linked magma chambers Stephen Blake

15:35-16:05 Coffee: East Foyer, Chemistry Building Session: Magma, storage & degassing 2 Chaired by: Evgenia Iiyinskaya, British Geological Survey

16:05 Petrological Cannibalism – the chemical and textural consequences of pulsatory growth of magma bodies. Jon Blundy & Kathy Cashman 16:20 (S) Plagioclase as a recorder of magma-crust interaction beneath the Faroe Islands Börje Dahren, Val Troll, Abigail Barker, Fiona Meade, Carmela Freda, Paul Holm, Nina Søager 16:35 (S) A new model for granitic emplacement: the Newry Igneous Complex, Northern Ireland Paul Anderson, Carl Stevenson, Mark Cooper, Rob Ellam, Ian Meighan, Colm Hurley, John Reavy, James Inman, Dan Condon, Quentin Crowley. 16:50 (S) Reconstructing the emplacement of the Lago della Vacca complex, Adamello Batholith, Italy, through field observations, image analysis and AMS. Anne Schöpa, Catherine Annen, Jon Blundy, Michel de Saint-Blanquat, Patrick Launeau 17:05 (S) Slurry remobilisation in a layered mafic sill (Franklin LIP, Victoria Island, Artic Canada Ben Hayes, Jean Bédard, Johan Lissenberg, C.D. Beard. 17:20 (S) Crystal-melt relationships and the record of deep mixing and crystallisation in the AD 1783 Laki eruption, Iceland. David Neave, Emma Passmore, John Maclennan, Godfrey Fitton, Thor Thordarson

11 VMSG 2013 – Meeting Programme

17:35 Glacial loading probes mantle heterogeneity beneath Iceland John Maclennan, Kenneth W.W. Sims, Janne Blichert-Toft, Evelyn Mervine, Jurek Bluzstajn, Karl Grönvold

Please vacate the Chemistry Building promptly at the end of the last session. The cash bar at the Wessex Suite, The Grand by Thistle will be open from 6:30 pm for drinks. It is a 10-15 minute from the Chemistry Building and there are several pubs/bars along the way for a pre-dinner drink.

19:00 Conference Dinner and Ceilidh: Wessex Suite The Grand by Thistle, Broad Street, Bristol BS1 2EL (Please note the cost of the dinner is included in your conference registration)

Tuesday 8th January Morning session: Auditorium: Victoria Rooms Please ensure that oral presentations are uploaded prior to the start of your session.

Session: Research in Progress and general presentations 1 Chaired by: Susanne Skora, University of Bristol

9:00 Keynote: Mission Immiscible for two subduction components; evidence from Pagan Volcano, Mariana arc Yoshihiko Tamura, Osamu Ishizuka, Robert J. Stern, Akiko Nunokawa, Hiroshi Shukuno, Hiroshi Kawabata, Yuka Hirahara, Qing Chang, Takashi Miyazaki, Jun- Ichi Kimura, Robert W. Embley, Sherman Bloomer, Yoshiyuki Tatsumi 9:15 (S) Melting beneath the Izu volcanic arc: constraints from Uranium series isotopes Heye Freymuth, Tim Elliott, Yoshihiko Tamura 9:30 (S) Diatreme volcanism facilitating Pb-Zn mineralisation in the Irish Orefield? Holly Elliott, Tom Gernon, Stephen Roberts, Patrick Redmond 9:45 (S) The Comsos Greenstone terrane; Insights into a mineralised Archean Arc from U-Pb dating, volcanic stratigraphy and geochemistry Alexandra de Joux & Thor Thordarson

10:00 (S) Carbonatite genesis: An experimental approach in the CMASK-CO2 system Sorcha McMahon, Mike Walter, Ken Bailey 10:15 Rheology of Three-Phase magmas Mattia Pistone, Luca Caricchi, Peter Ulmer, Eric Reusser, Federica Marone, Luigi Burlini 10:30 (S) Disturbed 40Ar/39Ar ages in basalt lavas: Chemical and X-ray computed tomographic (CT) evidence for fluid/basalt chemical interaction Elizabeth Cramer, Sarah Sherlock, Kate Dobson, Alison Halton, Stephen Blake, Tiffany Barry, Peter Lee, Simon Kelley, David Jolley 10:45 Taking geology to the IMAX: 3D and 4D insight into geological processes using micro-CT Kate Dobson, Peter Lee, David Brown, Tim Tomkinson, Elizabeth Cramer, Sarah Sherlock, Chedtha Puncreobutr, Kristina Kareh 11:00 VMSG AGM Andy Saunders

11:15-11:45 Coffee: Recital Room and Lecture Room G12

Poster sessions: Recital Room, Lecture Room G12 and Victoria’s Room

11:45- 12:45 Poster Session A Magma, Storage and Degassing A (Lecture room, G12)) Geophysics A (Recital Room) Research in Progress and General presentations A (Recital Room)

12:45-13:45 Lunch: Recital Room and Lecture Room G12

12 VMSG 2013 – Meeting Programme

Japan IODP project 13:45 Ultra-deep drilling into arc crust Yoshihiko Tamura, Yoshiyuki Tatsumi, Osamu Ishizuka, Robert J. Stern, James B. Gill, Julien A. Pearce, Richard Arculus and others

14:00- 15:00 Poster Session B Physical Volcanology B (Victoria’s Room) Research in Progress and General presentations B (Recital Room) Magma, Storage and Degassing B (Lecture Room, G12)

15:00-15:30 Coffee: Recital Room and Lecture Room G12.

VMSG Award Talk: Auditorium: Victoria Rooms 15:30 Behaviour of giant pyroclastic density currents: deductions from deposits ! ! Mike Branney ! ! ! ! ! !

Supported by

16:30- 17:45 Poster Session C Geophysics C (Recital Room) Hermel Hempstead, December 10 2012

Physical Volcanology C (Victoria’s Room) John Guest (Lecture room, G12)

A wine reception will be served during this poster session form the Recital Room and Lecture Room G12.

Public Lecture: @Bristol, Harbourside, BS1 5DB MappingOBJECT: of Volcanic Supporting Terrains the across VMSG the 2013 Solar System Ellen Stofan Please note 100 places have been reserved for VMSG delegates. Tickets will be allocated on a first come, first served basis from the Information Desk.

Dear Organizer,Wednesday 9th January

Morning session: LectureWe would T likeheatre to support 1: Chemistry the VMSG Building 2013 award and meeting with a contribution of £ 700. Session: Physical VolcanologyRegards Chaired by: Mike Branney , University of Leicester Thermo Scientific Team 9:00 Buoyancy of plume-sourced ash clouds: implications for ash transport modelling Steve Sparks , R. Baines, Rose Burden, Sam Engwell, Andrew Hogg, Herbert Huppert, Chris Johnson, Jessica Kandlbauer, Jeremy Phillips, Mark Woodhouse 9:15 (S) The duration of volcanic eruptions: controls and forecasts Leanne Gunn, Stephen Blake, Chris Jones, Hazel Rymer 9:30 (S) Climate and carbon cycle response to the 1815 Tambora eruption: pre-industrial vs. future Earth system simulations. Jessica Kandlbauer, Peter Hopcroft, Steve Sparks, Paul Valdes

9:45 (S) Newly discovered components of magmatism from Santorini are revealed during

cryptotephra studies of marine cores. Christopher Satow, Emma Tomlinson, Paul Albert, Sarah Collins, Katharine Grant, Sabine Wulf, Luisa Ottolini, Eelco Rohling, Martin Menzies, Simon Blocklet, Vicki Smith, Christina Manning, John Lowe 10:00 (S) The nature and scale of lava-water-sediment interaction: an example from the Fife- Midlothian Basin, Kinghorn, eastern Scotland. Heather Rawcliffe, David Brown, Brian Bell

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Scientific Instruments Stafford House Hemel Hempstead +44 (0)1442 233555 www.thermofisher.com Boundary Way HP2 7GE +44 (0)1442 233667 fax United Kingdom

Thermo Fisher Scientific is the trading name of Thermo Electron Manufacturing Limited. Registered Office:19 Mercers Row, Cambridge, CB5 8BZ, United Kingdom Registered No.441506 VAT No.827900029

VMSG 2013 – Meeting Programme

10:15 Inclined Vulcanian explosions at Soufriere Hills Volcano: causes and consequences Paul Cole, Adam Stinton, Roderick Stewart, Henry Odbert 10:30 Assigning a volcano alert level: negotiating uncertainty, risk, and complexity in decision-making processes Carina Fearnley

10:45-11:15 Coffee: East Foyer, Chemistry Building

Session: Research in progress and general session 2 Chaired by: Lucy Porritt and Anthony Burnham, University of Bristol 11:15 Pyroclastic granulation in explosive volcanic eruptions Tom Gernon, Martin Wood, Richard Brown, Chris Medlin, Mark Tait, Thea Hincks 11:30 (S) Continental crust formation in the Southern Central Andes: new insights from O and Hf isotopes in zircon Rosie Jones, Linda Kirstein, Simone Kasemann, Bruno Dhuime, Tim Elliott, Vanesa Litvak 11:45 (S) Melting rocks with magma: Sediment pyrometamorphism as a tracer of magma flow localisation in sills and dykes Clayton Grove, Dougal Jerram, Richard Brown, Jon Gluyas 12:00 (S) MORB-like halogens in basalts of the Azores archipelago Lisa Jepson, Ray Burgess, Vera Fernandes, Chris Ballentine 12:15 (S) Entablature Anne Forbes, Steve Blake, Dave McGarvie, Hugh Tuffen 12:30 Dihedral angles as a proxy for crystallisation times in dolerites Marian Holness & Chris Richardson 12:45 Student Forum Chaired by the VMSG student representative

12:45-13:45 Lunch: East Foyer, Chemistry Building

Afternoon session: Lecture Theatre 1: Chemistry Building Session: Geophysics Chaired by: Andy Nowacki and Mark Woodhouse, University of Bristol 13:45 The onset and evolution of pit crater collapse: insights from events at Pu’u O’o, Hawaii in 2011 Eoghan Holohan, Thomas Walter, Martin Schöpfer, John Walsh, Tim Orr, Mike Poland 14:00 (S) Structures of the rift zone in northern Iceland Sion Hughes & Hazel Rymer 14:15 (S) Volcanic unrest in Kenya: a satellite perspective Elspeth Robertson, Juliet Biggs, Marie Edmonds, Charlotte Vye-Brown 14:30 Magmatic systems within sedimentary basins Nick Schofield, Simon Holford, David Jolley

Session: John Guest Chaired by: Chris Kilburn, UCL 14:45 A tribute to John Guest Chris Kilburn 15:00 Contrasting lava flow dynamics and morphologies on planetary bodies Lionel Wilson 15:15 (S) The evolution of volcanism in Syrtis Major Planum (Mars): drawing insight from terrestrial analogues Peter Fawdon, Matt Balm, Charlotte Vye-Brown, Dave Rothery, Colm Jordan

15:30 – 16:00 Coffee: East Foyer, Chemistry Building

14 VMSG 2013 – Meeting Programme

Session: John Guest Chaired by: Chris Kilburn, UCL 16:00 Mapping of volcanic terrains across the Solar System Ellen Stofan 16:15 Pulsatory andesite lava flow at Bagana Volcano Geoff Wadge, Steve Saunders, Ima Itikarai 16:45 John Guest’s legacy on Mt. Etna: a spreading volcano with no chamber John Murray

17:00 Closing remarks Andy Saunders, VMSG Chair

Poster Contributions Posters should be displayed throughout the day on Tuesday. Posters have been arranged alphabetically per session. Please note the number of your poster as this refers to your poster board and the letter of your Poster Session (A, B, C). Poster sessions for particular themes have been spilt across Poster Sessions to enable easy access to all posters and to facilitate interaction between researchers. Please be present at your poster during the appropriate session.

Magma, storage & degassing: Posters 1-40, Lecture Room G12 Research in progress and general presentations: Posters 41-64, Recital Room Geophysics: Posters 65-86, Recital Room Physical Volcanology: Posters 87-113, Victoria’s Room John Guest: Posters 114-119, Lecture Room G12

Magma, storage & degassing (Lecture Room G12)

1_A (S) Geochemistry of Quaternary magmatism in the Greater Caucasus Samuel Bewick, Nigel Harris, Ian Parkinson, S. Adamia 2_B Eruption chemistry recorded by accretionary lapilli within pyroclastic density current deposits, Kilchrist, Isle of Skye, NW Scotland. David Brown, Simon Drake, Andrew Beard 3_A Long-term deformation at Uturuncu volcano in Bolivia and igneous diapirism in the crust Rodrigo del Potro, Mikel Díez, Cyril Muller, Jo Gottsman 4_B Geochemical and petrological analysis of products from the 2011 eruption of Nabro volcano, Eritrea Amy Donovan, Iris Buisman, Clive Oppenheimer 5_A Magma plumbing and degassing during the 2008-present summit eruption of Kilauea Volcano, Hawai’i Marie Edmonds, Tamsin Mather, Rob Martin, Isobel Sides, Richard Herd, Don Swanson 6_B Re-evaluating ‘super’ volcanoes: the case of Yellowstone Ben Ellis, Darren Mark, Michael Rowe, Olivier Bachmann 7_A (S) Hydrothermal cells and the Thermal Boundary Layer around the Cuillin Gabbro, Isle of Skye Fran Entwistle, Bruce Yardley, Adrian Boyce 8_B 2011-2012 eruption of Nyamuragira Marco Fazio, Adrian Jones, Andy Beard 9_A Petrological constraints on deep degassing prior to large basaltic fissure

eruptions: CO2 in Laki melt inclusions Margaret Hartley, John Maclennan, Marie Edmonds, Thor Thordarsson, Dan Morgan 10_B (S) Silicic volcanism in the Main Ethiopian Rift: A case study of Alutu Volcano William Hutchison, Juliet Biggs, Tamsin Mather, David Pyle, Gezahegn Yirgu 11_A (S) Modelling of magmatic hydrothermal systems: Phlegrean Fields case study Alia Jasim, Fiona Whitaker, Alison Rust

15 VMSG 2013 – Meeting Programme

12_B Magma mixing, storage and degassing during the 1959 Kilauea Iki eruption, Hawai’i Isobel Sides, Marie Edmonds, John Maclennan, Bruce Houghton, Don Swanson 13_A (S) Post-caldera explosive activity at Furnas volcano, São Miguel, Azores Adam Jeffery, Ralf Gertisser, Brian O’ Driscoll, A. Pimental, José Manuel Pacheco, Stephen Self 14_B (S) Compositional heterogeneity of the Earth’s convecting mantle: constraints from olivine-hosted melt inclusions from a continental flood basalt setting Eleanor Jennings, Sally Gibson, John Maclennan, Robert Thompson 15_A Tracking changes of magma transfer beneath Mt. Etna: Evidence from crystal zonation and real-time gas monitoring Maren Kahl, Sumit Chakraborty, Fidel Costa, Massimo Pompilio, Marco Liuzzo, Marco Viccaro 16_B (S) Timescales of magmatic processes at Mt. Ruapehu, New Zealand: linking mineral diffusion rates to monitoring data. Geoff Kilgour, Kate Saunders, Jon Blundy, Heidy Mader 17_A (S) Disequilibrium during volcanic eruption: effect of cooling rate on plagioclase- liquid element exchange Marthe Klöcking, Marie Edmonds, Madeleine Humphreys 18_B Melting events in the Rum layered intrusion Julien Leuthold, Jon Blundy, Marian Holness 19_A (S) The origin of the Igwisi Hills Kimberlite (Tanzania) constrained from He and O isotopes Freya Marks, Finlay Stuart, Richard Brown

20_B (S) An integrated study of SO2 degassing from Tungurahua volcano, Ecuador Brendan McCormick, Jian Yang, Marie Edmonds, Tamsin Mather, Simon Carn, Silvana Hidalgo, Baerbel Langmann, Michael Herzog 21_A (S) (Mis)understanding bubble growth in magma: Evidence from preserved volatile concentration gradients in glass Iona McIntosh, Ed Llewellin, Madeleine Humphreys, Alain Burgisser, Ian Schipper, Alex Nichols 22_B Granitoid magmatism during continental rifting: preliminary insights from the Oslo Rift, Norway Claire McLeod, Alan Brandon, Reidar Trønnes, Tom Lapen 23_A (S) Norwegian Larvikites: Colours & origin: An oxygen isotope study Ian Meighan, Tony Fallick, Rob Ellam 24_B Exploring volcanic-plutonic connections Vali Memeti & Jon Davidson 25_A (S) Magma storage and differentiation beneath Dabbahu Volcano, Afar, Ethiopia Hilary Milroy, Catherine Annen, Jon Blundy 26_B (S) Constraining the pre-eruptive storage conditions for Pollara eruptions of Salina, Italy Helena Moretti, Jo Gottsman, R. Sulpizio, Jon Blundy 27_A (S) Making granites in the BPIP: How did the evolved rocks in Centre 3, Ardnamurchan form? Joanne Murray, Fiona Meade, Rob Ellam, Val Troll 28_B (S) Degassing of sulphur from sediments in the Siberian Traps Large Igneous Province Svetlana Novikova, Christine Yallup, Marie Edmonds, Alexandra Turchyn, John Maclennan, Henrik Svensen 29_A The post-Minoan plumbing system behaviour at Santorini Volcanic Field: implications for the current unrest phase Chiara Maria Petrone, Lorella Francalanci, George Vougioukalakis 30_B (S) Geochemical evidence for relict degassing pathways in andesite Melissa Plail, Marie Edmonds, Madeleine Humphreys, Jenni Barclay, Richard Herd 31_A (S) Textural variations of groundmass microlites in the 2006 and 2010 eruptive products of Merapi volcano, Indonesia: evidence for magma ascent and shallow conduit processes. Katie Preece, Jenni Barclay, Ralf Gertisser, Richard Herd

16 VMSG 2013 – Meeting Programme

32_B (S) Reconciling sulphur dioxide emissions from satellite data with petrological volatile data for explosive eruptions of Mount Etna, Italy Lois Salem, Marie Edmonds, Brendan McCormick, Simon Carn 33_A (S) Effects of shear strain on deformation and degassing of three-phase magmas Jessie Shields, Luca Caricchi, David Floess, Heidy Mader, Mattia Pistone

34_B Effect of fO2 on phase relations and sulphur mobility during magmatic differentiation of a basaltic andesite Susanne Skora & Jon Blundy 35_A (S) Timescales of upper crustal residence at Campi Flegrei, Italy Vicki Smith, Kate Saunders, Roberto Isaia 36_B Triggering of major volcanic eruptions recorded by actively forming cumulates on Tenerife Michael Stock, Rex Taylor, Thomas Gernon 37_A The Alpehué Eruption, Sollipulli Caldera, Southern Chile Karen Strehlow, Armin Freundt, Steffen Kutterolf, Julie Christin Schindlbeck 38_B Evidence for an open magma system feeding the compositionally diverse Laacher See (Germany) eruption Emma Tomlinson, Vicki Smith, Martin Menzies 39_A (S) What lies beneath? A Sr and Pb isotope study of intrusive rocks on the Isle of Mull Marie Turnbull, Fiona Meade, G.R. Nicoll, Rob Ellam, Val Troll 40_B (S) Degassing of sulphur from shale adjacent to a dolerite sill in Skye: implications for the volatile budget of large igneous provinces Christine Yallup, Marie Edmonds, Alexandra Turchyn

Research in Progress and general presentations (Recital Room)

41_A (S) MORB like noble gas signatures within Western Antarctic Rift Zone Michael Broadley, Chris Ballentine, Ray Burgess 42_B The Snap Lake Kimberlite; A true composite intrusion Richard Brooker, Rachael Ogilvie-Harris, Tom Gernon, Steve Sparks, Matthew Field 43_A (S) Vesiculation of a rhyolitic melt: new insights from hot-stage microscopy experiments John Browning, Hugh Tuffen, Mike James 44_B Trace element systematics of zircon from I- and S-type granites Anthony Burnham, Andrew Berry, Ian Williams, Ryan Ickert 45_A (S) A tale of two magmas: Petrological insights into mafic and intermediate explosive volcanism at Volcán de Colima, Mexico Julia Crummy, Ivan Savov, Daniel Morgan, Marjorie Wilson, Carlos Navarro- Ochoa, Sue Loughlin 46_B Dynamics of deforming partially molten regions and the nucleation of dykes Mikel Diez, Jon Blundy, Andrew Hogg 47_A (S) The Red Hills intrusive system: Easternmost porphyry copper deposit in southwestern North America Amy Gilmer & Richard Kyle 48_B (S) The structure and evolution of shallow magmatic systems emplaces in fold-and- thrust belts – a case study of Cerro Negro, Neuquén Province, Argentina Derya Gürer, Fernando Corfu, Olivier Galland 49_A (S) Water/Rock interaction and volcanic behaviour Brioch Hemmings, Alia Jasim, Fiona Whitaker, Ben Buse, Jo Gottsmann 50_B (S) Experimental insights into the formation of amphibole reaction rims: Texture, mineralogy, and processes of formation Sarah Henton De Angelis, Jessica Larsen, Michelle Coombs, A. Dunn 51_A (S) Changes in heavy metal distribution and deposition at Poás Volcano, Costa Rica Melanie Hinrichs, Hazel Rymer, Steve Blake, Mike Gillman 52_B (S) Platitnum group element geochemistry of the Scourie Dykes: Insights ito the Lewisian subcontinental lithospheric mantle Hannah S.R. Hughes, Iain McDonald, Andrew Kerr

17 VMSG 2013 – Meeting Programme

53_B Fe3+/ΣFe in hydrous glass Madeleine Humphreys, Richard Brooker, Don Fraser, Vicki Smith 54_A Depositional and textural characteristics of “dry” maar volcanoes in northern Tanzania Hannes Mattsson 55_A (S) Temporal geochemical changes in the Miocene Ignimbrite succession on Gran Canaria: crustal contamination or mantle heterogeneity? Peter Nicholls, Val Troll, Ben Ellis, Abigail Barker, IIya Bindeman 56_B The source of A-type magmas in two contrasting settings: constraints on processes and tectonics from U-Pb, Lu-Hf and Re-Os isotopes. Matthew Pankhurst, Bruce Schaefer, Simon Turner 57_A Sm-Nd and U-Pb isotope geochemistry of the Sweetwater Wash and North Piute plutons, Mojave Desert, California. Stacy Phillips, John Hanchar, Calvin Miller 58_B The lattice strain model applied to coexisting garnet and cpx. Joe Pickles, Jon Blundy, Chris Smith 59_A (S) The role of ice cavities in lave lobe formation Hannah Reynolds, Duncan Woodcock, Jennie Gilbert, Steve Lane 60_B (S) Phreatomagmatic edifices produced by lava-sediment interaction Peter Reynolds, Rich Brown, Ed Llewellin, Thor Thordarsson, Kevin Fielding 61_A (S) Concentrations of critical metals in the Carnmenellis biotite granite, Cornwall, UK Bethany Simons, Jens Andersen, Robin Shail 62_B The nature of deep mantle from Afar plume picrites Finlay Stuart, Nick Rogers, Ian Parkinson, Heather Davies 63_A (S) Recognising mush disaggregation in basaltic systems: The distribution of olivine compositions in Icelandic basalts and picrites Andrew Thomson & John Maclennan

Geophysics (Recital Room)

65_A (S) Loading, compaction and injection: investigating ground deformation on Mt. Etna’s northeast crater flowfield Alistair Davies 66_C (S) Detection and categorization of geyser eruption dynamics: insights from infrasound monitoring at Yellowstone National Park Philippa Demonte, Jeffery Johnson, Aida Quezada-Reyes 67_A On the lack of InSAR measurements of deformation at Central American Volcanoes Susanna Ebmeier, Juliet Biggs, Tamsin Mather 68_C Hydroacoustic, infrasonic and seismic monitoring of the submarine eruptive activity and subaerial plume generation at South Sarigan May 2010 David Green, Läslo Evers, David Fee, Robin Matoza, Mirjam Snellen, Pieter Smets, Dick Simons 69_A (S) Crustal deformation between volcanic segments of the Askja and Kverkjöll central volcanoes, Northern Iceland Robert Green, Robert White, Tim Greenfield, Jon Tarasewicz, Heidi Soosalu, Janet Key 70_C (S) Local earthquake tomographic imaging of a magma chamber beneath Askja volcano, Iceland Tim Greenfield, Robert Green, Janet Key, Hilary Martens, Michael Mitchell, Robert White 71_C (S) Large-scale ground deformation at Uturuncu volcano: evidence for magma rise from the Altiplano-Puna magma body James Hickey, Jo Gottsmann, Rodrigo del Potro 72_A (S) A comparison of seismically imaged hydrothermal vents with field and laboratory analogues Murray Hoggett, Nick Schofield, Stephen Jones

18 VMSG 2013 – Meeting Programme

73_C (S) Anatomy of the onset of the current repose period at Volcán de Colima during July 2011 Oliver Lamb, Nick Varley, Tamsin Mather, David Pyle 74_A Modes of volcano growth and linkages to sub-volcanic intrusions determined using seismic reflection data from the Ceduna Sub-basin (offshore S Australia) Craig Magee, Esther Hunt-Stewart, Christopher Jackson 75_C (S) Sill geometries in 3D seismic data: Implications for sill emplacement Ben Manton & J. Cartwright 76_A (S) Causes of continuous activity at Arenal volcano, Costa Rica: preliminary results from a volcano-tectonic study Cyril Muller, Rodrigo del Potro, Jo Gottsmann, Juliet Biggs, Mikel Diez, Marino Protti, Gerardo Soto, Waldo Taylor 77_C ARGOS: Geophysical study of Alutu Andy Nowacki, Mike Kendall, Ian Bastow, Matthew Wilks, Juliet Biggs, Atalay Ayele, Shimeles Fisseha, Elias Lewi, Will Hutchison, David Pyle, Friedemann Samrock, Alexei Kuvshinov, Andy Jackson 78_A (S) Seismic and acoustics indices using the registered energies on Tungurahua volcano, Ecuador Pablo Palacios, Heidy Mather, Mike Kendall 79_C (S) Monitoring Cascade volcanoes using InSAR Amy Parker, Juliet Biggs, Tim Wright, Zhong Lu 80_A (S) A photogrammetric feasibility study for DEMs of gulleys in Ecuador Jacqueline Ratner, David Pyle, Tamsin Mather 81_C (S) Decreases in LP seismicity before the May 2011 eruption of the persistently restless Telica Volcano, Nicaragua Mel Rodgers, Halldor Geirsson, Molly Witter, Diana Roman, Peter LaFemina, Angelica Muñoz, Virginia Tenorio 82_A Geodetic data shed light on on-going caldera subsidence at Askja, Iceland Hazel Rymer & Elske de Zeeuw-van Dalfsen 83_C (S) Locating the source of volcanic noise, a picture tells a thousand hertz Elizabeth Swanson, Scase Mathew, David Green 84_A (S) Examining seismic precursors to eruptions at volcanoes in extensional stress fields using an experimental approach Richard Wall, Chris Kilburn, Philip Meredith 85_C (S) Digital mapping of accommodation structures associated with emplacement of the Maiden Creek intrusion, Henry Mountains, Utah Penelope Wilson, Ken McCaffrey, Robert Holdsworth, Jon Davidson, Pamela Murphy 86_A Comparing predictions of an integral model with observations of the Eyjafjallajökull 2010 plume Mark Woodhouse, L. Dowson, Jeremy Phillips

Physical Volcanology (Victoria’s Room)

87_B Dispersal and timing of major eruptive events at Ischia (Italy), insights from distal tephra records Paul Albert, Emma Tomlinson, Lucia Civetta, Sabine Wulf, Richard Brown, Vicki Smith, Giovanni Orsi, Christine Lane, Martin Menzies 88_C (S) Does volcanology work? Evidence from volcanic fatalities record Mel Auker, Steve Sparks, Lee Siebert, Sian Crosweller, J. Ewert 89_B (S) A glimpse into the future – Earth Science on trial! Richard Bretton, Jo Gottsmann, R. Christie 90_C (S) The structure and emplacement of the Rocche Rosse obsidian lava flow, Aeolian Islands, Italy Liam Bullock, Ralf Gertisser, Brian O’ Driscoll 91_B (S) A statistical method for determining the volume of volcanic fall deposits Rose Burden, Li Chen, Jeremy Phillips

19 VMSG 2013 – Meeting Programme

92_C (S) Ecological impacts of degassing and deposition from recent activity at Volcán Turrialba, Costa Rica Bethan Burson, Rob Martin 93_B Advances in the construction of volcanic records from marine sediment cores: A review and case study (Montserrat, West Indies) Michael Cassidy, Jess Trofimovs, Martin Palmer, W. Symons 94_C (S) Landslide processes at Montserrat, Lesser Antilles, and their implications for tsunami generation Maya Coussens, Peter Talling, Sebastian Watt, Mike Cassidy, Marin Palmer 95_B Interactions between mitigation strategies: implications for the scientific bases of mitigation policy Simon Day & Carina Fearnley 96_C (S) Eruption and depositional facies of the Stob na Doire Ignimbrite Member, Glencoe, NW Scotland: fault-bounded rheomorphic/lava-like and eutaxitic ignimbrite Jonathan Dietz, David Brown, Ross Dymock 97_B (S) Bentonised silicic pyroclastic fall deposits at the base of the Palaeogene Skye Lava Field which possess welded ignimbrite like fabrics Simon Drake & Andrew Beard 98_C (S) The importance of conduit erosion Jonathan Hanson, Alison Rust, M. Pavier, Jeremy Phillips 99_B Modelling disaster risk scenarios at La Soufrière, Guadeloupe Susanna Jenkins, Robin Spence, Peter Baxter, Jean-Christophe Komorowski, Sara Barsotti, Tomaso Esposti-Ongaro, Augusto Neri 100_C (S) Revised estimates for the volume of the Minoan eruption Emma Johnston, Steve Sparks, Jeremy Phillips 101_B (S) Stratigraphy and eruption history of peralkaline welded ignimbrites, Island of Pantelleria, Italy Nina Jordan, Rebecca Williams, Mike Branney, Mike Norry 102_C (S) Drilling into a super-eruption caldera? Initial report of the proximal rhyolites revealed by the Snake River deep drill hole, Idaho Tom Knott, Mike Branney, Marc Reichow, Mike McCurry & the HOTSPOT team 103_B (S) Glacial modulation of eruptive activity at Volcán Sollipulli, Chile Stefan Lachowycz, David Pyle, Tamsin Mather, Katy Mee, J. Naranjo 104_C Development of a database of volcanic ash layers from ocean drilling cores as a record of global explosive volcanism Sue Mahony, Steve Sparks, N. Barnard 105_B (S) Lithofacies architecture of the Stallachan Dubba Ignimbrite Member, Ardnamurchan, NW Scotland: valley-filling ignimbrites and the incursion of pyroclastic density currents into a lake Charlotte McLean, John Buchanan, Peter Reynolds, Peter Nicholls, Ross Dymock, Caroline Patmore, David Brown 106_C (S) The respiratory health hazard of volcanic ash: factors affecting the formation and toxicity of cristobalite Claire Nattrass & Claire Horwell 107_B (S) Exploring the mechanisms of basaltic fragmentation: insights from textural analysis Emma Nicholson, Kathy Cashman, Alison Rust 108_C Deforming a volcano by surface deposit loading: how loading may mislead classic deformation analyses Henry Odbert, Benoit Taisne, Steve Tait 109_B Pele’s tears and spheres – insights into the fragmentation of low viscosity magmas Lucy Porritt, James Russell, Steve Quane 110_C (S) The atmospheric habit of fine volcanic ash Gemma Prata, Benjamin Reed, Tamsin Mather, David Pyle, Dan Peters 111_B (S) The Sky’s the limit: mapping volcano deposits using kites Jonathan Stone, Jenni Barclay, Paul Cole, Sue Loughlin, Peter Simmons

20 VMSG 2013 – Meeting Programme

112_B Causes and effects of variations in groundwater inflows in a Stombolian to phreatomagmatic explosive eruption: the Cova de Paúl Crater eruption on Santo Antão, Cape Verde Islands. Bob Tarff & Simon Day 113_C Towards quantifying the arc-scale and global magmatic response to deglaciation Sebastian Watt, David Pyle, Tamsin Mather

John Guest (Lecture Room, G12)

114_C (S) Constraints on the physical characteristics of volcanic activity on Venus Martin Airey, Tamsin Mather, David Pyle 115_C Effusive activity at Somma-Vesuvius: lava flow-field characteristics from 1631 to 1944 Sarah Brown, Carmen Solana, Chris Kilburn 116_C (S) Lava channel networks Hannah Dietterich & Kathy Cashman 117_C (S) Kalkarindji – The forgotten volcanic province Peter Marshall & Mike Widdowson 118_C Levee control on the evolution of lava flow fields Marie Nolan, Carmen Solana, Chris Kilburn 119_C Inflation, drainage and lava-water interaction during the emplacement of the Nesjahraun, Iceland John Stevenson, Neil Mitchell, Mike Cassidy, Harry Pinkerton

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VMSG 2013 Presentation Abstracts

Oral and poster presentation abstracts are presented in the same order as in the meeting programme. A complete delegate list follows the abstracts.

23 VMSG 2013 – Oral Presentation Abstracts

Changing the metaphor – from Experimental constraints on magma chamber to magma coupled degassing and reservoir crystallisation at Mount St. Helens

K.V. CASHMAN*1, G. GIORDANO2 J.M. RIKER*1, J.D. BLUNDY1, A.C. RUST1 1 School of Earth Sciences, University of Bristol, UK. 1 School of Earth Sciences, University of Bristol, UK. (*[email protected]) (*[email protected]) 2 Dipartimento di Scienze Geologiche, Univ. Roma Tre, IT. Degassing and concomitant crystallisation play a major A long-lived conceptual model for pre-eruptive magma role in modulating the chemical and physical properties of storage envisions long-lived “magma chambers”, or large erupting magmas. Although the compositions and textures coherent bodies of magma (with or without included of natural volcanic rocks give evidence of varied and crystals). However, this model is difficult to reconcile with complex degassing histories, a limited experimental thermal models that suggest that large coherent volumes of framework exists within which to interpret such eruptible magma should represent transients within the observations. To address this problem, we present results of crust, and with new data showing that erupted magma a series of isothermal experiments on a synthetic Mount St. batches may be assembled shortly prior to eruption. Mafic Helens rhyodacite saturated with H2O and H2O-CO2 fluids. explosive caldera-forming eruptions are particularly Our runs simulate equilibrium crystallisation driven by difficult to explain by conventional models, because storage volatile exsolution at depths between a mid-crustal magma of large melt volumes is thermally implausible and storage region and the near-surface (400–25 MPa). Fluid vapour explosive ejection of large volumes of low vesicular magma compositions range from XH2O 0.4 to 1.0, as estimated cannot be viewed as solely gas-driven. To explain these from measured glass H2O and CO2 contents using a eruptions, we suggest instead melt storage within, and compositionally-dependent solubility model. Within this eruptions directly from, magma “reservoirs”, where we use parameter space, the stability of all phases (plagioclase, the term reservoir in the sense used for water-, oil- and gas- amphibole, orthopyroxene, Fe-Ti oxides, and rarer apatite bearing systems, that is, as pockets of liquid contained and silica) varies as a function of both pressure and fluid within a rigid framework, where here the framework is a composition, such that phase assemblages and proportions largely solidified magma body. This model extends the depend strongly on melt H2O content. Similarly, glass concept of eruptible melt assembled from a rigid sponge to compositions (69–78 wt% SiO2), plagioclase anorthite the idea that the sponge itself may feed eruptions. Tapping content (An52–An33), and total crystallinity (0–44 wt%) can an over-pressured network of melt pockets within a rigid be parameterised as simple functions of pH2O using data crystal framework provides an attractive model for several derived from experimental run products. Such reasons: (1) it does not require a large (thermally and parameterisations provide a context for comparing the physically unstable) body of molten magma to be assembled compositional and textural evolution of magmas subject to prior to an eruption, but instead allows erupted magma to be different gas transport scenarios, including closed-system stored within a thermodynamically stable crystal mush; (2) degassing, isobaric vapour fluxing, and vapour-buffered it allows syn-eruption tapping of large melt volumes from ascent. For each scenario examined, we evaluate the extent within the reservoir through permeable networks established to which magmas evolve along crystallisation trajectories both prior to and during eruption; (3) decompression of an that are distinct from one another and from the simpler case over-pressured reservoir provides a physical mechanism for of water-saturated ascent. A preliminary suite of dynamic magma ascent and eruption that does not rely on ascent- decompression experiments provides a counterpoint to the related gas exsolution as the only driving force; and (4) a equilibrium case. Our results demonstrate the potential of reservoir model can link the timing of caldera collapse erupted products to reveal information about the directly to the strength of the reservoir framework. We then composition, quantity, and transport of gases in magmatic speculate on the extent to which a magma reservoir model systems. They also underscore the importance of coupled may explain more general aspects of caldera formation. degassing and crystallisation in determining petrologic indicators of volcanic processes.

24 VMSG 2013 – Oral Presentation Abstracts

Degassing regime of Hekla volcano Triple magma batches and a in 2012 complex eruption history of a

E. ILYINSKAYA*1,2, A. AIUPPA3,4, B. BERGSSON1, T. monogenetic volcano: Geochemical FRIDRIKSSON5, A.A. OLADOTTIR5, F. OSKARSSON5, K. 1 1 4 analysis of Mt. Rouse, Newer LECHNER , R. YEO , G. GIUDICE Volcanics Province, Australia 1 Icelandic Meteorological Office, Reykjavik, Iceland. (*[email protected]) J. BOYCE*1, I. NICHOLLS1, R. KEAYS1, P. HAYMAN1 2 British Geological Survey, Edinburgh, EH9 3 LA. 1 3 School of Geosciences, Monash University, Clayton, VIC University of Palermo, Palermo, Italy. 3800, Australia. (*[email protected]) 4 INGV, Palermo, Italy. 5 Iceland GeoSurvey, Reykjavik, Iceland. Mt. Rouse is the largest eruption centre in the Newer Volcanics Province (NVP), a continental intraplate basaltic Hekla is one of the most frequently active, yet also one volcanic field. With triple the magma volume of that of the most unpredictable volcanoes in Europe. It is erupted from other volcanic centres in the province, Mt. unknown whether the frequent activity of Hekla during the Rouse is a composite volcano of lava and pyroclastic past century is a beginning of a new eruptive trend. There is deposits, featuring at least eight eruption points and a lava also still a significant uncertainty about the depth of Hekla’s field extending at least 60 km to the coast. magma source, and the intrusion pathways. Monogenetic volcanoes are the most abundant volcano In the summer of 2012 we collected an original data set type on Earth and are usually thought to involve single in order to quantify Hekla’s gas emissions during a magma batches and simple evolutionary histories. However, quiescent interval. The data set includes 1) near-continuous recent research reveals that this may not be the case for MultiGAS measurements over a 2 months period, 2) every volcanic centre. Detailed stratigraphic and quantification of CO2 flux (emitted through diffuse geochemical analysis of Mt. Rouse reveals three distinct degassing) and 3) direct sampling of gases for magma batches and a complex eruption sequence.. There is compositional and stable isotope analysis. evidence of both sequential and simultanous eruption of the Our findings show that Hekla’s gas emissions are three magma batches, which differ in chemical composition, dominated by CO2, and restricted to the top crater which ranging from basanites to trachybasalts through to alkali erupted last in 1981. This is an interesting result as more basalts. The southern cone features a basal sequence of recently active craters (1991 and 2000) have higher ground batch C then B scoriae and batch A lava before becoming temperatures, but no detectable degassing. The carbon more complex. An unusual proximal surge deposit isotope signature in the gas is believed to be close to the that containing distinct products of two magma batches in the of the magma source. This presentation will discuss our form of Pele’s tears and hair from batch A and scoriae from results, and the obtained insights into Hekla’s degassing batch B is found between the basal lava and overlying behaviour. scoriae of batch B. Most surprisingly, this sequence shows evidence that the three magma batches erupted either from the same vent, or within close proximity to one another, with no evidence of mixing. Through preliminary petrogenetic modelling, it is suggested that the magma batches were sourced at different depths from an enriched mantle source. The fact that Mt. Rouse has undergone such a complex evolution, along with other recent research into supposedly monogenetic volcanic centres may have implications for petrogenetic modelling in the NVP and the study of other monogenetic fields.

25 VMSG 2013 – Oral Presentation Abstracts

Assembling a super-eruption: Shallow storage of dacites beneath Linking magma accumulation and Uturuncu volcano, SW Bolivia

eruption timescales at Toba D.D. MUIR1*, J.D BLUNDY1, A.C. RUST1 D.A. BUDD1*, V.R. TROLL1,5, E.M. JOLIS1, F.M. 1 School of Earth Sciences, University of Bristol, Wills DEEGAN1,3, V.C. SMITH2, M.J. WHITEHOUSE3, C. Memorial Building, Queens Road, Bristol, BS8 1RJ. HARRIS4, C. FREDA5, D.R. HILTON6, S.A. (*[email protected]) HALLDORSSON6 Volcanic unrest detected with InSAR recently drew 1 CEMPEG, Uppsala University, Sweden. attention to Uturuncu, a dormant dacitic stratovolcano in the (*[email protected]) Bolivian altiplano that last erupted 271 ka1. Magma 2 Research Lab. for Archaeology, University of Oxford, UK. intrusion in the mid to upper crust is thought to be 3 Swedish Museum of Natural History, Sweden. responsible for the ~80 km diameter deformation footprint 4 Dept. Geo. Sciences, University of Cape Town, South calculated as 1-2 cm/yr central uplift rate between 1992 and Africa. 20062. 5 Istituto Nazionale di Geofisica e Vulcanologia, Italy. Over a ~1 million year period dacite lavas and domes 6 Scripps Institution of Oceanography, UCSD, USA. have been erupted effusively at Uturuncu with no evidence of explosive activity. Mineral assemblages almost The Toba caldera located in Sumatra (Indonesia) is the exclusively consist of plagioclase, orthopyroxene, biotite, result of the four successive eruptions at 1.2, 0.84, 0.5 and ilmenite, magnetite and apatite set in a rhyolite glass. Rims 0.074 Ma [1]. This study presents oxygen isotope data for a and cores of plagioclase and orthopyroxene phenocrysts suite of whole rocks and quartz crystals erupted as part of span a large compositional range from An and Mg# , the Young Toba Tuff (YTT), an eruption event producing 45-90 30-70 respectively. Mean magmatic temperatures calculated from 2,800 km3 of material some 74 ka ago [1, 2]. Oxygen coexisting oxides from 18 samples are 854±50°C. H O isotope data have been obtained from whole rock 2 contents of 3.2±0.7 wt% have been measured in (conventional fluorination), single mineral grains (laser plagioclase-hosted melt inclusions using SIMS and CO is fluorination-LF) and in-situ (SIMS) in combination with 2 generally less than 100 ppm. Assuming magmas were cathodoluminescence (CL) imaging in order to establish the volatile-saturated, H O and CO compositions provide relative roles of magmatic fractionation, magma-crust 2 2 trapping pressures of 45 to 107 MPa with xH O from 0.9 to interaction and crystal recycling occurring in the Toba 2 1.0 in the fluid phase. magmatic system. The CL images of quartz crystals exhibit UTDM41B, a microlite-poor dacite with total defined patterns of zoning that often coincide with crystallinity of 37 vol%, a calculated magmatic temperature fluctuations in δ 18O values, allowing correlation of textural of 873±13°C and ƒO around NNO was chosen as a starting and compositional information. Measured δ 18O values 2 quartz composition for experimental study. Crystallisation phase from SIMS and LF range from 6.7 to 9.4 ‰, independent of equilibria experiments were run with the intention of their position on the crystal. Whole rock values, in turn, reaching equilibrium conditions from two end-member range from 8.2 to 9.9 ‰. The δ 18O values calculated magma synthetic starting compositions based on UTDM41B bulk- from quartz (assuming δ 18O = 0.7 ‰), suggest a quartz-magma rock and groundmass glass. Runs were conducted between minimum value of 6.0 ‰, similar to that expected from a 50 and 250 MPa, and 750 and 900°C under H O-saturated mantle derived magma [3], and a maximum value of 8.7 ‰. 2 and mixed volatile-saturated conditions in cold-seal Several quartz crystals, however, have rims with lower δ18O hydrothermal apparata and all requisite phases were values, suggesting a late, low-δ18O contaminant. This reproduced. At most P-T conditions, either orthopyroxene indicates multiple sources to the Toba system, including at or biotite are present. However, only at 870°C and pressures least two crustal components, one with high- and one with shallower than 100 MPa are both phases stable together. low-δ18O. Helium isotope data obtained from pyroxenes Crystallinities of experimental runs are consistently lower from the oldest Toba eruption (R/R = 0.7 and 1.8) are A than observed in natural rocks which contain a significant consistent with a significant crustal contribution. proportion of ante- and xenocrysts. Barometry calculations from feldspar and amphibole Calculated melt inclusion trapping pressures and suggest the magma chamber system resided at similar depth experimental findings indicate Uturuncu dacite magmas are (~ 10 km) for all four Toba eruptions. The system probably stored ≤3 km below surface – much too shallow to produce persisted as a crystal mush, which was repeatedly re- the broad deformation observed at the surface. If the mobilised by fresh magma injections. Crystal recycling, deformation has a magmatic source it is more likely consistent with compositional and textural features in most intrusion of magma into, or movement of magmas out of the of the YTT quartz crystals, seems an integral part of how Altiplano-Puna Magma Body at ~17 km below surface super-eruptions are assembled. Therefore, large volumes of without concurrent inflation of shallow reservoirs where isotopically heterogeneous sources were mixed to make the dacites are stored prior to eruption. final YTT cocktail, including a late low-δ18O contaminant, substantial high-δ18O crustal contributions, and considerable [1] Sparks et al. (2008) American Journal of Science 308, amounts of recycled antecrysts from the three previous 727—769. eruptive episodes of the Toba system. [2] Pritchard, M, E and Simons, M. (2002) Nature 418, [1] Rose & Chesner (1987) Geology 15, 913-917. 167—171. [2] Aldiss & Ghazali (1984) J Geol. Soc. 141, 487-500. [3] Taylor & Sheppard (1986) Rev. Min. 16, 227-271.

26 VMSG 2013 – Oral Presentation Abstracts

The behaviour of a volcanic system Petrological Cannibalism – the with two linked magma chambers chemical and textural consequences

S. BLAKE*1 of pulsatory growth of magma 1 Department of Environment, Earth & Ecosystems, The bodies Open University, Milton Keynes, MK7 6AA. J.D. BLUNDY*1, K.V. CASHMAN1 (*[email protected]) 1 School of Earth Sciences, University of Bristol, Bristol A typical volcanic plumbing system contains a deep BS8 1RJ, UK. (*[email protected]) magma storage reservoir which supplies magma to higher crustal levels and the surface. The parameters which control Few magma bodies are assembled in a single magmatic the rates of magma flow, chamber pressurization, and pulse. The growing consensus, based largely on field eruption in such a system are studied using a mathematical evidence and geochronology, is that assembly of magma model of two chambers linked by a conduit. The lower bodies large and small involved emplacement of multiple reservoir is hosted in (hot) viscoelastic rock and contains pulses into an expanding reservoir. Where successive pulses buoyant magma whereas the shallow chamber is hosted in differ significantly in composition there may be clear (cold) elastic low-density country rock. The model evidence of mingling and mixing of magmas with describes the time evolution of pressure in both chambers, contrasted physical properties, including synplutonic dykes the rates of magma flow into and, during eruption, out of and mafic enclaves. Where successive pulses have very the shallow chamber, and the volumes of magma similar composition, evidence for interaction between transferred. pulses may be cryptic, often limited to subtle textural During inflation of the shallow chamber, pressures and variations that can be mapped out in the field, but are not flow rates can respond on two timescales controlled by evident chemically. Pulsed emplacement leads, inevitably, either the elastic properties of the two chambers or the to fluctuations in temperature as successive pulses re-heat viscosity of the deep country rock. At short (elastic) their cooler, partially solidified ancestors. Depending on the timescales, the maximum achievable overpressure in the size of pulses and the time lapse between them the amount shallow chamber is determined by magma buoyancy in the of re-heating may vary from a few degrees to a few deep part of the system and the elastic properties and hundreds and may involve many cycles of heating and volumes of the two chambers. If this overpressure cannot cooling, although these become damped with time as the break open the chamber, then slow viscous relaxation of the body grows. These cycles of heating and cooling can deep reservoir’s surroundings drives more magma to the generate textures of crystal growth and resorption that shallow chamber, increasing the overpressure to a level now cannot be explained by any conventional process of magma limited solely by magma buoyancy. The time required to differentiation. These textures are especially well-preserved trigger an eruption is influenced by the elasticity of the in plagioclase because of slow diffusive re-equilibration of system, strength of the shallow country rock, buoyancy, and major (but not trace) components. Thermal modeling shows the ratio of the magma and country rock viscosities in the that the size and frequency of pulses is reflected in the deep part of the system. zoning styles of crystals, which may provide a powerful tool During deflation of the shallow chamber, eruption rate to retrieve such information. This approach is especially is moderated by decompression of shallow magma and useful when chemical zoning in major and trace elements influx of deep magma. For large country rock viscosities can be used to reconstruct the chemistry of the various and small deep reservoirs, the deep supply system behaves magma pulses to which an individual crystal was exposed elastically and eruption rate falls to zero over time. Lower and the timing of these pulses prior to eruption. We term the country rock viscosities around large deep reservoirs allow process of physical and chemical interaction between the deep reservoir to continuously leak magma, prolonging magma pulses and their partially consolidated ancestors the eruption. Although many basaltic systems appear to “petrological cannibalism” and propose that it can account operate in a solely elastic regime (e.g., Hawaii), the model for a wide range of textural and chemical features seen in suggests that large volume basaltic systems (flood basalts) magmatic rocks. We illustrate our proposal with field, and some viscous magmatic systems may operate in a textural and chemical examples from Mount St. Helens regime controlled by viscous deformation of deep country volcano, USA. rocks.

27 VMSG 2013 – Oral Presentation Abstracts

Plagioclase as recorder of magma- A new model for granitic crust interaction beneath the Faroe emplacement: The Newry Igneous Islands Complex, Northern Ireland

1 1 2 B. DAHREN*1, V.R. TROLL2, A. BARKER2, F.C. P. ANDERSON , C. STEVENSON , M. COOPER , R. 3 2 4 5 MEADE2 C.M. FREDA3 P.M. HOLM4 N. SØAGER4 ELLAM , I. MEIGHAN , C. HURLEY , J. REAVY , J. INMAN1, D. CONDON6, Q. CROWLEY7 1 CEMPEG, Department of Earth Sciences, Uppsala University. Villavägen 16, Uppsala 752 36, Sweden. 1 The University of Birmingham, UK. (*[email protected]) (*[email protected]) 2 Istituto Nazionale de Geofisica e Vulcanologia, Via di 2 GSNI, Belfast Vigna Murata 605, 00143 Rome, Italy. 3 SUERC, East Kilbride 3 Geological Institute, University of Copenhagen, Geocenter 4 Soil Mechanics, Lisburn, Northern Ireland Copenhagen, DK-1350, Copenhagen, Denmark. 5 University College Cork, Ireland 6 NIGL, BGS The opening of the North Atlantic in the early 7 Trinity College Dublin Paleogene resulted in extensive volcanism as evident in now extinct volcanic centres and large basalt piles in e.g. The Newry Igneous Complex (NIC) is comprised of Scotland, Ireland, Greenland and the Faroe Islands. This three largely granodioritic plutons, together with an volcanic region, commonly referred to as the North Atlantic intermediate-ultramafic body at its NE end. The recent Igneous Province (NAIP) is still highly active on e.g. Tellus survey of Northern Ireland (GSNI, 2007) has Iceland and Jan Mayen. The Faroe Islands Basalt Group highlighted several geophysical anomalies within the (FIBG) is itself linked to the early Icelandic hot spot (55 complex, including two previously unrecognised concentric Ma), and decompressional melting, resulting from rifting aeromagnetic structures. U-Pb zircon ages and a and the eventual breakup from east Greenland. geochemical study suggest that these features represent The FIBG is up to 6 km thick and is underlain by up to magmas intruded at different times, and that each pluton 40 km continental crust intruded by mafic sills, as suggested was emplaced through a series of inward-younging, by geophysical surveys. The exact nature of these concentric pulses. continental rocks is unknown, though previous studies have A combination of anisotropy of magnetic susceptibility presumed a Pre-Cambrian basement, probably overlain by (AMS) and field relations were used to investigate the sediments related to the pre-volcanic rifting. Potential emplacement of these pulses, with a view to linking this onshore equivalents of the basement rocks may be found in with one of the classic emplacement mechanism models NW Scotland and East Greenland. (i.e., cauldron subsidence, laccolithic inflation). AMS Here, we employ multiple geobarometric models reveals strong, dominantly oblate, concentric fabrics; whilst coupled with Sr, Pb and Nd isotope signatures in field mapping highlights an aereole of deformed host rock plagioclase crystals to decipher crustal influences in the surrounding the complex. Such features imply forceful Faroe basalts. Isotope analyses was performed In-situ emplacement and are characteristic of laccolithic inflation (microdrilling) as well as on whole rock and plagioclase (but not cauldron subsidence). However, analysis of field separates. The 87Sr/86Sr signatures range between 0.703 - relationships suggests that the complex was intruded as 0.705. Correlation of calculated magma storage depths with steep, concentric, sheet-like pulses, which preclude geochemical contamination signatures allows us to laccolithic inflation and are consistent instead with cauldron construct “virtual geochemical boreholes” through the subsidence. Therefore, the evidence fits neither of these basalts into the underlying crustal basement. classical emplacement mechanism models. The wide range of the isotopic signatures indicate a Further investigation of the host rocks has provided complex plumbing system with variable degrees and depth what seems to be an appropriate solution. The structure of levels of crustal contamination. Using the available data, we these suggest that the NIC was intruded into a tension- attempt to construct the general lithostratigraphy of the sub- releasing bend on a strike-slip fault. The local extensional basaltic basement from the combined geobarometry and regime resulting from this feature would have created the contamination patterns. tectonic conditions and some of the space for intrusion to take place. This occurred as steeply orientated sheets within a SW-migrating weakened zone. However, within sheets themselves magma pressure exceeded local lithostatic pressure, creating further space and causing the surrounding rocks to be deformed. Therefore, the NIC shows that granitic intrusions can show complex emplacement histories, with elements of more than one of the classical models.

Beamish, D., Kimbell, G. S., Stone, P. and Anderson, T. B., (2010). J. Geol. Soc. Vol 167, 4, p. 649-657. Geological Survey of Northern Ireland, 2007. The Tellus project: Proceedings of the end-of-project conference, Belfast,http://www.bgs.ac.uk/gsni/tellus/conference/ind ex.html.

28 VMSG 2013 – Oral Presentation Abstracts

Reconstructing the emplacement of Slurry remobilisation in a layered the Lago della Vacca complex, mafic sill (Franklin LIP, Victoria Adamello Batholith, Italy, through Island, Arctic Canada)

field observations, image analysis B. HAYES*1, J.H. BÉDARD2, C.J. LISSENBERG1 , C.D. and AMS BEARD3 1 School of Earth & Ocean Sciences, Cardiff University, A. SCHÖPA*1, C. ANNEN1, J. BLUNDY1, M. DE SAINT- Wales, UK. (*[email protected]) BLANQUAT2 AND P. LAUNEAU3 2 Geological Survey of Canada, Québec City, Canada. 1 School of Earth Sciences, University of Bristol, Wills 3 School of Earth Sciences, University of Bristol, Bristol, Memorial Building, BS8 1RJ Bristol, UK. UK. (*[email protected]) 2 Géosciences Environnement Toulouse / Observatoire Midi- The >2500 km Neoproterozoic (~723-716 Ma) Franklin Pyrénées, 31400 Toulouse, France large igneous province (LIP) is extremely well exposed and 3 Laboratoire de Planétologie et Géodynamique de Nantes, preserved within the NE-SW trending Minto Inlier on CNRS/Université de Nantes, 44322 Nantes, France Victoria Island. The magmatic plumbing system is dominated by sills (m’s-100 m’s in thickness), which To shed light into the emplacement style and sequence intruded into the sediments of the Shaler supergroup. These of the Eocene Lago della Vacca complex (LVC) in the sills were fed by localised feeder dyke systems, and there is southern Adamello Batholith, we used three different unequivocal evidence of syn-magmatic faulting, with the techniques to analyse fabrics in this granitoid intrusion. migration of melts and crystal slurries up-section along First, we measured magmatic silicate fabrics defined by faults1. Coeval ~1.1 km thick Natkusiak flood basalts the orientation of hornblende and biotite directly in the overlie the Shaler stratigraphy. Recent trace element and field. Second, we used an image analysis software [1] to isotopic work demonstrates the linkages between the sills obtain crystal distribution anisotropies in photographs of and lavas, as well as revealing internally heterogeneous rock surfaces taken in the field and of cut rock specimen. sills. Thus, we have been able to reconstruct the plumbing Third, we took samples for an anisotropy of magnetic system of a LIP. susceptibility (AMS) study to gain insight into the magnetic The sills have been divided into geochemical groups. fabrics of the LVC. Group A, the basal sills (below the Minto Inlet formation) In general, direct field measurements and image are LREE-enriched and are characterized by olivine- analysis results agree well with each other. Planar fabrics cumulate bases, with diabasic roofs. Sills higher up in the prevail indicative of forceful emplacement of the LVC as stratigraphy (Groups B and C) are typically unenriched and earlier injected magma pulses would have been deformed are characterized by porphyritic or sub-ophitic diabasic by later magma injections. Foliations commonly strike textures. The Lower Pyramid Sill (LPS), which we have parallel to the eastern and southern borders of the intrusion studied in detail here, is an example of one of the LREE- and dip steeply towards a common midpoint in the enriched sills. We believe, based on stratigraphic northwest. relationships, that this sill extends from its proposed feeder Although there are discrepancies between the site, the Uhuk massif some ~40 km to the east. The LPS is macroscopic silicate fabrics and the magnetic fabrics some its distal equivalent, and its gradual thinning from ~40 m at similarities are obvious. For instance, macroscopic and Uhuk to ~21 m at the LPS indicates a propagation direction magnetic foliations are deflected around the Blumone towards the west. Complex in line with an emplacement model of lateral The LPS shows remarkable layering for a thin magma movement and inflation [2]. This is supported by a magmatic body, being comprised of: (i) a lower chill; (ii) higher mean magnetic susceptibility in the vicinity of the lower border zone (LBZ; olivine gabbro); (iii) olivine- gabbroic Blumone Complex, reflecting changes to more cumulate (OZ); (iv) sub-ophitic diabasic roof (DZ); (v) mafic granite compositions. upper border zone (UBZ; diabase), capped by a chill. The As revealed by AMS and image analysis likewise, linear OZ is defined by a jump in olivine Fo and NiO contents fabrics dominate in the northwest of the LVC with moderate above the LBZ, as well as reversely zoned olivine. A thin plunges of lineations to the west. This could mimic magma layer of clinopyroxene-cumulates above the OZ possibly flow at higher levels of the intrusion not significantly formed from the interaction between evolved melts (sourced influenced by later injected magma pulses and agrees with from the olivine-slurry?), and the diabasic mush. Based on the concept that this part of the LVC is close to the source these relationships, we propose that an initial intrusion of region of the magma. primitive melt (average 12% MgO based on chilled margin To sum up, we combined different approaches to analyses) resulted in the formation of a diabasic mush. obtain fabrics in a silicic intrusion to link them to Replenishment led to the emplacement of an olivine-slurry emplacement modes and magma intrusion sequences. which underplated the crystallising diabasic mush, forming the OZ. Radiogenic isotopes (207/204Pb/206/204Pb) support this [1] Launeau et al. (2010) Two- and three-dimensional shape differentiation model, as they show that the LPS is fabric analysis by the intercept method in grey levels internally heterogeneous and that the OZ and DZ formed Tectonophysics 492, 230-239. from geochemically discrete magmas. [2] John and Blundy (1993) Emplacement-related deformation of granitoid magmas, southern Adamello [1] Bédard, J, H., et al (2012) GSA Bulletin, Vol 124, page Massif, Italy GSA Bull. 105, 1517-1541. 723-736.

29 VMSG 2013 – Oral Presentation Abstracts

Crystal-melt relationships and the Glacial loading probes mantle record of deep mixing and heterogeneity beneath Iceland

crystallisation in the AD 1783 Laki J. MACLENNAN*1, K.W.W. SIMS2, J. BLICHERT-TOFT3, eruption, Iceland E. MERVINE4, J. BLUZSTAJN4, K. GRÖNVOLD5 1 Earth Sciences, Cambridge (*[email protected]) D.A. NEAVE*1, E. PASSMORE2, J. MACLENNAN1, G. 2 Geology & Geophysics, University of Wyoming FITTON3, T. THORDARSON3 3 Laboratoire de Géologie de Lyon, ENS Lyon 1 Dept. Earth Sciences, University of Cambridge, 4 Department of Geology and Geophysics, Woods Hole Cambridge, CB2 3EQ, UK. (*[email protected]) 5 Institute of Earth Sciences, University of Iceland 2 Dept. Earth Science & Engineering, Imperial College, London, SW7 2AZ, UK. Glacial modulation of melting beneath Iceland provides 3 School of GeoSciences, University of Edinburgh, a unique opportunity to better understand both the nature Edinburgh, EH9 3JW, UK. and length scale of mantle heterogeneity. At the end of the last glacial period, ~13,000 yr BP, eruption rates were ~20- Recent studies in the north and southwest of Iceland 100 times greater than in glacial or late postglacial times have indicated that the composition of erupted basaltic and geophysical modeling indicates that rapid melting of the magmas is controlled by concurrent mixing and large ice sheet covering Iceland caused a transient increase crystallisation of variable mantle melts en route to the in decompression mantle melting rates. Here we present the surface. Careful thermobarometric calculations have first time-series of Sr-Nd-Hf-Pb isotopic data for a full constrained the depth of the crystallisation interval to glacial cycle from a spatially confined region of basaltic between the mid crust and uppermost mantle. In order to volcanism in Northern Iceland. Basalts and picrites erupted address the question of whether similar processes also take during the early postglacial burst in volcanic activity are place in the plumbing systems that feed the large fissure systematically offset to more depleted isotopic compositions eruptions characteristic of the Eastern Volcanic Zone (EVZ) than those erupted during glacial or recent (<7 kyr) times. we present the results of an investigation into crystal-melt These new isotopic data, coupled with major and trace relationships and deep magmatic processes in the large and element data, show that the mantle underneath northern environmentally damaging AD 1783 Laki eruption (Skaftár Iceland is heterogeneous on small (<100 km) scales. The Fires). The collapse of olivine-hosted melt inclusion trace temporal response of the isotopic compositions of the element variablity with progressive magmatic evolution basalts to glacial unloading indicates that the isotopic indicates that concurrent mixing and crystallisation has composition of mantle heterogeneities can be linked to their occurred in the deep plumbing system. Plagioclase melting behavior. The geochemical data can be accounted macrocrysts contain three distinct zones that also preserve a for by a melting model where a lithologically heterogeneous record of melt evolution and variability: high anorthite mantle source contains an enriched component which is cores, oscillatory zoned mantles and low anorthite rims. more fusible than the depleted component. Mineral-melt equilibrium partition coefficients indicate that While spatial variations in the compositions of basalts the rims are in equilibrium with the erupted carrier liquid. from mid-ocean ridges, seamounts and ocean islands have High-anorthite cores are more primitive than any other previously been understood in terms of such short- crystal or melt inclusion composition in the magma and lengthscale variations, prior studies have not been able to cannot be related to the carrier liquid by fractional deconvolve the effects of long wavelength variations in crystallisation models, which assume a single liquid line of melting process and bulk source composition. This unusual descent. High-anorthite cores may have grown from high sampling of mantle heterogeneity by glacial unloading Ca/Na melts of the shallow mantle with depleted provides strong evidence of the role of short- lengthscale compositions that have been mixed into the eventual carrier mantle lithological variation in controlling the composition liquid early in the course of magmatic evolution. of erupted basalts. This finding has important implications Furthermore the crystal size distribution (CSD) of for the compositional relationship between basalts and the plagioclase macrocrysts suggests plagioclase cores upwelling mantle: preferential sampling of enriched fusible represent an accumulated or assimilated population, acting streaks will bias the isotopic composition of the melt away as nucleii for the growth of oscillatory zoned plagioclase from the average of the rising mantle. The occurrence of mantles. Plagioclase mantle compositions may be related to such sampling bias may provide a mechanism for producing the carrier liquid by fractional crystallisation models long wavelength isotopic features in basalts from long- involving eutectic co-crystallisation with clinopyroxene and wavelength variations in the melting process and outflow olivine. Melt barometry indicates that the carrier liquid last rather than underlying long-wavelength mantle equilibrated with plagioclase, clinopyroxene and olivine in heterogeneity. the shallow crust at 1-2 kbar. However, clinopyroxene-melt barometry suggests that the bulk of macrocryst growth occurred in the mid crust at 2.5-6 kbar. Much of the macrocryst content of the magma occurs as glomerocrysts, of which only the rims in contact with the groundmass are in equilibrium with carrier liquid. Glomerocrysts therefore formed before rim growth, during the deposition of crystal mushes in the mid crust, which dissagregated on transport to the shallow crust prior to eruption.

30 VMSG 2013 – Oral Presentation Abstracts

Mission Immiscible for two Melting beneath the Izu volcanic subduction components; evidence arc: Constraints from uranium- from Pagan Volcano, Mariana arc series isotopes

*1 2 3 Y. TAMURA , O. ISHIZUKA , R.J. STERN , A. H. FREYMUTH*1, T. ELLIOTT1, Y. TAMURA2 NUNOKAWA1, H. SHUKUNO1, H. KAWABATA1, Y. 1 Bristol Isotope Group, University of Bristol, UK HIRAHARA 1, Q. CHANG1, T. MIYAZAKI1, J. KIMURA1, (*[email protected]) R.W. EMBLEY4, S. BLOOMER5, Y. TATSUMI1 2 Institute for Research on Earth Evolution, Japan Agency 1 IFREE, JAMSTEC, Yokosuka, Japan. for Marine-Earth Science and Technology, Yokosuka, (*[email protected]) Japan 2 GSJ/AIST, Tsukuba, Japan. 3 U. Texas at Dallas, Richardson, USA. Uranium-series isotopes can provide information about 4 NOAA, Newport, USA. the time-scales of processes in subduction zones such as 5 OSU, Corvallis, USA. fluid transfer from the subducted slab to the mantle wedge, melt generation within the mantle wedge and ascent of the Pagan is one of the largest (2,160 km3; Bloomer et al., melts to the surface. Yet, critical aspects of these isotopic 1989) volcanoes along the Mariana arc magmatic front, but systems are not well understood. Traditionally, 238U most of the volcano is submarine and unexplored. excesses over 230Th in arc magmas has been interpreted to Bathymetric mapping and ROV Hyper-Dolphin (HPD1147) reflect the relative affinity of U for an aqueous fluids that dive on the NE submarine flank of Pagan were carried out transports it into the subarc mantle while Th remains during NT10-12 (R/V Natsushima) in July 2010. There are immobile. Recent experimental work (e.g. Klimm et al., no systematic differences between subaerial and submarine 2008) suggest that U-Series disequilibria are primarily lavas with > 52 wt % SiO2, suggesting derivation from the controlled by properties of the accessory phases present in same magmatic system. Twenty least-fractionated basalts the subducting slab during dehydration rather than the fluid.

(48.5-50 wt % SiO2) extend to higher MgO (10-11 wt %) Moreover, recent U-Series models for the Mariana arc and Mg# (66-70) than subaerial lavas. Compositions of (Avanzinelli et al., 2012) infer that some Th is transferred to olivine (up to Fo94) and spinels (Cr# up to 0.8) suggest that the arc in the ‘fluid’. These considerations potentially affect Pagan primitive magmas formed from high degrees of conclusions on the time-scales of subduction zone mantle melting. processes. Another uncertainty is the origin of trace element Two geochemical groups of clinopyroxene olivine enriched end-members in arc magmas, some of which have basalts (COB1 and COB2) can be distinguished at similar Th excess over U. These have so far been interpreted as 10-11 wt % MgO; these erupted about the same time, 500 m dominated by sediment melts. apart. Lower TiO2, FeO, Na2O, K2O, incompatible trace Both of these aspects are addressed by our study of U- element abundances, and Nb/Yb suggest that COB1 formed Th disequilibria in samples from the Izu volcanic arc. A from higher degrees of mantle melting. In addition, LREE- comparison to other arcs worldwide and in particular to the enrichment and higher Th/Nb in COB2 contrast with LREE- more extensively studied Mariana arc in the southern part of depletion and lower Th/Nb in COB1. Higher Ba/Th and the Izu-Bonin-Mariana (IBM) arc system shows that the Izu Ba/Nb and lower Th/Nb indicate that main subduction arc is highly depleted in most incompatible elements which addition in COB1 was dominated by hydrous fluid, whereas allows components derived from the subducting slab to be that in COB2 was dominated by sediment melt. Sr-Nd-Pb- more clearly identified. Samples from several islands of the Hf isotopes are also consistent with this scenario. Izu arc have large 238U excesses over 230Th, showing that the Hydrous fluid could not be miscible with silicate compositions of magmas from this part of the IBM arc are (sediment) melt in the depth of the subducting slab below dominated by fluids derived from the subducting slab. the volcanic front (Kawamoto et al., 2012; Mibe et al., Sediments subducted at the Izu arc segment are 2011), which might have resulted in two neighboring, but fundamentally different to those of the Mariana arc and completely different primary magmas. In contrast to Pagan, should lead to lower (230Th/232Th) in the Izu samples. we observed two primary magmas (COB and POB) in the However, the opposite is observed, suggesting that not NW Rota-1 volcano (NWR1), ~40 km behind the volcanic sediments alone constitute the enriched end-member but front. NWR1 COB has a greater subduction component, that at least for some arc magmas an additional source is both hydrous fluid and sediment melt, than POB, perhaps needed. This could be upper parts of the oceanic crust that reflecting that the subducting slab below NWR1 is > 100 melt together with the sediments at subarc depths. km deeper than that beneath Pagan. At such higher pressures, hydrous fluid and sediment melt could mix into a Klimm, K., Blundy, J.D., Green, T.H.(2008) Journal of uniform supercritical fluid (Kawamoto et al., 2012; Mibe et Petrology 49, 523-553 al., 2011), with different proportions yield distinct NWR1 Avanzinelli, R., Prytulak, J., Skora, S., Heumann, A., COB and POB (Tamura et al., 2011). Koetsier, G., Elliott, T. (2012) Geochimica et Cosmochimica Acta 92, 308-328 Bloomer, S. H. et al. (1989) Bull Volc 51, 210-224. Kawamoto, T. et al. (2012) PNAS in press. Mibe, K. et al. (2011) PNAS 108, 8177-8182. Tamura, Y. et al. (2011) J Pet 52, 1143-1183.

31 VMSG 2013 – Oral Presentation Abstracts

Diatreme volcanism facilitating Pb- The Comsos Greenstone terrane; Zn mineralisation in the Irish insights into a mineralised Archean Orefield? arc from U-Pb dating, volcanic

H.A. ELLIOTT1*, T.M. GERNON1, S. ROBERTS1, P.B. stratigraphy and geochemistry 2 REDMOND *1 1 A. DE JOUX , T. THORDARSON 1 Ocean and Earth Science, National Oceanography Centre, 1 School of GeoSciences, University of Edinburgh, UK University of Southampton, Southampton SO14 3ZH (*[email protected]) (*[email protected]) 2 Teck Ireland Ltd., 5 Wentworth Place, Wicklow, Ireland The Archean Kalgoorlie Terrane, within the Yilgarn The Limerick Basin in southwest Ireland is an important Craton, contains several world-class nickel-sulphide ore element of the Pb-Zn Orefield within the Irish Midlands. bodies. The origin of these ultramafic-hosted nickel Until the recent discovery of a cluster of basaltic diatremes sulphide deposits remains contentious, particularly in the within the Stonepark area, the carbonate hosted Pb-Zn Agnew-Wiluna Greenstone belt where recent reviews have deposits were not thought to be related to Lower reiterated a dominantly intrusive origin for thick, nickel- Carboniferous volcanics within the area. Thus, the genetic sulphide hosting, ultramafic adcumulate bodies associated relationship between mineralisation and magmatism is with felsic volcanics (1). The Cosmos mine site lies on the poorly understood and highly controversial. The diatremes western edge of the Agnew-Wiluna Greenstone belt and this emplaced into the Lower Carboniferous carbonate previously unstudied mineralised volcanic succession stratigraphy, are attributed to increased heat flow and contrasts markedly in age, geochemistry, emplacement magmatism during extensional tectonic activity in the mechanisms and probable tectonic setting to that of the Tournasian. The preferred NE-SW trend of diatremes majority of the belt (1,2). suggests that they might have been fault controlled. In close The underlying succession to the Cosmos mineralised proximity to the diatremes a series of extra-crater basaltic ultramafic body consists of a complex succession of both lava flows and pyroclastics (Knockroe Formation) is fragmental and coherent extrusive lithologies, ranging from commonly interbedded with argillaceous and crinoidal basaltic-andesites through to rhyolites, plus later-formed limestones formed in a shallow marine environment (Lough felsic intrusions. The occurrence of thick sequences of Gur Formation) [1]. The Knockroe sequence was likely amygdaloidal intermediate lavas intercalated with extensive sourced from the diatreme eruptions, given the apparent sequences of dacite tuff, coupled with the absence of marine thickening toward the diatremes, and similarities in both sediments or hydrovolcanic products, indicates that the composition and texture between the deposits. The large- succession, including the mineralised komatiite lavas, were scale geological relationships, low vesicularity of juvenile formed in a sub-aerial environment. Chemical composition lapilli [2] and other deposit characteristics suggest that of the non-ultramafic lithologies is dominated by a calc- eruptions were largely phreatomagmatic, shedding alkaline signature, indicative of a volcanic arc setting. REE volcaniclastic material into a shallow marine setting. Base data shows that the compositional variability was not metal mineralisation occurs as replacement of Black Matrix achieved via fractional crystalisation alone, and that crustal Breccias (BMB), formed by the passage of hydrothermal assimilation and/or different sources must be invoked to fluids through the limestone country rock. The BMB explain the observed basaltic-andesite to rhyolite magma signature mineral phases are calcite, quartz and dolomite. suite. The occurrence of diatreme clasts within mineralised BMB Recent U-Pb dating, undertaken on several samples suggests that mineralisation post-dates or is from various levels within the established stratigraphy, has contemporaneous with magmatic activity. The presence of indicated that the emplacement of the Cosmos volcanic dolomite within the lowest part of the diatremes can be succession took place between ~2739Ma and ~2653Ma, explained by the passing of BMB hydrothermal fluids making it significantly older and longer-lived than other through the lower sections of the diatremes before entering dated volcanic successions within the Kalgoorlie Terrane. the adjacent country rock. Extrusive periodic volcanism spanned ~55Ma with three cycles of bimodal intermediate/felsic and ultramafic [1] Somerville, I.D., Strogen, P., and Jones, G. (1992). volcanism occuring between 2739Ma and 2685Ma. Periodic Geological Journal, 27, 201-222 intrusive activity lasted for a further ~32Ma until ~2653Ma. [2] Ross, P., and White, J. (2012), Journal of Volcanology The age, composition and geochemistry, particularly a and Geothermal Research, 245-246, 55-67 lack of TTD affinity, of the intermediate and felsic succession at Cosmos contrasts with the adjacent Agnew- Wiluna greenstone belt (1), indicating the Cosmos succession is a separate, older terrane with a distinct sub- aerial extrusive volcanic succession formed in a long-lived arc setting.

[1] Florentini, Beresford, Barley, Duuring, Bekker, Rosengren, Cas & Hronsky (2012) Economic Geology, 107, 781-796. [2] Rosengren, Cas, Beresford & Palich, (2008) Precambrian Research 161, 34-52.

32 VMSG 2013 – Oral Presentation Abstracts

Carbonatite genesis: An Rheology of three-phase magmas experimental approach in the M. PISTONE*1, L. CARICCHI2, P. ULMER1, E. REUSSER1, F. MARONE3, L. BURLINI1, CMASK-CO2 system 1 Department of Earth Sciences, ETH-Zurich, S. C. MCMAHON*1, M. J. WALTER1, D. K. BAILEY1 Clausiusstrasse 25, CH-8092, Zurich, Switzerland. 1 Department of Earth Sciences, University of Bristol, BS8 (*[email protected]) 1RJ. (*[email protected]) 2 Department of Mineralogy, University of Geneva, Rue des Maraîchers 13, CH-1205, Geneva, Switzerland. Liquid immiscibility between carbonate and silicate 3 Swiss Light Source, Paul Scherrer Institute, Villigen, melts is a possible mechanism for the genesis of Switzerland. carbonatites and associated silica-undersaturated rocks [1]. Compelling textural evidence for liquid immiscibility is We present experimental results from a study aiming to displayed by carbonate globules associated with silicate constrain the dependence of rheology of three-phase melts of melilititic compositions at numerous carbonatite magmas (ranging from dilute suspensions to crystal provinces [2]. These textures include sharp curved menisci mushes) on the viscosity of the suspending silicate melt, on against a silicate melt, budding and coalescing of globules, the relative contents of crystals and bubbles and on the and dumb-bell and amoeboid forms. One possibility is that interactions occurring between the three phases during unmixing occurs as magma evolves in the shallow mantle or deformation. Hydrous haplogranitic magmas containing crust [3]. variable amounts of quartz crystals (between 24 and 65

However, carbonate globules are sometimes found in vol.%), and a fixed bubble volume (9-12 vol.% CO2-rich deeply sourced mantle xenoliths and as inclusions in bubbles) were deformed in simple shear with a Paterson- xenocrystic olivines with primitive compositions [4]. One type rock deformation apparatus at high temperatures (823- such example of these features is at the Calatrava Volcanic 1023 K) and high pressure (200 MPa), in strain-rate Province in central Spain; an alkaline ultramafic province stepping (5·10-5 s-1 - 4·10-3 s-1) from low to high deformation comprising over 250 monogenetic cones and vents [5]. rate. The rheological results suggest that three-phase Here, the carbonate ‘globules’ are possible examples of suspensions are characterized by strain rate-dependent near-primary carbonatitic melts derived at high pressure in rheology (non-Newtonian behavior). Two kinds of non- the mantle. Newtonian behaviors were observed: shear thinning Experiments show that immiscibility can occur in (decrease of viscosity with increasing strain rate) and shear partial melts of carbonated eclogite at 3 GPa [6]. To thickening (increase of viscosity with increasing strain rate). investigate the possibility of a primary origin for Microstructural observations suggest that: shear thinning carbonatite-silicate melts at the carbonated peridotite dominantly occurs in crystal-rich magmas (55-65 vol.% solidus, we have conducted piston cylinder experiments in crystals) because of crystal size reduction and shear the synthetic system CaO-MgO-Al2O3-SiO2-K2O-CO2 localization; shear thickening prevails in dilute suspensions

(CMASK-CO2) at 30 kbar (equivalent to ~100km depth). (24-44 vol.% crystals) due to outgassing promoted by Potassium is a significant constituent at many alkaline bubble coalescence. We also propose possible scenarios of volcanic provinces associated with carbonatites, with high shear thickening and shear thinning rheology of magmas contents in unusual rock types such as kamafugites [7]. ascending within volcanic conduits. Given the widespread evidence for the presence of CO2 in the upper mantle [8], an anhydrous system has been investigated to assess the role of CO2 in carbonatite generation. We also test the hypothesis of whether H2O is necessary for immiscibility in the mantle. Our experiments will track isobaric invariant equilibria where liquid coexists with an assemblage of olivine, garnet, clinopyroxene, orthopyroxene and carbonate. These phase relations can be used to determine the solidus temperature for a variety of model mantle lherzolite compositions, and provide the composition of solidus and near-solidus melts in a carbonate-bearing mantle. Geochemical and textural observations of the experimental products, in comparison with natural rocks, will have wider implications for the genesis of carbonatites and their associated silicate rocks.

[1] Le Bas, (1987), Geol Soc, London, Special Publications 30. [2] Bailey & Kearns, (2012) Mineral Mag, 76(2), 271– 284. [3] Lee & Wyllie, (1998) J. Pet. 39(11-12), 2005-2013. [4] Humphreys et al., (2010) Geology 38(10), 911-914 [5] Bailey, K. et al. (2005). Mineral Mag 69, 907-915. [6] Dasgupta et al., (2006) J. Pet. 47, 647-671 [7] Bailey & Collier, (2000) Mineral Mag, 64(4), 675–682. [8] Dalton & Presnall, (1998a). Contrib Mineral Pet, 131(2), 123–135.

33 VMSG 2013 – Oral Presentation Abstracts

Disturbed 40Ar/39Ar ages in basalt Taking geology to the IMAX: 3D lavas: Chemical and X-ray and 4D insight into geological computed tomographic (CT) processes using micro-CT

evidence for fluid/basalt chemical K. J. DOBSON*1, P.D. LEE1, D.J. BROWN2, T. interaction TOMKINSON2, E.L. CRAMER3, S.C.SHERLOCK3, C. PUNCREOBUTR4, K.M. KAREH4 E.L. CRAMER*1, S.C. SHERLOCK1, K.J. DOBSON2, 1 Manchester X-ray Imaging Facility, School of Materials, A.M. HALTON1, S. BLAKE1, T.L. BARRY3, P.D. LEE2, University of Manchester, Oxford Rd., M13 9PL. S.P. KELLEY1, D.W. JOLLEY4. (*[email protected]) 1 Department of Environment, Earth and Ecosystems, The 2 School of Geographical & Earth Sciences, University of Open University. Milton Keynes. MK7 6AA. Glasgow, G12 8QQ. (*[email protected]) 3 Department of Environment, Earth and Ecosystems, The 2 Manchester X-Ray Imaging Facility (MXIF), School of Open University, Milton Keynes, MK7 6AA. Materials. University of Manchester, RCaH, Didcot, 4 Department of Earth Science and Engineering, Imperial OX11 0FA. College London, SW7 2AZ. 3 Department of Geology, University of Leicester, University Road, Leicester. LE1 7RH. Geology is inherently dynamic. Full understanding of 4 Geology and Petroleum Geology, School of Geosciences, the geological system can therefore only be achieved by University of Aberdeen, Aberdeen. AB24 3UE. considering the processes by which change occurs. Analytical limitations mean that our existing knowledge has Being able to accurately model fluid migration through been largely developed from ex situ analyses of the a basalt would be a fundamental step forward in our products of geological change, rather than of the processes understanding of post-emplacement effects upon the themselves. “Snap shot” sampling using 2D sections taken potential disturbances to K and Ar, and ultimately its effects through 4D systems has limited ability to capture 3D and on the 40Ar/39Ar dating system. Here we explore whether 4D behaviour. Serial sectioning and experiments quenched such effects can explain observed intralava 40Ar/39Ar age at different times can give some insight into the third and variations in a suite of lavas from the Faroe Islands. fourth dimension, but the true scaling of the processes from Vesicular Palaeogene basalts from the Malinstindur and generally 2D laboratory to the 4D crust is still poorly Enni Formations, Faroe Islands were sampled for 40Ar/39Ar understood. dating and textural analysis. Potential reservoirs and Micro computed tomography (uCT) can visualise the pathways for fluids through our selected basalts are internal structures and spatial associations within interconnected vesicles, most of which appear to be geological samples non-destructively, at pixel resolutions partially or fully filled with various species of precipitated from 200 microns down to 50 nanometres. As well as minerals. Using CT imaging, the size, shape and enabling detailed descriptive assessment in 3D, uCT data interconnectivity of the vesicles was measured. permits a range of quantitative analyses, and can provide the Early results suggest a high level of vesicle geometric data for FEM, CFD and other modelling connectivity, while initial electron microprobe chemical techniques. 3D assessment allows much better element maps indicate the presence of K within the vesicle understanding of the role of the complex geometries and fills. associations within the samples; but the challenge of These early results suggest that K-bearing fluids may capturing the processes that generate these structures have led to post-emplacement alteration and will be further remains. To this end we have developed the experimental examined for information on processes controlling the re- capability to perform in situ melt and deformation distribution of K and Ar in basaltic rocks. experiments using synchrotron based x-ray tomography to achieve a full 3D data set per second; taking quantification of the igneous system into 4D. We will present examples from recent work showcasing these capabilities, visualising features such as compositional zonation in feldspars, vesicle bubble structures in low grade ignimbrites, and rarely reported crystalline precipitations in basalt vesicles networks in 3D. We will show results from quantitative mineral mapping, characterisation of crystal and vesicle size distributions, and determination of preferred crystal orientations. Finally, we will present results from in situ high temperature melting and deformation experiments, where we have mapped changing melt and crystal locations, geometries and crystal motions during extrusion. We will discuss how these imaging and quantitative techniques can be applied to the volcanic and magmatic system, and how uCT can begin to record extrusion, flow, crystallisation and deformation in real time.

34 VMSG 2013 – Oral Presentation Abstracts

Ultra-deep drilling into arc crust Buoyancy of plume-sourced ash Y. TAMURA*1, Y. TATSUMI1, 2, O. ISHIZUKA1, 3, R.J. clouds: Implications for ash 4 5 6 7 STERN , J.B. GILL , J.A. PEARCE , R. ARCULUS AND transport modelling OTHERS R.S.J. SPARKS1, R. BAINES2, R. BURDEN1, S. 1 IFREE, JAMSTEC, Yokosuka, Japan. ENGWELL1, A. HOGG3, H.E. HUPPERT1, C. JOHNSON3, (*[email protected]) 1 1 2 J. KANDLBAUER , J.C. PHILLIPS AND M. Kobe University, Japan. 3 3 GSJ/AIST, Tsukuba, Japan. WOODHOUSE 4 U. Texas at Dallas, Richardson, USA. 1 School of Earth Sciences, University of Bristol, UK. 5 UCSC, USA. (*[email protected]) 6 Cardiff University, UK. 2 Dept. Infrastructure Engineering, University of Melbourne, 7 ANU, Australia. Australia. 3 School of Mathematics, University of Bristol, UK. What is raw and juvenile continental crust? Furthermore, how does it form and evolve into mature Volcanic plumes ascend high into the atmosphere where continental crust? The continental crust we observe on the they spread out at a level of neutral buoyancy to form surface of the earth has been deformed, metamorphosed, intrusions. The structure of these intrusions depends on the and otherwise processed perhaps several times from its relative strength of the intrusions, the ambient wind and the creation in subduction zones to the present. It’s impossible local atmospheric stratification. In a strong wind moderate to imagine a wild tuna fish from opening a can of processed to weak sized eruptions form bent over plumes. While tuna; the same might be said about juvenile versus mature typically in more powerful eruptions or in eruptions with a continental crust. Although there are many examples of weak wind, they form umbrella clouds, which spread in all accreted arc crust on the margins of continents, during- directions. Irrespective of the wind the plumes eventually reach dynamical equilibrium with the wind field further and/or post-collision geochemical changes are widespread, from the volcanic source. The motion of such plume-fed and we don’t have the ability to observe active crust- intrusions is governed by buoyancy. The spreading of forming processes in modern arcs except by what we can intrusions is controlled by the volumetric flux of the feeding infer from eruptions at the surface, and by remote sensing of plume at the height of neutral buoyancy and the density arc interiors. “ULTRA-DEEP DRILLING INTO ARC stratification in the atmosphere, but not by the density of CRUST” is the best way to sample unprocessed juvenile intrusion itself. For the case of a symmetrically spreading continental-type crust, to observe these active processes that umbrella cloud the thickness decreases linearly with produce the nuclei of new continental crust, and to examine distance. Although more complex in detail, intrusions the nature of juvenile continental crust as first generated at affected by the wind also thin quite rapidly with distance. intra-oceanic arcs. Buoyancy thinning can explain why ash clouds are observed Key questions for comprehending arc crust formation to become very thin quite close to source. Advection are: (1) What is the nature of the crust and mantle in the diffusion models are now widely used to forecast ash clouds region prior to the beginning of subduction? (2) How does dispersal and ash deposition. Such models typically assume subduction initiate and initial arc crust form? (3) What are ash is dispersed vertically above the source and assume ash the spatial changes of arc magma and crust composition of particles act as heavy (sedimenting) tracers that are spread the entire arc? (4) How do the middle arc crust evolve? by atmospheric diffusion. Buoyancy effects are ignored. We Possible strategies for answering these questions include contend that such models are not a correct description of the physics of ash clouds in regions where buoyancy effects are drilling by IODP at the IBM arc system. IODP has significant. For very powerful eruptions buoyancy effects proposals to drill at the IBM, including three non-riser holes are dominant to distances of hundreds of kilometres or (IBM-1, IBM-2 and IBM-3) and one riser, ultra-deep hole more; it seems unlikely that an advection diffusion model (IBM-4), which answer these questions, respectively, and could reproduce observed ash distributions since such the four drillings result in comprehensive understanding of models cannot have upwind or very extensive cross-wind the arc evolution and continental crust formation. JR spreading. For weaker plumes that are markedly affected by drillings at three sites (IBM-1, IBM-2 and IBM-3) are wind, advection-diffusion models are useful mathematical scheduled in 2014. descriptions that can be calibrated to give good forecasts of We had a workshop in Hawaii from September 18 to ash transport. However, this does not mean they are good September 21, 2012, which aimed to gather a wide range of physical models of the process. Models of buoyancy geophysicists, geologists, geochemists and petrologists who spreading suggest that it can be the main cause of lateral are interested in the nature of arc crust and how this is spreading of wind blown clouds to significant distances modified in collision zones and preserved in continental (perhaps tens or hundreds of kilometres). Operational crust (http://www.jamstec.go.jp/ud2012/). Our goal has models of ash dispersal are likely to remain structured as been to discuss the merits, methods and implications of advection diffusion models, so they may need some “ULTRA-DEEP DRILLING INTO ARC CRUST” from empirical adjustments to take account of buoyancy. For both thematic (formation of continental crust) and regional example it might be better to have source terms, which assume ash is concentrated in narrow height intervals above (Izu-Bonin-Mariana) scope. the source (at one level rather than distributed vertically). I’d like to show the IODP ‘Project IBM’ and discussion However, it seems unwise to continue using such models in the Hawaii workshop. The IODP proposals and abstracts for very powerful eruptions. of attendees are uploaded in the website (http://www.jamstec.go.jp/ud2012/) and the workshop report will also appear on the web until the end of 2012.

35 VMSG 2013 – Oral Presentation Abstracts

The duration of volcanic eruptions: Climate and carbon cycle response Controls and forecasts to the 1815 Tambora eruption: Pre-

L.S. GUNN *1, S. BLAKE 1, C. JONES2, H. RYMER1 industrial versus future Earth 1 Environment, Earth and Ecosystems, The Open University, system simulations Milton Keynes, MK7 6AA. (*[email protected]) J.KANDLBAUER*1, P.O. HOPCROFT2, R.S.J. SPARKS1, 2 Mathematics, Computing and Technology, The Open P.J. VALDES2 University, Milton Keynes, MK7 6AA. 1 Department of Earth Sciences, University of Bristol, Wills During volcanic eruptions a pressing question is “How Memorial Building, Queen’s Road, BS8 1RJ, Bristol, long will the eruption last?” A period of continuous magma UK. (*[email protected]) discharge during basaltic eruptions can range from less than 2 School of Geographical Sciences, University of Bristol, one day to several years. Such a range of possible durations University Road, BS8 1SS. Bristol, UK. can lead to considerably different consequences that require different responses. A greater understanding of the The sulphur released by the 1815 Tambora eruption controlling factors on eruption durations, and the and converted to H2SO4 aerosols in the stratosphere resulted development of a tool to help constrain probable eruptions in a maximum global cooling of about 1°C in summer 1816. durations would be a great benefit to emergency response The cold climate was responsible for crop failures, leading planning and provide insight on sub-volcanic processes. to serious famine and high food prices in Europe and We present historical datasets of basaltic volcanic Northern America. 1816 became widely known as the ‘year eruptions from Iceland, Mt Etna (Sicily) and Piton de la without summer’. Fournaise (Indian Ocean) and assess variations in eruption We performed a series of climate simulations with the durations at and between different volcanoes. Statistical UK Met Office model HadGEM2-ES to assess if a Tambora analysis of the data indicates a likely volcano specific eruption in a futuristic high CO2 climate in 2045 (RCP 6.0 control on eruption duration. For example on Iceland, 56 % radiative forcing scheme) would lead to a different outcome of basaltic eruptions from volcanic systems situated within than in a ‘1815-like’ pre-industrial environment. the active rift zone have durations of less than or equal to 10 First results show that in both scenarios the temperature days, whereas 92 % of those outside of this zone last longer decreases by about 1°C the year after the eruption and than 10 days. global precipitation reduces by about 4% in summer 1816. A probabilistic statistical model has been developed to Interestingly, the vegetation productivity, as well as the forecast the duration of future volcanic eruptions at the different plant fractions do not show any strong relative studied volcanoes. The model also forecasts the eventual anomalies between the two scenarios, although the duration of an eruption which has already been on-going for vegetation distribution provides a fairly different initial a known amount of time and the potential use of the model model situation. in a real life situation is demonstrated.

36 VMSG 2013 – Oral Presentation Abstracts

Newly discovered components of The nature and scale of lava-water- magmatism from Satorini are sediment interaction: An example revealed during cryptotephra from the Fife-Midlothian Basin, studies of marine cores Kinghorn, eastern Scotland 1 2 3 4 C. SATOW , E. TOMLINSON , P. ALBERT , S. COLLINS , H. RAWCLIFFE*1, D. BROWN1, B. BELL1 5 6 7 5 K. GRANT , S. WULF , L. OTTOLINI , E. ROHLING , M. 1 3 1 8 3 School of Geographical and Earth Sciences, University of MENZIES , S. BLOCKLEY , V. SMITH , C. MANNING , 1 Glasgow, Gregory Building, Lilybank Gardens, J. LOWE Glasgow, G12 8QQ, UK.

1 (*[email protected]) Dept. of Geography, RHUL, UK. (*[email protected]) The Carboniferous-Permian Igneous Province of 2 Dept. Geology, Trinity College Dublin, Dublin, Ireland northern Britain records the complex interplay of competing 3 Dept. of Earth Sciences, RHUL, UK volcanic and sedimentary systems during rifting. The Early 4 Dept. Earth Sciences, University of Durham, Durham, UK Carboniferous Fife-Midlothian Basin at Kinghorn, in Fife, 5 University of Southampton, National Oceanography eastern Scotland, comprises a 485m thick succession of Centre, Southampton, UK. basaltic lavas, interbedded with a variety of siliciclastic and 6 Helmholz Centre Potsdam, GFZ German Research Centre carbonate sedimentary rocks, and volcaniclastic rocks. A for Geosciences, D-14473, Potsdam, Germany. range of depositional environments from sub-aerial through 7 Institute of Geosciences and Earth Resources, University fluvio-deltaic to shallow marine/lagoonal have been of Pavia, Italy. recognised. The sequence broadly records a marine 8 RLAHA, University of Oxford, UK transgression; however, various uplift and subsidence

events and fluctuating accommodation space have Marine core tephra deposits have traditionally been used controlled the intrabasinal drainage system. In this study, as isochrons to link together environmental records, we characterise the processes of lava-water-sediment particularly in the Mediterranean region (e.g. Bourne et al interaction at both the basin and interface scale. 2010, Albert et al. 2012). Recent advances in detection and The lavas were typically emplaced in sub-aerial extraction techniques have augmented both the number of environments, but the presence of hyaloclastite, locally with known tephra layers, and the useful geochemical data which pillow fragments, and peperite, indicates eruption into can be extracted from them. Now the tephra layers can standing bodies of water and/or interaction with contribute invaluably to the construction of volcanic unconsolidated wet sediment. The presence of histories. phreatomagmatic lapilli-tuffs and ash aggregates also Visible and crypto-tephra layers were extracted from records interaction of magma with water. Background core LC21 in the Aegean Sea and geochemically analysed sedimentation is dominated by siliciclastic input to fluvial by EPMA (major elements) and LA-ICP-MS or SIMS (trace and marginal marine environments, but locally, the basin is elements). Highly precise dating information is derived inundated by pulses of reworked volcanic material. from the correlation of the core’s isotope stratigraphy to that At the interface between volcanic and sedimentary of the Soreq Cave speleothem in Israel (Grant et al. 2012). units, three distinct types of lava-water-sediment interaction The resulting volcanic chronology comprises 14 or 15 have been identified: i) loading/soft-sediment interaction (± eruptions; from Santorini (9 eruptions), Kos/Yali/Nisyros (2 pillows/hyaloclastite); ii) “passive” interaction and eruptions), Campanian (2 or 3 eruptions) and Pantellerian (1 formation of peperitic margins (± pillows/hyaloclastite), and eruption) volcanic systems, dating from ~166.1ka to the iii) “aggressive” interaction and formation of “invasive” present day. disaggregated peperite. We record the nature and scale of This work demonstrates that: these interactions and their local digenetic effects. • Tephra layers in distal settings preserve evidence of The accurate characterisation of these domains will aid eruptions from Santorini that were not previously our understanding of the processes that occur during lava- known from proximal deposits. water-sediment interaction. These data are of particular • Some of the Santorini magma compositions importance for facies analysis and reservoir characterisation identified in LC21 are not known from proximal in volcanic rifted margins that are subject to hydrocarbon deposits, but are comparable to the compositions of exploration. magmas that were present in the upper crust prior to

the Minoan eruption (Druitt et al. 2012). Tephra deposits in this marine core can date the • eruptions with very high precision through a novel dating technique (Grant et al. 2012).

Relative ages of eruptions from different volcanic • sources can be established using tephrostratigraphy.

Albert.P.G. et al. (2012) JVGR 229-230 pp 74-94

Bourne.A. (2010) QSR 29 pp 3079-3094 Druitt.T. (2012) Nature 482 pp 77-82 Grant et al. (2012) Nature in press

37 VMSG 2013 – Oral Presentation Abstracts

Inclined Vulcanian explosions at Assigning a volcano alert level: Soufriere Hills Volcano: Causes and Negotiating uncertainty, risk, and consequences complexity in decision-making

P. COLE*1,2, 3, A. STINTON2,3, R. STEWART2,3, H. processes 2,4 ODBERT 1 C.J. FEARNLEY 1 Earth Sciences, Plymouth University, UK 1 (*[email protected]) Institute of Geography and Earth Sciences, Aberystwyth 2 Montserrat Volcano Observatory, Montserrat, West Indies University, Llandinum Building, Penglais Campus, 3 Seismic Research Centre, University of the West Indies, Aberystwyth, SY23 3DB, UK (*[email protected]) 4 School of Earth Sciences, University of Bristol, UK A volcano alert level system (VALS) is used to More than 100 Vulcanian explosions have taken place communicate warning information from scientists to civil at Soufriere Hills Volcano between 1996 and 2010 and authorities managing volcanic hazards. This paper provides many of these have been well-observed and documented, the first evaluation of how the decision-making process with video, thermal video and photography. behind the assignation of an alert level, using forecasts of Such a rich observational dataset, together with volcanic behaviour, operates in practice. Using geophysical monitoring data and samples of the products ethnographic studies and interviews conducted from 2007- allows detailed analysis of these explosions, including their 2009 at five USGS managed volcano observatories (Alaska, initial moments. While many of the Vulcanian explosions Cascades, Hawaii, Long Valley, and Yellowstone) two key were relatively vertically directed events, with a quite findings are presented here. First, that observatory scientists symmetrical radial distribution of products such as ballistics encounter difficulties in interpreting scientific data and and pyroclastic density currents (PDCs), several others were making decisions about what a volcano is doing when associated with initially inclined eruption columns and at dealing with complex volcanic processes and high levels of least some laterally directed components. scientific uncertainty. Second, the decision to move Clear examples of non-vertical explosions occurred in between alert levels is based upon more than volcanic 1996, 2008 and 2010. Documentation of the products of activity and scientific information, with a complex some of these non-vertical events shows that they varied negotiation of social and environmental risks playing a considerably in lithology. However they all have irregularly crucial role. This research establishes that warning systems dispersed ballistic fields and /or PDCs of a range of types. are complex and non-linear, making decision-making Some explosions have occurred associated with an processes problematic in the face of intrinsic uncertainties unloading event, such as dome collapse, where a significant and risks. A consideration of different social science portion of the lava dome was removed over several hours approaches to risk would, therefore, be beneficial in resulting in an asymmetric explosion crater morphology volcanic hazard management insofar as these suggest (e.g. 17 Sept 1996 and 11 February 2010). effective practices for communicating scientific uncertainty In all cases crater asymmetry is a critical factor in and risk. contributing to the non-vertical nature of the explosion. Preferentially directed hazardous PDCs and /or ballistics are important consequences of these inclined explosions.

38 VMSG 2013 – Oral Presentation Abstracts

Pyroclastic granulation in explosive Continental crust formation in the volcanic eruptions Southern Central Andes: New

T.M. GERNON*1, M. WOOD1, R.J. BROWN2, C. insights from O and Hf isotopes in MEDLIN3, M.A. TAIT4 , T.K. HINCKS5 zircon 1 Ocean & Earth Science, University of Southampton, SO14 R. JONES*1, L. KIRSTEIN1, S. KASEMANN2, B. DHUIME3, 3ZH. (*[email protected]) T. ELLIOTT3, V. LITVAK4 2 Dept of Earth Sciences, Durham University, DH1 3LE 3 School of Geosciences, Monash University, Australia 3800 1 School of GeoSciences, University of Edinburgh, UK 4 Rio Tinto Limited, Perth, Western Australia 6000. (*[email protected]) 5 School of Earth Sciences, University of Bristol, BS8 1RJ. 2 Department of Geosciences, University of Bremen, Germany Potassic and ultrapotassic volcanism (e.g. kimberlites, 3 Department of Earth Sciences, University of Bristol, UK lamproites) typically involves the formation of diverging 4 Departamento de Ciencias Geológicas, Universidad de pipes or diatremes, which are the locus of high-intensity Buenos Aires, Argentina explosive eruptions. A conspicuous and previously enigmatic feature of diatreme fills are ‘pelletal lapilli’ — Subduction zones, such as the Andean convergent well-rounded clasts that consist of an inner ‘seed’ particle margin, are the main producers of new continental crust via with a complex rim, thought to represent quenched juvenile arc magmatism. Arc magmas and hence new continental melt (Gernon et al., 2012). Such clasts are widely crust are composed of variable contributions from mantle, documented in a range of pyroclastic successions on Earth. crustal and subducted reservoirs. This study aims to New observations of pelletal lapilli in kimberlites show they investigate how contamination of arc magmas in the coincide with a transition from magmatic to pyroclastic southern Central Andes has varied during the Cenozoic. behaviour, thus offering fundamental insights into eruption The study area lies within the currently volcanically dynamics and constraints on vent conditions. We provide inactive Pampean flat slab segment (~27º-33ºS) of the strong evidence that pelletal lapilli form by fluidized spray Central Andes. During the Miocene the angle of the granulation — a coating process used widely in industrial subducting Nazca plate shallowed, leading to the eastward applications. We propose that pelletal lapilli are formed migration of the magmatic arc and eventual termination of when fluid volatile-rich melts intrude into earlier arc magmatism in the Late Miocene [1]. Subduction volcaniclastic infill close to the diatreme root zone. erosion, tectonic erosion, and crustal contamination have all Intensive degassing produces a gas jet in which locally- been highlighed as important processes in the region [2,3,4]. scavenged particles are simultaneously fluidized and coated High resolution, in-situ oxygen and hafnium isotope by a spray of low-viscosity melt. Most fine particles are analysis and U/Pb dating has been carried out on magmatic either agglomerated to pelletal coatings or elutriated by zircon obtained from Late Cretaceous to Late Miocene powerful gas flows. The origin of pelletal lapilli is plutonics and volcanics collected from an east-west transect important for understanding how magmatic pyroclasts are across the Andean Cordillera. The information obtained transported to the surface during explosive eruptions. A from this mineral scale investigation has also been similar origin may apply to pelletal lapilli in a range of combined with thermobarometry and whole rock alkaline volcanic rocks including carbonatites, kamafugites major/trace element geochemistry. 18 and melilitites. Mantle-like δ O(zircon) and εHf(zircon) values suggest the Late Cretaceous to Mid Eocene arc magmatics were derived from mantle melts with little contribution from upper crustal material, either from the subduction of continental crust or from crustal assimilation. Oxygen and hafnium isotope values obtained for Oligocene to Miocene magmatics, combined with the presence of inherited zircon populations, reflects the assimilation of different basement terranes as arc magmatism migrated to the east. This demonstrates varying contamination of arc magmas with continental crust during the Cenozoic in relation to changing subduction zone geodynamics.

[1] Pilger, R, H., (1984), Journal of the Geological Society London, 141, 793 - 802. [2] Stern, C, R., (1991), Geology, 19, 78 - 81. Schematic showing the formation of pelletal lapilli in [3] Hildreth, W., and Moorbath, S., (1988), Contributions to kimberlite diatremes (Venetia and Letseng, southern Mineralogy and Petrology, 98, 455 - 489. Africa). [4] Stern, C, R., (2004), Rev. geol. Chile, 31, 161-206.

Gernon, T.M., Brown, R.J., Tait, M.A., Hincks, T.K. (2012) Nature Communications 3, 832.

39 VMSG 2013 – Oral Presentation Abstracts

Melting rocks with magma: MORB-like halogens in basalts of Sediment pyrometamorphism as a the Azores archipelago

tracer of magma flow locallisation L.D. JEPSON*1, R. BURGESS1, V.A. FERNANDES2, C. in sills and dykes BALLENTINE1 1 School of Earth, Atmospheric and Environmental C. GROVE*1, D.A. JERRAM2, R.J. BROWN1, J. GLUYAS1 Sciences, University of Manchester, Oxford Road, 1 Durham University, Department of Earth Sciences, South Manchester, UK. M13 9PL. Road, Durham. (*[email protected]) (*[email protected]) 2 DougalEarth Ltd. (www.dougalearth.com). 2 Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Invalidenstraße 43, 10115 Petrographic, mineralogical and geochemical data have Berlin, Germany. been used to characterise sill and dyke contacts with aeolian sandstones(the Twyfelfontein Formation, Namibia, 132 Ma The halogens (Cl, Br, I) are moderately volatile (Jerram et al., 1999)). These show a range of contact elements that exhibit incompatible behaviour during diagenesis and in extreme cases pyro-metamorphic melting, and are hydrophyllic; iodine is strongly reactions (pyrometamorphism – contact metamorphism fractionated by biological processes. Although the halogens where temperatures are hot enough to induce melting and share similar geochemical properties to the noble gases in pyrogenic mineral growth (Grapes, 2010)) Contact effects many systems, the heavy halogens in particular have been vary from minor compaction and carbonate cementation, underutilized as tracers, because of the analytical difficulties inerpreted to be caused by hot fliuds either from and-or related to determining their low abundances in geological circulated by the intrusion, adjecent to most contacts, to materials. partial melt of arkosic sediment components at sill-dyke A suite of 85 ocean island basalts was collected during junctions or multiple dyke intersections, where heat has fieldwork to the Azores, Portugal in 2011. Halogen been intesified to the point where pyrometamorhism compositions have been determined in a sub-set (12) of occurs. these basalts, from the islands of: São Miguel, Terceira, The most intense effects are where magma flow has Graciosa and Pico. Olivine and pyroxene separates were been locallised, such as at a sill-dyke junction. Here, the analysed using an extension of the Ar-Ar method – a feldspar component has melted and segregated from the neutron-activation technique that allows the halogens to be quartz component of the sandstone. Near to the heat source determined from noble gas isotopes formed during (slower cooling) the melt has crystallised into a potassium irradiation. The halogens are assumed to be mainly sited in feldspar, pyroxene and tridymite (quartz paramorph) matrix. melt inclusions observed within the mineral phases; noble Further away the melt matrix shows less seggregation and gases were liberated by a combination of crushing and has vitrified into a clear glass containing floating detrital stepped heating. Only bulk halogen ratios are quoted here. quartz rimmed with tridymite paramorphs (like hedgehogs). Initial results show that the Azores basalts have a Further above is a carbonate pore filling cement and both similar range in I/Cl (9.92-253x10-6) as previously reported feldspar and quarts granins are present, representing the for MORB, with the Br/Cl values offset to slightly higher boiling hydrothermal system. values (0.62-4.22x10-3). There appears to be some variation At dyke convergences, where >3 dykes come together between islands, observed in the I/Cl values: the basalts effects are also intensified. Melt and segregation is similar from São Miguel < Terciera and Pico < Graciosa. This to the above example, but a fluid-fluid like contact exists variation is consistent with a SE-NW oriented decrease in with the igneous dolerite. A boundary zone is developed in age along ~250km of the Terciera Rift. the dolerite that is enriched with quartz and arkosic melt transferred from the sediments. We infer magma flow locallisation within the magmatic plumbing system from pyrometamorphic intensity. In the case of the converging dykes, a feeder to a vent may have existed above.

Grapes, R. (2010) Pyrometamorphism. Springer. Jerram, D., Mountney, N., Holzförster, F. and Stollhofen, H. (1999) Internal stratigraphic relationships in the Etendeka Group in the Huab Basin, NW Namibia: understanding the onset of flood volcanism. Journal of Geodynamics, 28, 393-418.

40 VMSG 2013 – Oral Presentation Abstracts

Entablature Dihedral angles as a proxy for A.E.S. FORBES*1, S. BLAKE1, D.W. MCGARVIE1, H. crystallisation times in dolerites 2 TUFFEN . *1 2 M. HOLNESS , C. RICHARDSON 1 Department of Environment, Earth and Ecosystems, The 1 Dept. Earth Sciences, University of Cambridge, Downing Open University, Walton Hall, Milton Keynes, MK7 Street, Cambridge CB2 3EQ. (*[email protected]) 6AA (*[email protected]) 2 BP Institute, University of Cambridge, Cambridge. 2 Lancaster Environment Centre, Lancaster University,

Lancaster, LA1 4YQ The median of the population of augite-plagioclase-

plagioclase dihedral angles in mafic rocks (Θ ) varies Entablature is the term used to describe zones or tiers of cpp systematically within dolerite intrusions. Formation of irregular jointing in basaltic lava flows. It has previously augite-plag-plag three-grain junctions involves the growth been linked to lava-water interactions and forms when water of augite into the melt-filled space created by the from rivers dammed by the lava inundates the lava flow juxtaposition of two plagioclase grains. Partially crystallised surface, and in lava-water interactions in subglacial settings. samples from the Kiluaea Iki lava lake shows that three- There has been no previous in-depth study of the different grain junctions form first where the two plagioclase grains types of fractures present in entablature tiers and this is the meet at a high angle, while narrower melt pockets tend to focus of this work. cool through the glass transition before the melt crystallizes. A number of different fracture types have been Θ in the lava lake crust and in other rapidly cooled recognised in entablature outcrops of the Þjórsádalur valley, cpp dolerites is ~78˚, higher than the 60˚ expected if augite southwest Iceland. These are striae bearing column perfectly pseudomorphed the melt geometry. In more bounding fractures and pseudopillow fracture systems slowly cooled bodies, augite-plag-plag junctions are not which themselves consist of two different fracture types: formed by the intersection of two planar augite-plag master fractures with dimpled surface textures and boundaries, but are curved towards higher angles: Θ > subsidiary fractures with curved striae. The interaction of cpp 78˚. In the most slowly cooled dolerites, Θ may approach pseudopillow fracture systems and columnar jointing causes cpp the equilibrium value of 109˚. chevron fracture patterns commonly observed in The change in junction geometry (and hence Θ ) with entablature. An entablature tier is generally bound by both cpp decreased cooling rate is a consequence of a change in the an upper and lower colonnade of straight, regular, vertical relative growth rate of plagioclase and augite during the last columns. stages of solidification at the three-grain junction. Closely spaced striae and dendritic crystal textures in We measured Θ from 10-15 samples across each of a the entablature tier indicate rapid cooling. Master fractures cpp family of dolerite sills ranging in thickness from 40m to show a thin band with an evolved composition at the 300m. Θ varies smoothly and symmetrically across each fracture surface, and mineral textures show evidence of cpp sill. The smaller bodies have Θ ~78˚ at the margins, quenching of this material. We interpret this as late stage cpp rising to higher values in the centre. The widest bodies residual melt that is drawn into an area of low pressure show the same pattern of dihedral angle variation but also immediately preceding or during master fracture formation, have high values within a few tens of metres of their which is then quenched by an influx of water and/or steam margins. There is no straightforward control of sill when the master fracture fully opens. Master fractures thickness on average plagioclase grain-size, but the coarsest appear to be the main conduit for coolant entering the lava horizons are stratigraphically above the sill centre in every flow during entablature formation. case. We constructed simple conductive cooling models,

taking into account the latent heat of crystallisation. Θ cpp is a sensitive function of crystallisation time if that time exceeds >10 years. The high marginal angles in thickest sills are caused by localized sub-solidus modification of the grain boundary orientations, enhanced by the relatively fine grain-size of the chilled margins. Because grain-size information is dependent on (poorly known) crystal growth

rates for constraining cooling times, Θ cpp is a more reliable proxy for dolerite cooling rates. The new speedometer is applied to mafic rocks for which the cooling rate is unknown. In the eucritic meteorite

Juvinas, Θ cpp = 93 ± 3˚, suggestive of a crystallisation time of order 100 years and a minimum crustal thickness ~70m for the supposed source of Juvinas, the asteroid 4 Vesta.

Θcpp can also be used to determine relative intrusion age of Tertiary dykes in the Skaergaard Intrusion (E. Greenland).

41 VMSG 2013 – Oral Presentation Abstracts

The onset and evolution of pit crater Structures of the rift zone in collapse: Insights from events at northern Iceland

Pu'u O'o, Hawaii, in 2011 S. HUGHES*1, H. RYMER1 E.P. HOLOHAN*1,2, T.R. WALTER1, M.P.J. SCHÖPFER2,3, 1 Ecosystems, & Earth Sciences, The Open University, J.J. WALSH2, T. ORR4, M. POLAND4 Walton Hall, Milton Keynes, Bucks, MK7 6AA. (*[email protected]) 1 GFZ Potsdam, Sektion 2.1, Helmholtzstrasse 7, Potsdam

14467, Germany. (*[email protected]) There is speculation, based on historical ‘twinned’ 2 Fault Analysis Group, UCD School of Geological eruptions and interconnected faults and eruptive fissures Sciences, University College Dublin, Dublin 4, Ireland. that activity at Eyjafjallajökull and neighbouring Katla are 3 Department for Geodynamics and Sedimentology, linked (Dahm and Brandsdottir, 2007) and there are other University of Vienna, Althanstrasse 14, A-1090 Vienna, suggested ‘paired’ volcanoes further north (Gudmundsson Austria. and Hognadottir,́ 2007). Pressure changes at one of the 4 U.S. Geological Survey, Hawaiian Volcano Observatory, paired volcanoes may trigger activity at the other (Andrew Hawaii National Park, Hawaii, U.S.A. and Gudmundsson, 2008; Einarsson, 2008), although

geochemical evidence suggests the magma systems are not Deformation is often obscured at active vents. In such materially connected (Sturkell and Sigmundsson, 2000). very-near-field settings, the onset and evolution of high- The focus of this project is on the northern part of the strain deformation processes, such as crater collapse, are Icelandic rift zone - from Vatnajokull ice cap in the south, particularly ill-constrained. On March 2011, time-lapse across Askja and Upptyppingar volcanoes, and north cameras deployed at the highly-active Pu'u O'o crater, towards Krafla volcano - because of the recently identified Hawaii, imaged a major collapse in unprecedented spatio- magma movements there and the implications for future temporal detail. We analyzed these images with Digital eruptive activity. Image Correlation (DIC) techniques to yield a semi- The aim of this work is to discover how magma is quantitative (pixel-unit) description of the collapse's transported and stored at shallow depth beneath the NVZ in structural development and associated surface Iceland. Seismic studies indicate that there may be several displacements. We then ran numerical pit-crater collapse magma sources even within a single volcanic system in simulations based on the 2D Distinct Element Method Iceland’s NVZ (Soosalu et al., 2009). This work also (DEM) to examine how geometric and mechanical factors directly addresses the question of whether separate volcanic may influence such observations. The time-lapse images systems are linked and, if so, at what depth. reveal initial stability during lava drain-back, followed by The centre of the Askja caldera is sinking (at about 2-5 broad sagging of the crater floor, and then collapse cm per year for the last 40 years) and recent modelling controlled by two ring faults. The structural development suggests that the long-term trend (>20 years) of magma and surface displacement patterns are best reproduced in drainage from beneath this caldera recently reversed, DEM models with a shallow, vertically-elongated magma possibly indicating magma intrusion (Rymer et al., 2010). reservoir, and/or with a host-rock that is reasonably strong Over the same recent period, nearby dormant Upptyppingar at depth. This highlights how new tools like DIC techniques volcano has become seismically active (Jakobsdottir et al., and DEM models can help unravel physical processes at 2008). The question of where the magma is coming from active volcanoes. and going to, and its ultimate fate naturally arises. Results of recent microgravity and Bouguer gravity work will be presented here.

Andrew R. E. B. & Gudmundsson, A. (2008) J. Volcanol. Geotherm. Res. 177: 1045-1054 Dahm, T. & Brandsdottir, B. (2007) Geophys J Int.: 130: 183-192. Einarsson, P. (2008) Jokull 58: 35-58 Rymer, H., Locke, C.A., Ófeigsson, B. G., Einarsson, P & Sturkell, E. (2010) Terra Nova 22(4): 309-313. Jakobsdottir, S.S. et al., (2008) Stud. Geophys. Geod. 52: 513-528 Soosalu et al., S. (2009) Bull. Volcanol. doi:10.1007/s00445-009-0297-3 Sturkell, E. & Sigmundsson, F. (2000) J. Geophys. Res. 105: 25671-25684.

42 VMSG 2013 – Oral Presentation Abstracts

Volcanic unrest in Kenya: A Magmatic systems within satellite perspective sedimentary basins

E. ROBERTSON*1, J. BIGGS1, M. EDMONDS2, C. VYE- N. SCHOFIELD*1, S. HOLFORD2, D. JOLLEY3 BROWN3 1 Earth Sciences, University of Birmingham 1 School of Earth Sciences, Univeristy of Bristol, Bristol, (*[email protected]) BS8 1RJ, UK (*[email protected]) 2 Australain School of Petroleum, Adelaide. 2 Department of Earth Sciences, Univeristy of Cambridge, 3 Geology and Petroleum Geology, University of Aberdeen Downing Street, Cambridge, CB5 3EQ, UK 3 British Geological Survey, Murchison House, West Mains Discerning how magma moves around the subsurface, Road, Edinburgh, EH9 3LA, UK and its connection too sub-aerial volcanic systems is integral to our understanding of how volcanic systems The East African Rift (EAR) system is a 5,000 km long evolve. Our current understanding of magma transit through series of fault bounded depressions that run from the Red the crust is mainly based on petrological and geochemical Sea to Mozambique. The use of InSAR throughout the East methods. These methods have given us great insight, but are African Rift has led to the discovery that a number of unable to give exact geometries of such systems; volcanoes, which haven’t erupted in human history, are additionally they also, in general, cannot take into account actively deforming. In Kenya, the EAR hosts 14 Quaternary movement of magma laterally through the crust. volcanoes that lie along its central rift axis. An initial The use of 3D oil industry seismic data has yielded InSAR study, covering the period 1997-2008, discovered incredible insight into understanding such systems and the that four volcanoes underwent geodetic activity during this ever increasing amount of seismic data available in frontier time. basins containing volcanics means that it is now possible to We present results from a long-term ENVISAT and start to understand magma movement within the subsurface, ALOS PALSAR monitoring campaign of Kenyan Rift and its connection to extrusive volcanism. volcanoes. Using multi-temporal interferograms, we We present a series of examples from basins around the construct time series of ground deformation. We discover world, from both field and seismic data, illustrating key that two Kenyan volcanoes, Silali and Longonot, are aspects of magma flow and eruption within a sedimentary undergoing slow subsidence, at mm rates which single basin. interferograms are unable to detect. We also discover that a third volcano, Paka, has undergone a second period of uplift between 2009-2010 at a rate of 1.6 cm/year. Satellite-based observations play an important role in monitoring and assessing volcanic hazard in this remote region. There is a limited historical record of volcanic activity in Kenya and detailed eruptive records are understudied. We present a remote-sensing study to investigate the temporal and spatial development of volcanic activity at Longonot volcano. Through high- resolution mapping using ASTER, SPOT5 and GDEM imagery, we identify boundaries of eruptive units and begin to establish Longonot’s eruptive history. Understanding the source of the geodetic signal, which may be magmatic, hydrothermal or a combination of both, using both geological and geophysical techniques will aid interpretation of InSAR signals observed elsewhere in the East African Rift and guide future hazard studies across Kenya.

43 VMSG 2013 – Oral Presentation Abstracts

Introduction to John Guest Tribute Contrasting lava flow dynamics and C.R.J. KILBURN*1 morphologies on planetary bodies 1 Aon Benfield UCL Hazard Centre, Dept of Earth Sciences, L. WILSON*1 UCL, Gower St, London WC1E 6BT, U.K. (*[email protected]) 1 Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ. (*[email protected]) This special session is a tribute to the legacy of John Guest (1938-2012). John was a pioneer in volcanology and Lava flow morphology is dictated by magma planetary science. He was among the generation of composition (hence rheology), gas content (explosive or scientists who recognised the importance of transforming purely effusive at the vent), and source conditions (volume volcanology into a physical discipline and vigorously available for eruption; mass or volume discharge rate) and promoted advances in quantifying the effusive behaviour of by the planetary environment into which an eruption occurs volcanoes. In 1973, he led the UK contribution to a ten-year (atmospheric pressure; acceleration due to gravity). Even Anglo-Italian project to investigate the evolution of Mount for the same broad composition (mafic to ultramafic) Etna. The collaboration produced the modern geological expected for the majority of magmas erupted on bodies in map of the volcano and launched a new understanding of our Solar System (Earth's unique subduction zone magmas Etna’s magmatic feeding system and eruptive dynamics. He excepted), the environmental conditions can lead to became one of the first non-US citizens on NASA’s strikingly different products. The Dawn mission to the programme for planetary exploration and joined the science asteroid 4 Vesta, now essentially confirmed as the source of teams for missions to Mercury (Mariner 10, launched in the igneous HED meteorites, together with observations 1973), Mars (Viking, 1975) and Venus (Magellan, 1989). from MESSENGER in orbit around Mercury, have promped He also engaged with the Soviet Phobos mission to Mars an ongoing reappraisal of what we expect to see and what (1988). In 1980, he founded at University College London we actually see as regards lava flow morphologies (Wilson the first NASA Regional Planetary Image Facility outside and Head, 2012; Wilson and Keil, 2012) and the the USA. For his contributions to planetary geology, he consequences of lava flows (Hurwitz et al., 2012 ) on received the 1991 G.K. Gilbert Award from the Geological planetary bodies. Society of America; in the same year, asteroid 1982 HL was Here I summarize some of the more important named Guest by the International Astronomical Union. An systematic results. Every object in the Solar System extended obituary has been published online by the exhibiting mafic volcanism (now or in the past) has a Geological Society of London at: smaller value for the acceleration due to gravity than Earth (granted only slightly so in the case of Venus) and https://www.geolsoc.org.uk/en/About/History/Obituaries%2 lacks/lacked plate tectonics. Crustal stresses and magma 02001%20onwards/Obituaries%202012/John%20Edward% buoyancy both scale with gravity but rock strength does not. 20Guest. Together these factors allow the pre-eruption accumulation of larger volumes of melt than on Earth and encourage greater eruption rates, thus explaining the presence of extensive flood lavas on the Moon, Mercury, Mars and Io. The greater thicknesses of flows on the surfaces of low- gravity bodies encourage heat retention which would itself imply greater flow lengths, other factors being equal. However, provided flows are not volume-limited, maximum flow lengths involve a balance between time for heat loss and time for travel, and flow speed itself depends on flow thicknesss and gravity. I will discuss how these inter-relationships play out in practice.

Hurwitz, D.M., Head, J.W., Wilson, L. and Hiesinger, H. (2012) J Geophys Res - Planets 117 E00H14 Wilson, L. and Head, J.W. (2012) Volcanic eruption processes on Mercury. Lunar Planet. Sci. XLIII, #1316. Wilson, L. and Keil, K. (2012) Volcanic activity on differentiated asteroids: a review and analysis. Chemie der Erde (in press)

44 VMSG 2013 – Oral Presentation Abstracts

The evolution of volcanism in Syrtis Mapping of volcanic terrains across Major Planum (Mars): Drawing the solar system: insight from terrestrial analogues A tribute to John Guest

P. FAWDON*1, M.R. BALME1, C.L. VYE-BROWN 2, D.A. E.R. STOFAN*1 ROTHERY1, C.J. JORDAN3. 1 Proxemy Research, PO Box 338 Rectortown VA 20140 1 Department of Physical Sciences, The Open University, USA (*[email protected]) UK (*[email protected]) 2 British Geological Survey, Edinburgh, UK The Mariner missions to the Moon, Mars, Venus and 3 British Geological Survery, Keyworth, UK Mercury were truly missions of discovery, with great debate in the scientific community over the impact vs. volcanic The Syrtis Major Planum is an Hesperian (3.7 – 3.0 Ga) origin of much of the surfaces of these bodies. The initial low-angle basaltic plains volcano on Mars. The edifice is group of geologists who interpreted these images, including 1500 km by 1100 km, covers 3.6% of the martian surface Don Wilhelms, John Guest and Ron Greeley, pioneered the and has been poorly studied relative to other large martian use of terrestrial geologic mapping techniques to interpret volcanic terrains. This basaltic complex is dissected by these alien surfaces. Recognizing that stratigraphic extensional and compressional fault systems and has two principles could be applied all over the solar system, John distinct central calderas believed to contain evolved Guest produced maps of the surfaces of Mercury, the Moon volcanic products. It is emplaced on, and fringed by, and Mars that are still in use today (e.g., Guest and Greeley, highland cratered terrain containing sites of astrobiological 1983; Greeley and Guest, 1987). significance1. Guest applied his knowledge of mapping of terrestrial We apply a remote sensing approach using modern volcanoes, from Chile to Italy to Hawaii, to provide in depth NASA and ESA data sets of Mars and terrestrial analogue interpretations of volcanic processes across the solar data sets in Afar, Ethiopia and Krafla, Iceland to analyse system. His work on volcanism on Venus (e.g., Guest et surface morphology and composition. We investigate the al., 1992; Guest and Stofan, 1999) demonstrated that volcanic evolution of Syrtis Major Planum using the 3D venusian volcano morphology can be used to discern the visualisation software Geovisionary™ to build an plumbing systems and evolution of these features, and what architectural model of the evolution of the Syrtis Major they imply for the interior evolution of a terrestrial planet. volcanic complex. Guest focused on comparative planetology: how can we use We present initial results of our investigation into the what we learn from studying multiple planetary surfaces to rheological properties of the lava flows on [1] the flanks of better understand the physical process of volcanism. Syrtis Major and [2] terrestrial lavas from Dabbahu (Afar) and Krafla (Iceland). These results are derived from Guest, J.E. and R. Greeley, Misc. Inv. Series I-1408, USGS, morphometric measurements on high resolution (1 m/pix) 1983. DEMs, and a simple rheology model2. We use calculated Guest, J.E. et al., J. Geophys. Res., 97, 15949-15996, 1992. yield strength, viscocity and effusion rate to investigate Guest, J.E. and E.R. Stofan, Icarus, 139, 55-66, 1999. eruption conditions, melting and upper mantle conditions Greeley, R. and J.E. Guest, Misc. Inv. Series, I-1802-B, during the emplacement of Syrtis Major. We will also USGS, 1987. consider, with suitable environmental scaling, rheology derived using the same methrod of terrestial analogues to compare with the results from Syrtis Major. Additionally we present an update on our high resolution mapping at ~15 m/pix, subdividing the previously-recognised unit Hs of Syrtis Major ridged plains3. Within this unit we identify: [1] lava flows 1-6 km wide, 5-30 m thick with flow field lengths up to 500 km that are distributed radially with respect to the central caldera complex.; [2] lava flows with distinct night/day thermal properties cross-cutting Hesperian ejecta containing contributory sinuous channels that might be fluvial in origin; and [3] ‘wrinkle-ridges’ – tectonic features concentric and radial to the central caldera complex; and [4] heavily eroded or buried ‘ghost’ craters. These structural features and DEM analysis1 indicate a total lava thickness of ~500m.

[1] Hiesinger, H., Head, J.W., et al. (2004) J Geophys Res 104 E01004. [2] Moore, H.J., Arthur D.W.G., et al. (1978) Proc Lunar Planet Sci Conf, 9th 3 3351-3378. [3] Greeley, R., Guest, J.E. (1987). Geologic map of the eastern eastern equatorial region of Mars. USGS.

45 VMSG 2013 – Oral Presentation Abstracts

Pulsatory andesite lava flow at John Guest's legacy on Mt Etna: a Bagana Volcano spreading volcano with no magma

G. WADGE*1, S. SAUNDERS2, I. ITIKARAI3 chamber 1 University of Reading, UK. (*[email protected]) JOHN MURRAY*1, 2 Rabaul Volano Observatory, Papua New Guinea. 1 Dept. Environment, Earth & Ecosystems, The Open 3 Rabaul Volcano Observatory, Papua New Guinea. University, Milton Keynes MK7 6AA.

(*[email protected]) Using a time series of TerraSAR-X spaceborne radar images we have measured the pulsatory motion of an The present ground deformation network on Etna is andesite lava flow over a 14-month period at Bagana providing much of the information on how this volcano volcano, Papua New Guinea. Between October 2010 and functions and why. Commissioned by John Guest and first December 2011, lava flowed continuously down the established in 1975 as a precise levelling traverse 11 km western flank of the volcano forming a 3 km-long blocky long across the summit of the volcano, the present network lava flow with a channel, levees, overflows and branches. covers the entire volcanic edifice and comprises 76 km of We captured four successive pulses of lava advancing down interconnected precise levelling lines, more than 100 dual- the channel system, the first such behaviour of an andesite frequency GPS benchmarks, and 27 dry tilt stations. flow to be recorded using radar. Each pulse had a volume of Throughout the 38-year period of monitoring, major the order of 107 m3 emplaced over many weeks. The flank eruptions have consisted of dyke injection episodes, in average extrusion rate estimated from the radar data was which a subsiding trough radiates from the summit to the 0.92 ± 0.35 m3 s-1 , and varied between 0.3 and 1.8 m3 s-1, eruption site, with concomitant outward radial movement of with higher rates occurring earlier in each pulse. This, the lower flanks. together with observations of sulphur dioxide emissions, Between flank eruptions, a similar but distinctly explosions and incandescence suggest a variable supply rate different type of movement takes place. The top 700 metres of magma through Bagana’s conduit as the most likely of the volcano moves towards the sea at rates of about 1 to 3 source of the pulsatory behaviour. cm per year, and the flanks spread outward but not quite radially, those on the western upslope side having a tendency to spread away from a line between the summit and the town of Bronte to the east. Attempts have been made by several workers to model these inter-eruptive movements as inflations and deflations of a subsurface magma chamber, but the modelled amount of volumetric expansion is much smaller than the volume of lava erupted. On Etna there is also little or no subsequent radial contraction that elastic models predict when a magma chamber drains during an eruption. Another peculiarity of deformation between eruptions is that the easterly outward movement increases with distance from the summit, contrary to syn-eruptive dyke injection. Furthermore, different eruptions and different methods give a huge spread of depths for a postulated magma chamber, from 2 km to 30 km in depth. Analogue modelling has provided new insight into this unusual behaviour. Scaled models of brittle cones over an inclined ductile basement show that the pattern of gravitational spreading can be quite different from the radial movement of a level basement. For a basement slope of 1°, the direction and amount of movement closely resembles inter-eruptive deformation at Mt Etna, with the summit moving downhill, lateral spreading occurring on the upslope side, and movement greatest on the lowest downslope flanks. This evidence therefore points to the fact that Etna has no magma chamber, but that magma rises in discrete pulses directly and rapidly from depth, resulting in dykes that reach the surface and erupt, but remain filled with magma that solidifies over a period of weeks and months. This conclusion is in agreement with recent data from seismic tomography and magma residence times.

46 VMSG 2013 – Poster Presentation Abstracts

Geochemistry of Quaternary Eruption chemistry recorded by magmatism in the Greater accretionary lapilli within Caucasus pyroclastic density current deposits,

S. BEWICK*1, N. HARRIS1, I. PARKINSON1, S. ADAMIA2 Kilchrist, Isle of Skye, NW Scotland 1 Earth and Environmental Sciences, Open University, D. BROWN*1, S. DRAKE2, A. BEARD2 Milton Keynes, MK7 6AA. 1 School of Geographical and Earth Sciences, University of (*[email protected]) Glasgow, Gregory Building, Lilybank Gardens, 2 M. Nodia Institute of Geophysics, 1/1 M. Alexidze str., Glasgow, G12 8QQ, UK 0171, Tbilisi, Georgia (*[email protected])

2 Department of Earth and Planetary Sciences, Birkbeck Collision of the Arabian-African and Eurasian plates in College, University of London, Malet Street, London, the Early Miocene resulted in the final closure of the Tethys WC1E 7HX, UK Ocean, crustal thickening, uplift, and magmatism which formed the present day Caucasus orogenic belt [1]. Accretionary lapilli evolution remains controversial. Throughout the Quaternary voluminous magmatism formed Based on field, modelling and rare geochemical studies the Greater Caucasus, the highest peaks in Europe. most workers argue for formation and growth within an Although there are several geochemical studies into related eruption plume, although recent studies suggest formation magmatism on the East Anatolian plateau (Turkey) and the within a pyroclastic density current. Here we adopt an Lesser Caucasus (Armenia and Georgia) [2], the integrated field and geochemical approach to test existing geochemistry, and petrogenesis of Greater Caucasus models of formation. A sequence of massive lapilli tuffs volcanism has not been focus of a modern, systematic and breccias from the Isle of Skye, NW Scotland, record geochemical study. deposition from the sustained passage of a pyroclastic Calc-alkaline to subalkaline magmatism, evolving from density current. Accretionary lapilli in two vertically basaltic-andesites to dacites and minor rhyolites have chemically zoned massive lapilli tuff units within this erupted from the Keli-Kazbegi volcanic centre in northern sequence display evolving chemical trends from core to rim. Georgia throughout the upper Pliocene and Holocene [1, 3]. The accretionary lapilli formed initially as basaltic ash Despite the eruptions occurring on the thickest continental pellets in a co-ignimbrite plume before falling under gravity crust in the region [1], it has been suggested the source is into the underlying density current, where they accreted subduction-enriched lithospheric mantle, with insignificant progressively more evolved laminae. These laminae record input from the continental crust [4]. reverse tapping of a magma chamber with sequential pulses Preliminary results are presented for the petrography of basaltic andesite, andesite and dacite magma being fed and geochemistry from a small selection of samples from into the density current. Accretion of laminae was initially across the same region. Major and trace element bulk rock supported by available moisture and turbulence, but growth data are compared to the limited data from the covering the ceased with the input of dacitic magma and drier conditions. Lesser Caucasus and eastern Turkey [4]. Also presented are The accretionary lapilli were formed within a sustained mineral analyses for Quaternary volcanics from the Greater pyroclastic density current, which demonstrates that Caucasus. Of particular interest is a pyroxene phase present accretionary lapilli are not necessarily formed by simple in some basaltic-andesite samples that contains up to 17wt% fallout from an ash plume. Our model demonstrates that Al O , as well as being rich in TiO . 2 3 2 accretionary lapilli may be used to trace physical and The underlying objective of this work is to compare chemical characteristics of complex eruptions, and petrogenic models for Quaternary magmatism in the Greater understand the magmas which fed those eruptions. Caucasus with that of the Anatolian plateau, and to integrate these findings into a tectonic model for post-collision orogeny in the region.

[1] Adamia et al. (2011) Turkish J. Earth Sci. 20, 1-57 [2] Keskin et al. (1998) J. Volcanol. Geotherm. Res. 85, 355-404 [3] Lebedev et al. (2008) Dokl. Earth Sci., 418, 169-173 [4] Tutberidze (2012) Turkish J. Earth Sci. 21, 799-815

47 VMSG 2013 – Poster Presentation Abstracts

Long-term deformation at Geochemical and petrological Uturuncu volcano in Bolivia and analysis of products from the 2011 igneous diapirism in the crust eruption of Nabro volcano, Eritrea

*1 2 1 R. DEL POTRO*1, M. DÍEZ1, C. MULLER1, J. A. DONOVAN , I. BUISMAN , C. OPPENHEIMER 1 GOTTSMANN 1 Department of Geography, University of Cambridge 1 University of Bristol, School of Earth Sciences, BS8 1RJ, (*[email protected]) Bristol, UK. (*[email protected]) 2 Department of Earth Sciences University of Cambridge

The presence of partial melt in the Earth’s crust causes a The 2011 eruption of Nabro volcano in Eritrea decrease in density, and hence a density contrast, that displaced several communities and produced a lava flow generates a potential field anomaly. Gravimetric techniques over 15km in length along the border between Eritrea and can quantify such an anomaly and invert its signature to Ethiopia. Field investigations took place several months produce a subsurface density distribution model. Here, we after the onset of activity, and over a hundred samples were image 15 km-wide, low-density, vertically-elongated 3D collected and analysed. Whole-rock geochemistry has been structures in the mid-upper crust of the Central Volcanic used to classify the products and compare them to other Zone of the Andes in southern Bolivia. These bodies are rocks from the Afar province. Nabro and Dubbi volcano to massively rooted at the Altiplano-Puna Magma Body the north constitute a transverse alignment relative to the (APMB), and connect it with shallower crustal levels Erta Ale rift zone, and are considerably alkali-enriched beneath the largest Neogene ignimbrite province, the relative to Erta Ale. Altiplano-Puna Volcanic Complex (APVC). Petrological The 2011 eruption was trachybasaltic to trachy-basaltic constraints strongly suggest the presence of a melt fraction andesite in composition, with phenocrysts of olivine, as the cause of the mass deficiency at depth. Moreover, the clinopyroxene, plagioclase, Fe-Ti oxides and minor apatite. partially molten body beneath Uturuncu volcano has caused It appears similar to older mafic eruptions from Nabro. at least 1 meter of ground uplift in no more than 45 years. Older rock samples were also analysed, ranging from Following ground deformation, geological, petrological, primitive basalts to trachytes and rhyolites. Satellite images tectonic and mechanical constraints, we provide evidence and field observations show the presence of large ignimbrite for the diapiric ascent of magma in a region of thickened deposits on the flanks of Nabro, which forms a double continental crust. caldera with Mallahale volcano in Ethiopia. Samples of these are currently being dated, and may represent the caldera-forming eruptions. During the 2011 eruption, dynamic mixing occurred in the shallow conduit between the erupting basalt and an older rhyolite. Our analysis shows that the gas from the basalt was able to bubble through the molten rhyolite, and the two melts mingled at the vesicle rims. This allows for analysis of the mixing process between two melts of diverse compositions. This poster will focus on the 2011 products, describing mineralogy, preliminary insights into eruptive conditions, and the superficial mixing of the magma with the rhyolitic pumice. It will also put this eruption in its local and regional context. Preliminary analysis from older rocks, particularly the ignimbrite, will also be presented.

48 VMSG 2013 – Poster Presentation Abstracts

Magma plumbing and degassing Re-evaluating ‘super’ volcanoes: during the 2008-present summit The case of Yellowstone

eruption of Kīlauea Volcano, B.S. ELLIS*1, D.F. MARK2, M.C. ROWE3, O. Hawai`i BACHMANN1 1 Institute for Geochemistry and Petrology, ETH Zurich M. EDMONDS*1, T. MATHER2, R. MARTIN3, I. SIDES1, (*[email protected]) R. HERD4, D. SWANSON5 2 NERC AIF, SUERC, East Kilbride, Scotland 1 Earth Sciences Department, University of Cambridge, 3 School of the Environment, Washington State University, Downing Site, Cambridge CB2 3EQ, UK Pullman, WA, USA (*[email protected]) 2 Department of Earth Sciences, University of Oxford, UK Yellowstone is commonly held up as the archetypal 3 Department of Geography, University of Cambridge, UK ‘super-volcano’, having had three major eruptive episodes 4 School of Environmental Sciences, University of East at ~ 2 Ma, 1.3 Ma, and 0.6 Ma. However, despite the Anglia, UK importance of such large magnitude events, this idea has 5 United States Geological Survey, Hawaiian Volcano been held up to surprisingly little rigorous testing. Here we Observatory, Hawai`i 96718, USA combine new high-precision Ar/Ar geochronology and mineral chemistry from multiple phases to shed new light The 2008-current eruption of Kīlauea Volcano is the on the explosive history of the Huckleberry Ridge (HRT) first explosive eruption to occur at the summit since 1924, and Lava Creek (LCT) eruptions from the Yellowstone and offers a unique opportunity to test models of degassing volcanic field. 40 39 and magma plumbing. We measured sulphur dioxide (SO2) Recent high precision Ar/ Ar geochronology has and carbon dioxide (CO2) concentrations in the gas plume shown that member C of the HRT was erupted at least 6,000 from Halemau`ma`u using electrochemical and non- years later than members A and B. This result is supported dispersive infrared sensors in April 2009. We analysed by differences in the compositions of fayalitic olivine, olivine-hosted melt inclusions from tephra erupted in 2008 augite, sanidine and quartz between the members. Mafic and 2010 for major, trace and volatile elements. The gas and minerals are compositionally homogeneous with augites and melt data are both consistent with a relatively evolved fayalites of member C less magnesian than those found in magma batch which equilibrated at depths of 1.2-2.0 km members A and B. Quartz grains show a variety of textures beneath Halemau`ma`u prior to the current eruptive activity. in CL imaging and have within-grain variations in titanium The differences in the volatile concentrations between the (determined via EMPA and LA-ICPMS) of up to a factor of melt inclusions and matrix glasses are consistent with the 2. Again, member C of the HRT has distinct compositions observed gas composition, indicating that there is no need to of quartz (with higher Ti) than earlier erupted HRT. Quartz invoke either addition of CO2 vapour, or scrubbing of SO2. from LCT shows differences between members A and B

A slight enrichment in SO2 in the gas over that calculated with member A having generally lower Ti (avg. 55 ppm) from the melt compositions is consistent with the than member B (avg. 102 ppm). Pb isotopes in sanidine decomposition of sulphides during magma decompression further confirm the difference between members A and C of and degassing, thereby buffering melt sulphur the HRT and between members A and B of the LCT. concentrations. The degassing of sulphur and halogen gases Combining high-precision geochronology and detailed from the melt requires low pressures and therefore we mineral-scale geochemistry from a number of different invoke convection to bring the magma close to the surface phases provides a robust method of distinguishing to degas, before sinking back into the conduit. The fluxes of individual magma batches and clarifying the explosive gases (900 and 80 t/d SO2 and CO2) are used to estimate history of a volcano. Our new data suggest that in some convective magma fluxes (1.2-3.4 m3/s). The observation of cases ‘super-eruptions’ might be better thought of as a minimal loss of hydrogen from the melt inclusions implies a series of large eruptions over a short timespan rather than a rapid rise rate (less than a few hours), which constrains the single gigantic event. conduit radius to 1-2 metres (or a narrow dyke with a similar cross-sectional area). The inferred conduit radius is much narrower than the lava lake at the surface, implying a flared geometry. The melt inclusion data suggest that there is a progressive decrease in melt volatile concentrations with time during 2008-2010, consistent with convection, degassing and mixing in a closed, or semi-closed magma system. Our results are consistent with ground deformation (INSAR), thermal observations (of magma movement, gas pistoning and bubble bursting) and seismicity (source of long period earthquakes).

49 VMSG 2013 – Poster Presentation Abstracts

Hydrothermal cells and the 2011-2012 eruption of Nyamuragira thermal boundary layer around the M. FAZIO*1, A. JONES1, A. BEARD2 Cuillin Gabbro, Isle of Skye 1 Earth Sciences, University College London (*[email protected]) F. ENTWISTLE*1, B. YARDLEY1, A. BOYCE2 2 Birkbeck College London 1 University of Leeds (*[email protected]) 2 SUREC Between 6/11/2011 and 25/1/2012 a new fissure eruption occurred at Nyamuragira Volcano (Democratic Fluid circulation and associated thermal regimes are Republic of Congo)1. In this study we show new rock crucial to understanding geothermal systems. Thermal samples (provided by Abigail Church, former UCL PhD) boundary layers provide the connection between geothermal coming from this event (that are now being studied) along systems and the intrusive heat source and it is these thermal with new specimens from the neighbouring volcano, boundary layers that are now the focus for the exploration Nyiragongo, which last erupted in 2002. Though they are of Enhanced Geothermal Systems (EGS). EGS focus on just 15 km far from each other, their current bulk high enthalpy systems with the fluids being supercritical. compositions are quite different ranging from nephelinite – Heat removed by water circulation around the intrusion melilitite - leucitite on Nyiragongo2 to tephrite – basanite - is transferred by conduction from the magma through a phonolite on Nyamuragira3. thermal boundary layer, so that the more active the We will mainly focus on the volatile contents, analyzing geothermal convection the thinner this layer must be. the melt inclusions in dry minerals, to characterize the Thermal boundary layers are preserved as high grade magma source. On Nyamuragira this type of study has been metamorphic aureoles, in this case categorised by the conducted recently by Head et al.4, but it does not account presence of 2 pyroxene hornfels in the inner aureole, for the last eruption, while on Nyiragongo the last melt moving outwards into an amygdaloidal rich zone dominated inclusions analysis was run more than twenty years old5, by chlorite, epidote and actinolite with the most distal parts well before the 2002 eruption, the last one after the famous of the aureole containing amygdales containing zeolites. We 1977 event. propose that the inner hornfelses of the Skye aureole Due to tens of years of internal crisis, the North Kivu represent a thermal boundary layer while the rocks outside region, where both volcanoes lie, is one of the most this zone have experienced hydrothermal alteration in a dangerous area in the world. This explains the paucity of geothermal field. Areas of the contact where the hornfelses research. In an attempt to overcome the difficulty to carry are thickest correspond to limited geothermal circulation, on a fieldtrip, we found a clear resemblance between the while where the hornfelses are thinnest geothermal activity rocks of both DRC volcanoes6-4and some of those at Vulture was at a maximum. volcano (Italy)7. For example, they share similar TAS

Two distinct zones have been identified around the diagrams and K2O/NaO ratios. Cuillin gabbro; the widespread geothermal field dominated The possibility to compare rock samples with similar by convective heat transfer with large fluid fluxes and chemical compostions allows us to run experiments to categorised by greenschist facies metamorphism. This zone understand the rheology of lavas emitted by both volcanoes, is separated from the intrusive heat source by a (highly and its dependance on chemical compositions and volatile variable) high temperature zone of recrystalisation; contents. Note that the rheological properties of these lava representing a thermal boundary layer which is dominated were investigated just once by Giordano et al.8 who took by conductive heat transfer, minimal amounts of fluid flow account only of the highly fluid lavas of Nyiragongo. and categorised by the presence of 2 pyroxene hornfels. This thermal boundary layer varies enormously around the [1] Volcano Discovery [homepage on the internet]. (cited aureole with minimum thicknesses ranging from 2m up to 2012 Jan 27). [about 1 screen]. Available from: 150m at different locations around the aureole. http://www.volcanodiscovery.com/view_news/4622/Ny The thermal structure implied by the mineral zonation amuragira-volcano-DR-Congo-update-eruption- appears to be at odds with current interpretation of oxygen continues-with-active-lava-lake-and-lava-flow-from- stable isotope analysis. The classic work of Taylor and new-.html Forester (1971) and Forester and Taylor (1977) reported [2] Platz, T., Foley, S.F., Andre, L., (2004) J. Volcanol. depleted δ 18O values from the Cuillin gabbro and the Geotherm. Res. 136, 269–295. [3] Aoki, K., Yoshida, T., Yusa, K., Nakamura, Y., (1985) surrounding aureole, with the lightest values in both cases J. Volcanol. Geotherm. Res. 25, 1–28. close to the contact, and interpreted the depletion as the [4] Head, E. M., Shaw, A. M., Wallace, P. J., Sims, K. W. result of circulation of meteoric water. Current stable W., Carn, S. A., (2011) Geochem. Geophys. Geosyst. isotope analysis indicates that the lightest values are in fact 12, Q0AB11, doi:10.1029/2011GC003699. those that have the highest degree of hydrothermal [5] Bailey, D.K., Hampton, C.M. (1990) Lithos 26, 157- alteration, but with light values for samples from the 165. thermal boundary layer. The challenge is to evaluate the [6] Chakrabarti, R., Basu, A. R., Santo, A. P., Tedesco, D., relationship between oxygen isotope depletion and Vaselli, O., (2009) Chem. Geol. 259, 273–289. temperature and thereby develop a more sophisticated [7] Beccaluva, L., Coltorti, M., Di Girolamo, P., Melluso, model for the palaeogeothermal activity, and second to L., Dilani, L., Morra, V., Siena, E., (2002) Miner. and understand the mechanisms by which high temperature Petr. 74, 277–297. assemblages have experienced extensive modification of [8] Giordano, D., Polacci, M., Longo, A., Papale, P., their oxygen isotope composition without displaying any Dingwell, D. B., Boschi, E., Kasereka, M., (2007) macroscopic features of related hydrothermal activity.. Geophys. Res. Lett. 34, L06301.

50 VMSG 2013 – Poster Presentation Abstracts

Petrological constraints on deep Silicic volcanism in the Main degassing prior to large basaltic Ethiopian Rift: A case study of

fissure eruptions: CO2 in Laki melt Alutu Volcano inclusions W. HUTCHISON*1, J. BIGGS2, T. MATHER1, D. PYLE1, G. 3 YIRGU M.E. HARTLEY*1, J. MACLENNAN1, M. EDMONDS1, T. THORDARSON2, D.J. MORGAN3 1 Department of Earth Sciences, University of Oxford, UK (*[email protected]) 1 Department of Earth Sciences, University of Cambridge 2 Department of Earth Sciences, University of Bristol, UK (*[email protected]) 3 2 School of GeoSciences, University of Edinburgh Department of Earth Sciences, University of Addis Ababa, 3 School of Earth and Environment, University of Leeds Ethiopia

The Main Ethiopian Rift is lined by a series of regularly The Laki eruption of AD 1783 produced over 15 km3 of spaced silicic volcanic complexes, typically 10-20km in basaltic lava and tephra, and led to three years of extreme climatic variability in Europe and North America. We have diameter. While most of these complexes show signs of used a novel combination of micro-analytical measurements large caldera forming eruptions in the recent past, little is known of how active these volcanoes are currently and what to constrain the history of deep-degassing CO loss from the 2 the frequency and magnitude of past eruptions has been. Laki magma prior to eruption. The data provide important Our work will address these issues via a detailed multi- constraints on magma storage depths and the overall CO 2 diciplinary case study at Alutu volcano. Alutu, identified in budget of the eruption, and have implications for the interpretation of seismic, geodetic and gas monitoring data the recent Global Facility for Disaster Risk Reduction from regions where large fissure eruptions occur. (GFDRR) of the World Bank [Aspinall et al., 2011] as a ‘high-risk’ volcano, has shown clear signs of unrest, We have analysed volatile, trace and rare earth elements undergoing large pulses of uplift in 2004 (15cm) and 2008 by SIMS in over 100 naturally-quenched, olivine-hosted (10cm) [Biggs et al., 2011]. We are assessing the current melt inclusions from Laki. Raman spectroscopy was then state of activity at Alutu by both ground deformation used to determine the fluid density, and hence the CO2 content, of bubbles in the melt inclusions. Bubbles are (InSAR and continuous GPS), as well as volcanic degassing (portable CO gas analyzer). Our knowledge of the common in the Laki melt inclusions, and formed when post- 2 historical activity of Alutu will be developed via a entrapment crystallisation within an inclusion causes CO to 2 combination of geological field mapping as well as remote exsolve from the melt. It has previously been assumed that sensing from satellite (ASTER) and airborne data (LiDAR the amount of CO2 in shrinkage bubbles is negligible. We imagery). have added the CO contained in the bubble to the glass 2 Our initial field mapping and geochemical analysis CO2 content, to obtain the total CO2 of the Laki melt inclusions, which range from volatile-rich (4000-8000 ppm found that previous eruptions at Alutu have produced a large compositional range of volcanic products from mildly total CO ) to almost completely degassed (<50 ppm total 2 alkaline basalt through to peralkaline rhyolite (spanning 52- CO ). Bubbles typically comprise <5 vol.% of the melt 2 74% SiO ). We identified previously unrecognised inclusion, but contain ~90% of the total CO . The 2 2 explosive activity (fallout and pyroclastic flow deposits), as combination of SIMS and Raman analyses can thus be used to significantly improve estimates of melt inclusion well as evidence of mass flows (lahars). The youngest entrapment pressures and quantification of the total mass products of Alutu are a series of obsidian lava flows, often these align with faults, and potentially trace out an older flux of volatiles associated with Laki. ring-fracture system, linked to an earlier caldera forming Solubility models for CO in basaltic melt can be used 2 event. to predict the degassing path of the Laki magma for Results of the CO degassing show that fluxes vary different crystallisation models. Carbon is expected to 2 between low background values of 0.1 g(CO )m-2day-1, on behave as an incompatible trace element similar to La or Nb 2 the rift floor away from the volcano, to 2400 g(CO )m-2day-1 in a CO -undersaturated melt. CO /Nb ratios can thus be 2 2 2 immediately above active faults on the volcano. The results used to deconvolve the effects of crystallisation and show that volcanic fractures, likely inherited from an earlier degassing. Laki melt inclusions hosted in Fo olivines 83-86 caldera forming event, as well as rift related faulting impart have the highest CO concentrations and CO /Nb ratios, 2 2 significant controls on the degassing pattern. indicative of entrapment during the deep crystallisation of a These measurements will offer some of the first CO2-undersaturated magma. By contrast, melt inclusions hosted in Fo olivines have low CO and CO /Nb, detailed constraints on the eruptive history and current 71-76 2 2 activity of a Main Ethiopian Rift volcano. Through these indicative of entrapment during crystallisation at a shallow new data we hope to contribute to the assessment of level in the crust. The melt inclusions thus appear to record volcanic hazard at Alutu, and more generally, to expand our concurrent crystallisation and degassing in the Laki magma. knowledge of the role these silicic volcanic centres play in We use solubility models to constrain the melt inclusion continental rifting processes. entrapment depth, and estimate the total CO2 loss from the Laki magma. Aspinall, W., et al. (2011) Volcano Risk Study 0100806-00- Further work will investigate the timescales of 1-R. degassing in the Laki magma system, and used to estimate Biggs, J., et al. (2011) Geochemistry Geophysics the potential flux of CO to the surface in the premonitory 2 Geosystems 12, 1-11. phases of the Laki eruption.

51 VMSG 2013 – Poster Presentation Abstracts

Modelling of magmatic Magma mixing, storage and hydrothermal systems: Phlegrean degassing during the 1959 Kīlauea Fields case study Iki eruption, Hawai`i

A. JASIM*1, F. WHITAKER F.2, A.C. RUST2 I. SIDES*1, M. EDMONDS1, J. MACLENNAN1, B. HOUGHTON2, D. SWANSON3 1 School of Earth Sciences, University of Bristol (*[email protected]) 1 Earth Sciences Department, University of Cambridge, 2 School of Earth Sciences, University of Bristol Downing Site, Cambridge CB2 3EQ, UK (*[email protected]) In the last few decades the importance of the 2 Dept. of Geology & Geophysics, University of Hawaii, hydrothermal system in the behaviour of volcanoes has been Honolulu, Hawaii, USA increasingly recognised. There are several aspects that make 3 Hawaiian Volcano Observatory, United States Geological the hydrothermal system important and interesting to Survey, Hawaii Volcanoes National Park, HI 96718, investigate: i) it is extremely sensitive to perturbation from USA magmatic processes; ii) some of the ground deformation attributed to magmatic process could be simply related to We present a study of magma mixing and volatile hydrological phenomena; iii) the chemical reactions degassing during the 1959 Kīlauea Iki eruption (Hawai`i), between circulating hot water and country rock change the which was associated with a well-characterised sequence of physical properties (e.g. porosity, permeability, strength) of high fountains. Olivine-hosted melt inclusions from tephra the rocks and thereby affect the response of the volcano to associated with episodes 1-3, 5-8, 10 and 15-16 were meteoric precipitation, degassing and ground deformation. analysed for major, trace and volatile elements. The trends Here we present preliminary results of numerical in the melt inclusions are consistent with changes in modelling of the Phlegrean Fields, exploring the importance eruption parameters and we propose they record syn- of heterogeneous rock properties in controlling eruptive geochemical changes in melt composition. The hydrothermal fluids circulation. Fluid and heat flows are melt inclusions show a trend of decreasing MgO content modelled using TOUGH2 which simulates non-isothermal through episodes 1 to 16, and the host olivine compositions multicomponent and multiphase flows in porous and become less forsteritic with time. Trace element fractured media (Pruess, 1991). We simulate fluid flow and concentrations in melt inclusions and glasses show that both heat transport in a 2D radial model, centred on a fumarole. mixing of heterogeneous mantle melts and fractionation The model domain is 1.5 km deep with a radius of 10 km, must be operating to produce the range in magma with three main geological units representing the pyroclastic compositions. The melt inclusions record changes in the rocks, underlain by the Yellow tuff formation and the volatile content of the melts with time, becoming poorer in

Chaotic tuffites formation (post-caldera deposits). H2O as the eruption proceeded. The CO2 concentration of Additionally there is a system of circular faults that the melt inclusions correlates negatively with fountain dislocates the units. The system is water saturated, there is a height; whereas H2O shows no correlation with fountain constant heat source at the base of the model and a water height. The CO2 concentration of the melt inclusions input at the base of the fumarole (based on Todesco et al, correlates positively with the Mg# of the matrix glass. We 2010). The system is closed to fluid flow along the base and propose a model whereby drained-back lava mixes with the side, and the top boundary condition is maintained at both summit-stored, and more primitive magma from depth, atmospheric pressure and temperature. Initial conditions are causing an overall decreasing melt H2O content with time. 4 defined by a pressure gradient of 1*10 Pa/m (hydrostatic Primary magmas supply volatile-rich melts carrying CO2 pressure) and a temperature gradient of 0.13 C/m vapour. The proportion of CO2 over H2O in the melts has a calculated from well data (Rosi & Sbrana, 1987). direct impact on fountain dynamics: the higher the fraction

Prelimary results reveal the strong connection between of CO2 in the gas mixture, the lower the lava fountain, due rock properties, fluid flow and heat flux. The development to the higher density of CO2 over H2O at a fixed of convective cells can be inhibited with a small change in temperature and pressure. the distributions of rock properties, even keeping constant all the other paramaters, suggesting that discontinuites (e.g. faults) may play a key role in the fluid distribution. The model that is currently running shows a more complex geometry and it aims to understand the role of faults in driving fluid flow in a volcanic caldera setting.

Todesco, M., (2010) Journal of Geophysical Research Vol 115, B09213. Pruess, K., (1991) TOUGH2, Lawrence Berkeley National Laboratory. Rosi, M., (1987) CNR Quaderni de “La ricerca scientifica” Vol 114.

52 VMSG 2013 – Poster Presentation Abstracts

Post-caldera explosive activity at Compositional heterogeneity of the Furnas volcano, São Miguel, Azores Earth’s convecting mantle:

A. J. JEFFERY*1, R. GERTISSER1, B. O’DRISCOLL1, A. Constraints from olivine-hosted PIMENTEL2, J. M. PACHECO2, S. SELF3 melt inclusions from a continental 1 School of Physical and Geographical Sciences, Keele flood basalt setting University, Keele, Staffordshire, ST5 5BG, UK. (*[email protected]) E.S. JENNINGS*1, S.A. GIBSON1, J. MACLENNAN1, R.N. 2 Centro de Vulcanologia e Avaliação de Riscos THOMPSON2 Geológicos, Universidade dos Açores, 9501-801 Ponta 1 Deptartment of Earth Sciences, University of Cambridge, Delgada, Açores, Portugal UK (*[email protected]) 3 Department of Earth and Environmental Sciences, The 2 Department of Earth Sciences, University of Durham, UK Open University, Walton Hall, Milton Keynes, MK7 6AA, UK Picrites and ferropicrites from the Early-Cretaceous

Parana-Etendeka Large Igneous Province are primary Furnas volcano is the easternmost of three active central mantle melts associated with the initial impact of the proto- volcanoes on the island of São Miguel, Azores. Tristan mantle plume. These high temperature melts provide Approximately 3000 people live within the nested Furnas an excellent opportunity to assess compositional caldera, and several thousand more are within the heterogeneity of the convecting mantle. Ferropicritic melts immediate vicinity [1]. The volcano’s eruptive history are especially interesting; they are rare on the Earth's comprises a range from effusive, dome-forming activity to, surface, and are documented only as small-volume dykes at least, two explosive, caldera-forming events involving and flows at the base of continental flood-basalts. They are pyroclastic density currents (dated at ~30,000 and ~12,000 characterised by high FeO (>~13 wt %) and low Al2O3 (< 14C y B.P.) [2]. The younger eruptive history has ~10 wt %), with very steep REE profiles ([Gd/Yb]N = 2- predominantly been characterised by sub-plinian style 3.5), and experiments show that they originate from a garnet activity. Ten post-caldera eruptions (Furnas A-J [2, 3]) pyroxenite source. occurred at Furnas within the past 5000 years, producing a Olivine-hosted melt inclusions preserve instantaneous total of ~0.9 km3 (DRE) of magma. The youngest of these melt compositions, and therefore are key to observing initial (Furnas J), occurred in A.D. 1630, after human settlement melt composition prior to overprinting by mixing, of the island. The deposits comprise interbedded fine ash crystallisation and assimilation processes. We have and pumice lapilli beds that overlie the widespread Fogo A analysed experimentally-quenched olivine-hosted melt tephra from nearby Fogo volcano, forming the Upper inclusions for trace elements using SIMS and have Furnas Group (UFG) [2, 3]. Three UFG eruptions (Furnas combined this data with mineral chemistry to make a E, I, J) produced lava domes following intial explosive preliminary assessment of their mantle source phases [1]. characteristics and melt evolution. Lithospheric Here, we present new whole-rock major and trace contamination evident in whole-rock chemistry is absent element data, alongside mineral chemical data, for the from most melt inclusions in picrites, but crustal products of the UFG as well as the Povoação Ignimbrite, contamination is clearly present in a small subset, with associated with the formation of the older Furnas caldera. combined enrichments in Rb, Ba and Sr. Picrites show a Whole-rock compositions are comenditic trachyte with a greater range in all elemental concentrations in the olivine- limited SiO range from 62-63 wt. % and agpaitic indices 2 hosted melt inclusions relative to whole rock analyses e.g. between 0.73-1.13. Mineral assemblages include [La/Lu]N = 1.5-3 (whole rock); = 0.9-4 (melt inclusions). anorthoclase, clinopyroxene, Ti-magnetite and occasional Ferropicrite olivine-hosted melt inclusions have more biotite and ilmenite. Cognate syenite nodules within the diverse chemistries, with a large range in LREE slopes and Furnas J deposits contain anorthoclase, clinopyroxene, variably contaminated overprints. Zoned clinopyroxene amphibole and oxides. Whole-rock REE patterns display phenocrysts in some ferropicrite samples also indicate the enrichment of LREE, and, with the exception of the involvement of more complex petrogenetic processes. Povoação Ignimbrite, a pronounced negative Eu anomaly (Eu/Eu* = 0.15), as well as minor fractionation between MREE and HREE. Major and trace element data suggest that the trachytitic magmas are formed predominantly by fractional crystallisation from Furnas basalt. Uniform comenditic trachyte has been erupted from Furnas for several thousands of years, implying a long-lived, evolved magma system capable of producing substantial explosive eruptions. An improved understanding of the longevity and dynamics of this magma system has implications for future hazard assessment.

[1] Cole et al. (1999) J Volcanol Geotherm Res 92, 39-53 [2] Guest et al. (1999) J Volcanol Geotherm Res 92, 1-29 [3] Booth et al. (1978) Phil Trans Royal Soc London 288, 271-319

53 VMSG 2013 – Poster Presentation Abstracts

Tracking changes of magma Timescales of magmatic processes at transfer beneath Mt. Etna: Mt. Ruapehu, New Zealand: linking Evidence from crystal zonation and mineral diffusion rates to real-time gas monitoring monitoring data

M. KAHL*1,2, S. CHAKRABORTY1, F. COSTA3, M. GEOFF KILGOUR1*, KATE SAUNDERS1, JON BLUNDY1, POMPILIO4, M. LIUZZO5, M. VICCARO6 HEIDY MADER1 1 GMG, Ruhr-University Bochum, Germany 1 School of Earth Sciences, University of Bristol. 2 SEE, The University of Leeds, UK (*[email protected]) (*[email protected]) 3 EOS, Nanyang Technological University, Singapore Mt. Ruapehu is an andesite cone volcano situated at the 4 INGV- Sez. di Pisa, Italy southern end of the Taupo Volcanic Zone, New Zealand. 5 INGV- Sez. di Palermo, Italy Active vents are submerged beneath a warm, acidic crater 6 Università di Catania, Italy lake (~ 0.2 km2) that exhibits a thermal cycle between 12 and 40 °C. The presence of Crater Lake causes the eruption Tracking the pre-eruptive storage and transfer of style to be dominantly phreatic or phreatomagmatic. magmas beneath highly active volcanoes, such as Mt. Etna Historical eruptions at Ruapehu were typically small (Sicily), is one of the goals of modern volcanology Here we volume (< 0.001 km3) eruptions that effected the summit show an integrated methodology linking compositional and plateau. Larger eruptions ejected material to > 200 km from temporal information recorded in chemically zoned olivines the vent. Scoria samples available for this study were with real-time variations (CO2/SO2) in gas emanations in erupted in 1969, 1971, 1977, 1995, and 1996. order to monitor the intermittent input of new magma into The monitoring network at Ruapehu has consisted of sections of Mt. Etna’s plumbing system. We illustrate our quasi-monthly Crater Lake temperature and fluid chemistry approach using the 2006 summit eruptive period of Mt. measurements, and seismic monitoring since the mid- Etna. We have used data on compositional zoning of olivine 1960’s. A more modern network was installed during and in combination with real-time degassing data obtained immediately after the last major eruption in 1995-1996, during the period January 2005 – December 2006 [1] to including regular airborne and fluid chemistry show how variations in the monitoring signals can be measurements and telemetered broadband seismic data. related to changes occurring within the plumbing system at Historical eruptions have been preceded by short-term depth. The investigated eruptive products (July & October seismic precursors and/or fluid chemistry changes. Prior to 2006) contain olivines with different populations of core some eruptions, a period of increased seismicity has and rim compositions (Fo70-72; Fo79-82; Fo73-75) and occcured days to weeks before the event making Ruapehu a zoning patterns. We explain the diverging compositional very difficult volcano to predict. Here we present mineral and zoning record as the product of magma evolution in at diffusion data on zoned pyroxene phenocrysts and least three distinct environments (labeled M0, containing microlites in order to constrain the magmatic processes that olivine of Fo79-82; M2 with Fo70-72 and mm1 with Fo73- occurred soon before each eruption. 75) with melt transfer and mixing between them. Modeling Recent petrological data has suggested that individual the diffusive relaxation of the compositional zoning profiles magma batches at Ruapehu interact with other magmas enabled us to constrain the time the crystals (+ their and/or crystal-mush zones during ascent resulting in associated melts) spent in transit between these common crystal (and melt) exchange. In some instances, environments. We can show that the systematic rise of the scoria erupted include phenocrysts (clinpyroxene, degassing signal (CO2/SO2) [1] can be related to the gradual orthopyroxene, and plagioclase) that are all foreign to the (pre- and syn-eruptive) supply of batches of mafic magma host melt, implying that a crystal-poor melt intruded into a into segments of the plumbing system, where mixing with crystal-mush zone shortly before eruption. In particular, residing (more evolved) magma was promoted. The clinopyroxene crystals exhibit common reverse-zoning (Fe- temporal details of magma supply suggest that some of this rich to Mg-rich) on the outermost margins of the phenocryst new input of mafic magma may have triggered the initiation (and microlite). We note that a thin (~2-4 µm) Mg-rich rim of different eruptive cycles (July, August). is common to most pyroxene phenocrysts and microlites. We interpret these rims to represent a period of heating [1] Aiuppa et al., (2007) Geology 35, 1115-1118. immediately prior to eruption. Using published Fe-Mg diffusion exchange coefficients for clinopyroxene, we show that the outermost rims record a heating event a matter of weeks before all eruptions analysed. These data are compared to Crater Lake chemistry and seismic data to provide a comprehensive account of the magmatic- hydrothermal system response to magma-magma and magma-mush interactions.

54 VMSG 2013 – Poster Presentation Abstracts

Disequilibrium during volcanic Melting events in the Rum layered eruption: effect of cooling rate on intrusion plagioclase-liquid element exchange J. LEUTHOLD*1,2, J. BLUNDY1, M. HOLNESS2 M. KLÖCKING*1, M. EDMONDS1, M.C. S. HUMPHREYS2 1 School of Earth Sciences, University of Bristol. (*[email protected]) 1 Department of Earth Sciences, University of Cambridge, 2 Department of Earth Sciences, University of Cambridge. Downing Street, Cambridge, CB2 3EQ (*[email protected]); The Rum Eastern Layered Intrusion (RELI) Unit 9 is 2 Department of Earth Sciences, University of Oxford, South composed of peridotite with poikilitic Plg and Cpx, Parks Road, Oxford, OX1 3AN, UK troctolite with interstitial Cpx and eqigranular gabbro.

Gabbro enclaves occur within troctolite. Cpx rims are Geothermobarometry is widely applied to volcanic poorly developped in layered peridotite and troctolite and rocks, based on the equilibrium distribution of elements bulk rock analyses display distinct Eu positive anomalies, between melt and crystals. However, often the rapid ascent evidencing loss of interstitial liquid. Cpx rims are Cr-poor, of magmas means that equilibrium cannot be maintained REE-rich and display low La/Lu (strongly under the rapidly changing temperature and pressure incompatible/moderatly incompatible elements) ratio in conditions. This results in errors in the results of common regard to associated cores. Troctolite is overlain by gabbro, thermometers and barometers that are as yet largely separated by a wavy horizon. Gabbro Cpx show discrete unquantified. reverse Cr and REE zoning and a constant high La/Lu ratio. We assess temperatures obtained with the plagioclase- Troctolite interstitial Cpx and gabbro equigranular Cpx liquid thermometer [1] and the degree of disequilibrium for progressively get oikocrystic towards the northern edge of a range of rocks with different eruption rates erupted from an intrusive peridotite sill, forming poikilitic gabbro, with Volcán de Colima, Mexico, and Soufrière Hills Volcano, Cpx oikocrysts. Cpx Cr-rich (~1.1 wt% Cr O ), REE- Montserrat. We compare major element compositions 2 3 moderate, high La/Lu anhedral core enclose randomly measured in plagioclase and glass by electron microprobe to oriented small (up to 0.5 mm) Ol and Plg inclusions. They theoretical models of magma evolution [2], assuming that are overgrown by a Cr-moderate (~0.7 wt% Cr O ), REE- the degree of disequilibrium in plagioclase increases with 2 3 poor, high La/Lu anhedral core. Cpx dissolution occurs cooling rate [3]. Cooling rate is independently estimated along inclusions. Poikilitic rims are Cr-poor (~0.2 wt% using crystal size distribution and other textural features. In Cr O ), REE-rich and display low La/Lu ratio. They enclose addition, the clinopyroxene-liquid thermometer is applied to 2 3 large (1 mm) oriented Plg and Ol crystals. The rim Colima rocks to test the validity of different temperature thickness increases from the Unit 9 base to the top. The Cpx models. We also quantify Fe and Mg concentrations in rim crystallization is synchronous with cumulate pile plagioclase phenocryst rims, and attempt to quantitatively compaction. deconvolve the effects of heating by mafic recharge and Equilibrium liquids were estimated using Wood and latent heat of crystallisation from disequilibrium caused by Blundy (1997) partition coefficients. The liquid at the origin quenching. The data from Colima and Montserrat are of the peridotite, troctolite and poikilitic gabbro Cpx cores compared to petrological data from other andesitic arc display a higher La/Lu ratio than the corresponding rims volcanoes compiled from the literature. and the picritic dikes. The high La/Lu ratio of the liquids in

equilibrium with the Cpx cores is interpreted as a signature [1] Putirka K., (2008) Reviews in Mineralogy and of low degree partial melting. Cpx cores is best explained Geochemistry 69, 61–120. by 5% partial fractionated melting of a gabbroic assemblage [2] Gualda G.A.R., Ghiorso M.S., Lemons R.V., Carley (RELI interstitial crystals or gabbro). Gabbro enclaves T.L., (2012) Journal of Petrology 53, 875-890. within troctolite are relics. The multiple generations of Cpx [3] Mollo S., Putirka K., Iezzi G., Del Gaudio P., Scarlato are witnesses of succesive melting episodes. Cpx rims are P., (2011) Lithos 125, 221–235. best explained by partial melting (5%) of a gabbroic

assemblage, mix with picritic liquid (30-50%) and subsequent Rayleigh fractional crystallization (F = 1-0.7). Known RELI liquids (Upton et al., 2002) fail to model crystallization of the Unit 9 Cpx cores by simple fractional crystallization. We suggest that the Unit 9 gabbro crystallized from aggregated drops from a partially molten gabbroic assemblage deeper in the RELI. Subsequent intrusion of peridotite sills induced partial melting of the Unit 9 gabbro. Once porosity was sufficient, differentiating liquids from the peridotite percolated throughout the crystal mush pile, mixing with interstitial liquid and crystallizing the interstitial crystals. Thus the composition of the percolating liquid and the final metasomatized cumulate differ from simple fractionation products along the Rum liquid line of descent.

Wood, B.J., Blundy, J.D. (1997) CMP, 129, 166-181. Upton, B.G.J et al. (2002) Geol. Mag., 139, 437-452.

55 VMSG 2013 – Poster Presentation Abstracts

The origin of the Igwisi Hills An integrated study of SO2 kimberlite (Tanzania) constrained degassing from Tungurahua from He and O isotopes volcano, Ecuador

F.R. MARKS*1, F.M. STUART2, R.W. BROWN3 B. MCCORMICK*1, J. YANG2, M. EDMONDS1, T. 3 4 5 6 1 MATHER , S. CARN , S. HIDALGO , B. LANGMANN , M. Geographical & Earth Sciences, University of Glasgow, 2 Glasgow G12 8QQ, UK (*[email protected]) HERZOG 2 Isotope Geosciences Unit, Scottish Universities 1 Department of Earth Sciences, University of Cambridge; Environmental Research Centre, East Kilbride G75 (*[email protected]) 0QF, UK 2 Department of Geography, University of Cambridge; 3 Department of Earth Sciences, Durham University, 3 Department of Earth Sciences, University of Oxford; Durham DH1 3LE, UK 4 Department of Geological and Mining Sciences and *Now at: UCD School of Geological Sciences, Science Engineering, Michigan Technological University; Centre West, University College Dublin, Belfield, 5 Dublin 4, Ireland Instituto Geofisico, Escuela Politécnica Nacional; 6 Institute of Geophysics, University of Hamburg. Despite decades of study, the depth and source of kimberlite melts remains enigmatic. The isotopic Tungurahua is a 5023 m-high stratovolcano in Ecuador, composition of volatile elements, supply unique information with an estimated long-term mean SO2 output of 1458 ± on the melt sources in mantle-derived rocks. However, 2026 t/day. Gas emissions from Tungurahua are most kimberlites suffer pervasive post-magmatic alteration continuously monitored by UV DOAS spectrometers that makes them unsuitable for study of their volatile installed as part of the Network for Observation of Volcanic inventory. The Quaternary-aged kimberlites from the and Atmospheric Change (NOVAC) programme. The SO2 Igwisi Hills volcanoes, Tanzania (Brown et al. 2012), have emissions from the volcano have also been observed and avoided alteration and are amenable to detailed geochemical characterised by the satellite-based UV spectrometer OMI and isotopic investigation. (Ozone Monitoring Instrument). Tungurahua is therefore an The 3He/4He of melt trapped in olivine xenocrysts ideal location for comparing ground- and satellite-based estimates of volcanic SO2 emissions. Although OMI SO2 released by crushing in vacuo (4.1 ± 0.2 Ra; n = 4) are amongst the lowest recorded for mantle rocks. The data rule retrievals for continuous tropospheric degassing are not yet out a deep mantle plume source that has been implicated in validated, the dataset represents a large and mostly the origin of the Udachnaya (Sumino et al. 2006) and untapped resource for volcano monitoring, particularly in Tertiary West Greenland (Tachibani et al. 2006) remote or inaccessible regions. This novel study seeks to kimberlites. Importantly, the 3He/4He are significantly improve agreement between the DOAS and OMI datasets lower than of the value of regional sub-continental for Tungurahua, and gain new understanding of why lithosphere as measured in peridotite xenoliths from differences in the two estimates of SO2 degassing arise. Uncertainties affecting comparison between the datasets Lashaine, Eledoi and Pello Hill (6.3 - 7.3 Ra (Porcelli et al. 1986)). Phenocryst olivine δ18O (5.1 ± 0.2 ‰; n = 11) are include: the different natures of the quantities measured indistinguishable from normal mantle peridotite, with no (flux vs column concentration); the impact of local indication of derivation from an enriched mantle source atmospheric and meteorological conditions (e.g. clouds proposed for Udachnaya kimberlites (Kamenetsky et al. masking volcanic plumes; humidity and temperature 2008). promoting rapid loss of SO2 via oxidation to sulphate or by The simplest explanation for the isotope data is that the various wet/dry deposition processes; wind dispersal of Igwisi Hills kimberlite originates as volatile-rich small plumes); and differences in the spatial and temporal volume melts from normal sub-continental lithosphere resolution of measurements. mantle without the need for thermal perturbation originating We present a novel numerical modelling-based study of at depth. The low 3He/4He in the melt implies that the volcanic SO2 emissions from Tungurahua using the mantle is heterogenous for U and Th, with early melting atmospheric chemistry/transport model REMOTE, which phase preferentially enriched relative to bulk mantle values. has already been successfully applied to modelling post- emission SO2 dispersion from volcanoes in Nicaragua and Brown, R.W., Manya, S., Buisman, I., Fontana, G., Field, Indonesia. Model input is high time resolution SO2 flux data M., Mac Niocaill, C., Sparks, R.S.J. & Stuart, F.M. from the Tungurahua DOAS datasets. The model output is (2012) Bulletin of Volcanology. 74, 1621-1643. spatial maps of SO2 column concentration for comparison Sumino, H., Kaneoka, I., Matsufuji, K. & Sobolev, A.V. with those produced from OMI data. We calculate total (2006) Geophysical Research Letters 33, L16318. daily atmospheric SO2 burdens for the REMOTE and OMI Tachibani, Y., Kanoeka, I., Gaffney, A. & Upton, B. (2006) datasets, and use REMOTE’s treatment of atmospheric Geology 34, 273-276. chemical reactions, wind dispersal, and cloud cover, as well Porcelli, D.R., O’Nions, R.K. & O’Reilly, S.Y. (1986) as additional OMI data products (effective reflectivity and Chemical Geology 54, 237-249. aerosol index) and ground-based observatory records to Kamenetsky, V.S., Kamentsky, M.B., Sobolev, A.V., interpret the variation in agreement between the two Golovin, A.V., Demouchy, S., Faure, K., Sharygin, datasets. A key aim is to identify whether any of the above V.V.& Kuzmih, V.D. (2008) Journal of Petrology 49, sources of uncertainty are dominant, and to investigate 823-839. potential means of correcting for these. Additionally, we seek to produce a detailed assessment of errors in each dataset.

56 VMSG 2013 – Poster Presentation Abstracts

(Mis)understanding bubble growth Granitoid magmatism during in magma: Evidence from preserved continental rifting: Preliminary volatile concentration gradients in insights from the Oslo Rift, Norway

glass C. MCLEOD*1, A. BRANDON 1, R. TRØNNES2, T. LAPEN1 I.M. MCINTOSH*1, E.W. LLEWELLIN1, M.C.S. 1 University of Houston, Dept. Earth and Atmospheric HUMPHREYS, M.C.S.2, A. BURGISSER3, C.I. SCHIPPER3, Sciences, SR1, Houston, Texas, 77204-5007. A.R.L. NICHOLS4 (*[email protected]) 2 Natural History Museum, University of Oslo, Blinderm, 1 Department of Earth Sciences, Durham University, UK. 0318 Oslo, Norway. (*[email protected])

2 Department of Earth Sciences, University of Oxford, UK. The rifting of a continent is a crucial step in the Wilson 3 Institut des Sciences de la Terre d’Orleans, CNRS – cycle of supercontinent formation and breakup during l’Universite d’Orleans, France. which large scale changes are imposed on the architecture 4 Institute for Research on Earth Evolution, JAMSTEC, Japan. of the lithosphere. The Permo-Carboniferous Oslo Rift in

southern Norway is a failed intracontinental rift which Volcanic eruptions are driven by the nucleation and developed in the Precambrian continental Baltic Shield and growth of bubbles that form as volatiles (chiefly water) produced a large variety of alkaline volcanic and plutonic exsolve from magma. Bubbles grow as volatiles in the melt rock types. The current erosional level is up to 3 km below diffuse down a concentration gradient towards and across the original surface and has exposed the plutonic roots of the bubble wall; understanding how this gradient evolves the magmatic plumbing systems. Examination of the over time underpins numerical modelling of bubble growth granitoid roots within the rift provides the opportunity to 1) and is critical to understanding bubble growth mechanisms. evaluate contributions from mantle and crustal sources We present analytical results of water concentration during continental rifting 2) assess the importance of crustal gradients surrounding bubbles in experimentally recycling and 3) investigate the timing of granitoid decompressed volcanic glasses. These data highlight the petrogenesis so that temporal constraints on rift related hitherto unrecognised importance of hydration and bubble magmatism can be obtained. These fundamental questions resorption during quench, with implications for both regarding the evolution of a continental rift will be experimental and natural samples. Water speciation data addressed by a thorough microanalytical geochemical study suggest a mechanism for this quench hydration and of constituent minerals within the exposed plutonic roots. represent a potential approach for correctly interpreting the The granitic units of the Drammen and Finnemarka cause of hydration profiles observed in natural samples. intrusive complexes in the Central segment of the Oslo Rift Whereas bubble growth theory predicts decreasing have previously been studied for their whole rock volatile concentrations towards the bubble wall, our data 1 geochemical compositions (TrØnnes and Brandon, 1992) instead show increasing water concentrations, of up to and therefore form the basis of this work. Rock types 3wt%, in the ~30 microns closest to the bubble wall. Water include apilitic porphyry, quartz monzodiorite, rapakivi concentration at the bubble wall must always be the granite and oligioclase granite (which are not comagmatic). equilibrium solubility value for the given pressure and Sampled units are predominantly peraluminous (up to 1.2 temperature conditions. Observed hydration profiles result Al O /(CaO+Na O+K O) and exhibit marked differences in from the increase in equilibrium solubility value as 2 3 2 2 age corrected Sr-Nd-Pb isotopic compositions e.g the temperature decreases during the quench to glass, and Finnemarka exhibits εNd values of +3.5 to +4 where as the locally overprint the broader concentration gradient Drammen ranges from +1 to +1.5. In-situ U-Pb ages of resulting from syn-experimental bubble growth. Quench zircons from both intrusive complexes will constrain the resoprtion resulting from hydration may reduce bubble timing of magmatism in this segemnt of the rift and volumes and sample porosities by as much as a factor of identify the role (or not) of crustal recycling. Additional in- two. situ Hf and O isotopic and trace element analyses will Quench timescales are too rapid (1-5 seconds) for characterise the components of magma source reservoirs hydration profiles to be explained by diffusivity of ‘total’ and microdrilling of feldspars for their Sr-isotopic water (H O ). Speciation data showing molecular (H O ) 2 t 2 m compositions will asses the role of crystal recycling by and hydroxyl (OH) water concentrations around bubbles identifying the crystal cargoes of the different intrusive reveal that quench hydration is driven by rapid diffusion of units. H Om. Speciation data thus offer a methodology for 2 interpreting the pressure and/or temperature causes 1 Trønnes and Brandon (1992). Mildly peraluminous high responsible for hydration profiles surrounding bubbles in silica granites in a continental rift: the Drammen and natural samples. Finnemarka batholiths, Oslo Rift, Norway. Contributions to H O data are collected using the SIMS-calibrated 2 t Mineralogy and Petrology, v. 109, 275-294. backscatter SEM technique of Humphreys et al (2008) and are presented as 2D greyscale maps of H2Ot variations and as sample-averaged H2Ot profiles corresponding to different experimental conditions. H2O speciation data are collected using FTIR Stingray imaging and presented as 2D maps of

H2Ot, H2Om and H2Om/H2Ot ratios. Humphreys, M.C.S. et al (2008) EPSL 270, 25-40.

57 VMSG 2013 – Poster Presentation Abstracts

Norwegian larvikites: Colours & Exploring volcanic-plutonic origin: An oxygen isotope study connections

I.G. MEIGHAN *1,2,3,T. FALLICK 1, R. ELLAM1 V. MEMETI*1, J. DAVIDSON1 1 S.U.E.R.C., East Kilbride. (*[email protected]) 1 Durham University, Dept. of Earth Sciences, Science Site, 2 Geological Survey of N.Ireland, Belfast South Road, Durham, DH1 3LE. 3 Geology Department, Trinity College Dublin (*[email protected])

Larvikite, a coarse-grained olivine-augite syenite of the Understanding the geochemical connection of arc Permian Oslo Province and Norway’s National Rock,forms volcanic rocks with their underlying magma plumbing a large intrusive complex extending E and W of Larvik. system remains a great challenge in arc studies. Volcanic This comprises both nepheline- and quartz-bearing varieties and plutonic rocks are often studied separately, but rarely whose colours are light grey(predominant),black or red. together as an interconnected plumbing system, which has This variation in itself invites O isotopic investigation. often led to inconsistent interpretations in the past. The The larvikites of this main body are cumulates with challenge is that, in many cases, either the volcanoes are virtually omnipresent igneous lamination (inwardly inclined accessible with their subjacent plumbing system buried, or at 450-900). Their emplacement involved multi-injection by the plutons are exposed with their superjacent plumbing magmatic pulses, each probably coinciding with eruption system eroded. from an overlying (now eroded) Kilimanjaro-type central The incentives for studying the entire magma plumbing volcano. Such an ‘open system’model accounts for a lack of system of a volcanic-plutonic complex are 1) to examine if major cryptic layering. we can associate certain volcanic rocks with specific 8 samples (7feldspars, 1whole rock) define a relatively plutonic units and if they are equivalent to one another, narrow delta 18O range of +5.9 to +7.2 per mil (VSMOW: complementary, or not related in their geochemical analytical precision +/- 0.2, 1 sigma). Our conclusions are: characteristics; 2) to determine if we can pinpoint evidence 1. There is no obvious difference between light and dark in the geochemical record of both rock types which larvikite (these can be interlayered) magmatic process(es) caused the large ignimbrite eruptions 2. The only significant variation involves the reddened, compared to the smaller sized volcanic eruptions, 3) to quartz larvikite whose feldspar (6.7)and whole rock(7.2) examine the length and time scales of such processes, and if are elevated relative to the other feldspar values(5.9- mixing drives eruptions - as is often suggested – then 6.2). Thus the reddening cannot be attributed to high T, determine where mixing occurred (magma reservoir or subsolidus meteoric water-rock interaction and probably conduit), and 4) to try to reconcile the often disparate time involved magmatic fluid scales and durations of magma processes inferred from both 3. Excluding the reddened material,the larvikite feldspars rock types. have values close to +6 per mil. Accepting these We have collected samples from two calderas in the approximate magma compositions, the data support USA, where contemporaneous volcanic and plutonic rocks gravity and other isotopic evidence indicating syenite of the same arc magma plumbing system are juxtaposed, genesis by deep crustal/ Upper Mantle fractional allowing the examination of the physical and geochemical crystallisation of alkali olivine basalt magma. connections between the two realms and the overall evolution of each magma plumbing system through time. One is the 33 Ma Bonanza caldera of the central San Juan Volcanic Field in Colorado and the other is the 36-34 Ma Organ Mountains caldera in New Mexico. Both calderas have been tilted on their sides due to extensional tectonics along the Rio Grande Rift. The compositional changes in these calderas are fairly similar in that they are composed of crystal-rich to crystal-poor dacites, often crystal-poor rhyolite, and minor andesite flows and intrusions. The plutonic rocks range from medium to fine grained diorites to leucogranites and cluster around granodioritic compositions. And most importantly, both systems were magmatically active for only 1-2 myr according to new Sanidine 40Ar/39Ar geochronology (pers. comm. M. Zimmerer, New Mexico Bureau of Geology and Mineral Resources). We have looked at the structural relationships in the field and are in the initial stages of establishing geochemical characteristics of these rocks using whole rock and single mineral element and isotope geochemistry. We will present some of our initial results from whole rock element geochemistry and cathodoluminescence imaging of minerals from volcanic and plutonic rocks of both calderas to start address some of the questions outlined above.

58 VMSG 2013 – Poster Presentation Abstracts

Magma storage and differentiation Constraining the pre-eruptive beneath Dabbahu Volcano, Afar, storage conditions for the Pollara Ethiopia eruptions of Salina, Italy

H. MILROY*1 H. MORETTI*1, J. GOTTSMANN1, R. SULPIZIO2, J. BLUNDY1 1 School of Earth Sciences, University of Bristol. (*[email protected]) 1 Department of Earth Sciences, Bristol University, Wills Memorial Building, Queens Road, Bristol. BS8 iRJ. Erupted rock types from Dabbahu Volcano, Afar, (*[email protected]) Ethiopia have been interpreted as a full fractional 2 Dipartimento di Scienze della Terra e Geoambientali, crystallisation suite from a single parent basalt. Petrological Universitá di Bari, via Orabona 4, 70125, Bari, Italy. analysis and 40Ar/39Ar dating show no systematic temporal evolution of erupted products. Evidence from InSAR and Salina is the second largest of the Aeolian Islands that seismic data and melt inclusions suggest shallow magma form a complex of faults and volcanic arcs to the north of storage, while magnetotellurics has imaged substantial Sicily, Italy. The explosive eruptions of the Pollara volumes of melt in the upper and lower crust beneath depression, 26.5-13.6 ka, are believed to be the result of the Dabbahu. invasion and chaotic mixing of a shallow, partially We present results from a two-dimensional numerical fractionated, basaltic-andesite by a highly evolved rhyolite. modelling exercise, which tested the hypothesis that the The invasion by a more evolved magma is unusual and is extreme diversity of compositions found at Dabbahu can be supported by the stratigraphy of the air fall deposits. The differentiated and stored at shallow crustal levels by the volatile content of each body has been calculated by episodic injection of basaltic dykes, at intervals consistent working back from an assumed value for the mafic body, with the known rift spreading rate and the minimum age of requiring a high volatile input from the silicic magma (4-4.5 Dabbahu. wt %). The full range of compositions observed at Dabbahu The depths of the magma bodies are assumed to be in was reproduced by the modelled system, and stored line with those found generally in the Aeolian arc. This simultaneously at shallow crustal levels. Results suggest presents a paradox where the more evolved melt is deeper that the system may have been evolving for ~300 kyr. (200-300 MPa) than the juvenile mafic melt it later invades Estimates of the modelled conductivities are compared with (100-200 MPa). the amounts of melt beneath Dabbahu, estimated by MT This study will use the volatile content of the numerous imaging studies. trapped melt inclusions to constrain the storage depths and ascent history of each magma body and any deeper parent that may be feeding the shallower chambers. Isotope anlaysis will examine the degree of crustal contamination and the melt history will be experimenatlly reconstructed. Microprobe analysis of the rims of large ubiquitous plagioclase phenocrysts will be used to determine the speed of mixing by constraining the rate of chemical diffusion in banded and streaky pumices.

59 VMSG 2013 – Poster Presentation Abstracts

Making granites in the BPIP: How Degassing of sulphur from did the evolved rocks in Centre 3, sediments in the Siberian Traps Ardnamurchan form? Large Igneous Province

J. MURRAY*1, F.C. MEADE2, R.M. ELLAM3, V.R. S. NOVIKOVA1*, C. YALLUP1, M. EDMONDS1, TROLL2 A.V.TURCHYN1, J. MACLENNAN1, H. SVENSEN2 1 School of Geography, Earth and Environmental Sciences, 1 Earth Sciences Department, University of Cambridge, University of Birmingham, UK. Downing Site, Cambridge CB2 3EQ, UK. (*[email protected]) (*[email protected]) 2 Department of Earth Sciences, Uppsala University, 2 Dept. of Physics, PO box 1048 Blindern, 0316 Oslo, Sweden. Norway 3 Scottish Universities Environmental Research Centre, UK. The eruption of the Siberian Traps igneous province, at The Ardnamurchan Central Complex is part of the the Permo-Triassic boundary, was synchronous with the British Palaeogene Igneous Province (BPIP) and formed in largest mass extinction in the geological record. The response to the opening of the North Atlantic Ocean. eruptions likely caused a climatic perturbation, although Ardnamurchan lies within the Northern Highlands Terrane, there is uncertainty regarding its magnitude, as it is unlikely the basement of which is composed of Lewisian granulite that the magma itself could contain enough volatiles to have and amphibolite facies gneiss, overthrust by psammites of as dramatic an environmental impact as observed. The the Moine Supergroup. These basement country rocks are missing component might be the degassing of the country overlain by Jurassic shale, mudstone and limestone. Centre rocks (oil shales and evaporites) during heating by sill 3, the youngest of the centres in Ardnamurchan, is intrusion [1]. It has been hypothesized that the fluxes of dominated by the Great Eucrite, a gabbro lopolith, with a carbon gases derived during contact metamorphism of small proportion of tonalite and quartz monzonite in the sedimentary rocks and intruded LIPs may be sufficient to centre. cause climate change of the right order of magnitude [1]. Using whole rock Sr and Pb isotope ratios, major, trace Furthermore, gas-venting structures (filled with magmatic- and rare earth element (REE) geochemistry, we aimed to sedimentary breccias) have been described in the Lower settle the long-standing debate over the exact mechanisms Tunguska region of the Siberian Traps, which might by which these evolved rocks formed. Richey & Thomas represent pathways through which the gas escaped to the (1930) proposed a separate stock shaped intrusion, which surface [1]. While there has been much work done in cross cuts the earlier gabbros. Other studies (e.g. O’Driscoll, quantifying the potential carbon yield from the 2007) have suggested that Jurassic sedimentary rocks may devolatilisation of sediments, there has been no attempt to have melted and pooled above the centre of the gabbro quantify the potential sulphur yield, despite this being lopolith, mixing and forming tonalite and quartz monzonite; perhaps the most important species for dramatic short-term however a full geochemical study has not been previously climate change. We present bulk rock sulphur and carbon undertaken. concentrations, monosulphide, bisulphide and sulphate Rare earth element data shows significant LREE concentrations and sulphur isotopic compositions, for both enrichment, indicating a strong crustal component to the igneous (sill, lava flow, tephra) and sediments (shale, magma, but does not differentiate between the similar evaporates) for the Nepa and Norilsk regions of the Siberian Moine and Jurassic REE signatures. However, the evolved Traps. We also present homogenised olivine-hosted melt rocks also have a very strong Lewisian granulite-facies Pb inclusion major, trace and volatile data for the lavas. We and Sr isotope signature, which indicates that the magma show that there is evidence for sulphur assimilation from has assimilated large volumes of Lewisian granulite-facies volatile-rich country rocks, consistent with work done on gneiss, deep in the lower crust. Therefore, a Moine mineralised intrusions in the Norilsk region [2]. We influence on the REEs is most likely as the Jurassic rocks consider the implications of the data for the total volatile are structurally above the gabbro. budget of the eruptions. Our findings disprove the theory that the evolved rocks of Centre 3 are a cap, formed by in-situ melting and mixing [1] Svensen, H., Planke, S., Polozov, A. G., Schmidbauer, on top of the gabbro lopolith. Instead their formation has N., Corfu, F., Podladchikov, Y. Y., Jamtveit, B., (2009) been much more complex. We show that these evolved Earth and Planetary Science Letters 277, 490–500. magmas formed by AFC processes, with assimilation of [2] Li, C., Ripley E. M., Naldrett, A., Schmitt, A., Moore, Lewisian granulite-facies basement taking place in the C. (2009) Geology 37, 259-262 lower crust. This was followed by assimilation of Moine country rock within the upper crust, with eventual intrusion as a central stock, as originally suggested by Richey & Thomas (1930).

Richey, J, E. & Thomas, H. H. (1930) The Geology of Ardnamurchan, North West Mull and Coll. Memoir of the Geological Survey of Great Britain (Scotland), 393pp. O’Driscoll, B. (2007) Geol Mag 144 897-908.

60 VMSG 2013 – Poster Presentation Abstracts

The post-Minoan plumbing system Geochemical evidence for relict behaviour at Santorini Volcanic degassing pathways in andesite

field: Implications for the current M. PLAIL*1, M. EDMONDS2, M.C.S. HUMPHREYS3, J. unrest phase BARCLAY1, R. HERD1 1 School of Environmental Sciences, University of East C.M. PETRONE*1, L. FRANCALANCI2, G.E. Anglia, Norwich Research Park, Norwich, NR4 7TJ, VOUGIOUKALAKIS3 UK (*[email protected]) 1 Natural History Museum, Dept Earth Sciences, Cromwell 2 Department of Earth Sciences, University of Cambridge, Road, SW7 5BD London (*[email protected]) Downing Street, Cambridge, CB2 3EQ, UK 2 Dipt Scienze Terra, Universita’ di Firenze, Firenze-Italy. 3 Department of Earth Sciences, University of Oxford, 3I.G.M.E., 3rd Entrance Olympic Village, Athens-Greece. South Parks Road, Oxford, OX1 3AN, UK

The post-caldera islets of Palea- and Nea-Kameni The andesitic Soufrière Hills Volcano (SHV), active formed as result of nine eruptive events from 197 B.C till since 1995, emits large fluxes of volcanic gases, even 1950 A.D. in the center of the Santorini Minoan caldera. during eruptive pauses lasting > 1 year. It has been observed These nine eruptive events led to the emplacement of that the flux of gas is largely decoupled from the flux of dacitic lava flows and domes also characterised by the magma to the surface, indicating efficient magma-vapour presence of basalts to andesites magmatic enclaves. Dacitic segregation, followed by vapour transport to the surface. rocks have low porphyritic index, which increases with Evidence for vapour transport through magma is not often time. Plagioclase is the prevalent mineral phase, followed preserved in the erupted rocks, perhaps due to overprinting by clinopyroxene, orthopyroxene, opaque minerals and during eruption, or because the transport zones themselves apatite. Few resorbed xenocrysts of olivine with coronae of are not usually erupted. pyroxene are also present. Basaltic to andesitic mafic Andesite blocks in deposits from two recent eruptive enclaves have variable texture spanning the entire range events from SHV contain narrow shear zones, up to 2 m in from cumulate to aphyric. In some eruptive events, length and 2-10 cm in width, with alternating darker fine- porphyritic enclaves with olivine in groundmass are also grained and lighter coarser-grained bands. Analysis has found. Host lavas show a general decrease of the evolution shown that the dark, fine-grained bands (grain size ~30-70 degree with time, at the same time Mg# of pyroxenes and µm) have very low vesicularity (~1%) with abundant zones anorthite contents of plagioclase decrease from mafic of oxides (<8% vol), cordierite, groundmass cristobalite and enclaves to host lavas. Mafic enclaves have major and trace resorbed plagioclase. The light, coarse bands (grain size element compositions falling on the low-silica prolongation ~100-350 µm) consist of broken plagioclase, of host lavas compositional trends. Sr isotopes orthopyroxene, clinopyroxene and sparse large amphibole systematically increase with time and thus toward the less crystals. Vesicularity ranges from 7 to 19 vol% with evolved compositions of lavas and mafic enclaves. The reduced abundance of oxides (<2.4% vol) relative to the latter, along with mineral separates, generally show slightly darker non-vesicular bands. Glass is rare to absent in both more enriched radiogenic compositions in respect with host types of band. Mineral compositions in the shear zones are lavas, with the exception of the 46-47 A.D. products. All identical to the established mineral compositions in the data point to mixing/mingling processes between mafic and andesite at SHV. However, bulk XRF analyses indicate that dacitic magmas. Our data suggest the existence of a shallow some metal concentrations are greatly enhanced relative to layered reservoir where mixing/mingling processes take the surrounding andesite. For example, copper place at the interface between the upper dacitic magmas and concentrations are up to four times higher than the andesite the lower mafic magmas. Cumulus processes, crystal host. Copper is typically present as copper sulphide fractionation eventually accompanied by variable degree of inclusions in Ti-magnetites and plagioclase phenocrysts. crustal assimilation, also characterised the lower part of the We hypothesise that the elevated metal concentrations plumbing system allowing further layering and evolutionary and presence of abundant, disseminated metal-bearing processes of the mafic magmas which, in turn, generate the grains are evidence that these zones are relic vapour complex and variable textures shown by mafic enclaves. transport pathways in the shallow volcanic system. Rapid Different parts of the layered reservoir were frequently and shear of andesitic material formed brittle fractures either at variably sampled during time, pointing to multiple arrivals the conduit wall or in the shallow dome, along which metal- of mafic magmas during the post-Minoan activity of bearing vapour or fluid was transported. During shearing, Santorini suggesting a still very active magma source in frictional heating caused both partial melting, and volatile good agreement with the current unrest phase at Santorini resorption. These sheared zones may provide the first Volcanic field. petrological evidence for vapour transport at SHV, and a window onto the early stages of mineralization at island arc volcanoes.

61 VMSG 2013 – Poster Presentation Abstracts

Textural variations of groundmass Reconciling sulphur dioxide microlites in the 2006 and 2010 emissions from satellite data with eruptive products of Merapi petrological volatile data for volcano, Indonesia: Evidence for explosive eruptions of Mount Etna, magma ascent and shallow conduit Italy

processes L. SALEM*1, M. EDMONDS1, B. MCCORMICK1, S. 2 *1 1 2 1 CARN K. PREECE , J. BARCLAY , R. GERTISSER , R. HERD 1 1School of Environmental Sciences, University of East Department of Earth Sciences, Downing Street, University Anglia, Norwich, NR4 7TJ, UK. of Cambridge, Cambridge CB2 3EQ, United Kingdom (*[email protected]) (*correspondence: [email protected]) 2 2School of Physical and Geographical Sciences, Keele Department of Geological and Mining Engineering and University, Keele, Staffordshire, ST5 5BG, UK. Sciences, Michigan Technological University, Houghton, MI, USA Feldspar microlite textures in scoriaceous and dense block-and-ash flow (BAF) samples from the 2006 eruption The rise of new satellite-based instruments such as the of Merapi elucidate short timescale variations of shallow Ozone Monitoring Instrument (OMI) grant the opportunity magmatic processes during a typical dome-forming Merapi to measure SO2 released during volcanic eruptions with eruption that can be compared to microlite textures in the greater sensitivity than ever before [1]. Satellites remain the rapidly extruded lava dome during the cataclysmic eruption safest and most effective method of assessing eruptive SO2 mass. We present a new OMI dataset of SO2 emissions from in 2010. Measurements of areal number density (NA), mean microlite size, crystal aspect ratio and groundmass the eruptions of Mount Etna, Italy, between October 2004 crystallinity (φ), combined with the monitoring record and and December 2008. Known uncertainties in the OMI field observations, allow interpretation of magma ascent dataset such as interference from cloud cover, seasonal and processes. Crystal size distribution analysis provides altitudinal variations in detection limit, and variable spatial constraints on the timing of crystallisation and identifies resolution are quantified. OMI data are compared to other that both growth- and nucleation-dominated crystallisation satellite and ground-based observations of these eruptions. regimes existed during the 2006 eruption, resulting from The SO2 output during an eruption is dependent on the changing conditions of undercooling (ΔT) during variable pre-eruptive concentrations of sulphur in the melt and in the magma ascent paths. Stage I of the 2006 eruption (BAFs vapour, and on the erupted mass of lava. It has been emplaced between 11th May and 1st June 2006) was observed that a large fraction of sulphur exsolves into characterised by variable magma ascent and extrusion vapour prior to eruption for oxidized magmas [2]. A direct rates, with calculated crystallisation time scales correlating comparison between gas emissions data and petrological with the monitoring record of magma moving at shallow data, combined with data on erupted volumes, will allow depths within the edifice. Stage II samples (BAFs emplaced assessment of the gas/melt ratio for different eruptions, and on 14th June 2006) provide evidence of more rapid magma for different stages within an eruption, which might be ascent, over a period of a few days, from depths within the related to eruption style. The formation of a gas-rich “cap” amphibole stability field. Stages III (post 14th June BAFs) in the magma reservoir prior to eruption, for example, might and IV (remnants of 2006 dome at the summit) indicate that lead to high gas emissions relative to erupted magma later magma batches stalled temporarily at shallower levels volumes at the beginning of an explosive eruption. (< ~ 3 km) before being extruded, supporting a previously Literature will be mined for measurements of sulphur in proposed idea of a shallow, ephemeral magma chamber at olivine-hosted melt inclusions for explosive eruptions Merapi. Despite basaltic andesite whole rock compositions, between 2004-2008. The inclusion data will be compared to groundmass glass is rhyodacitic to rhyolitic, with the the OMI time series to generate an empirical model for compositional variation correlating with groundmass sulphur partitioning between melt and vapour. We will use crystallinity. Plagioclase microlite compositions show the model to predict the SO2 output for a large historical evidence of decompression-induced degassing, often eruption of Mount Etna for which no satellite data is displaying more alkali-rich (anorthoclase) rims. In contrast, available. To this end, we have analysed olivine-hosted melt analysis of the fast-growing 2010 lava dome preserves inclusions for major and volatile species in tephra erupted evidence of a crystallisation regime more strongly during the 1669 Monti Rossi flank eruption, which was the dominated by nucleation, due to higher ΔT during faster largest eruption in the last four hundred years at Mount ascent. Etna. This work shows that even during an effusive (VEI 1) dome-forming eruption at Merapi, such as in 2006, magma [1] McCormick, B.T., et al. 2012. Remote Sensing of ascends quickly from depth, over a period of a few days. Volcanoes and Volcanic Processes: Integrating Such behaviour offers little warning time to evacuate the Observation and Modelling. In press. Geological surrounding densely-populated region, inhabited by over 1 Society of London Special Publication million people. During 2010, higher ascent rates, inhibiting [2] Wallace, P.J., M. Edmonds, 2011. The Sulfur Budget in magma degassing and causing increasing overpressure, are Magmas: Evidence from Melt Inclusions, Submarine interpreted to have contributed to the increased explosivity Glasses, and Volcanic Gas Emissions. Reviews in compared to 2006. Mineralogy and Geochemistry 73 (1) pp.215-246

62 VMSG 2013 – Poster Presentation Abstracts

Effects of Shear Strain on Effect of f O2 on phase relations and Deformation and Degassing of sulphur mobility during magmatic Three-Phase Magmas differentiation of a basaltic andesite

J. SHIELDS*1, L. CARICCHI2 , D. FLOESS3, H. MADER1, S. SKORA*1, J. BLUNDY1 M. PISTONE4 1 School of Earth Sciences, University of Bristol, Wills 1 School of Earth Science, University of Bristol, Bristol, UK Memorial Building, Bristol, BS8 1RJ, UK. (*[email protected]). (*[email protected]) 2 University of Geneva, Geneva, Switzerland. 3 University of Lausanne, Lausanne, Switzerland. New geochemical data suggest that parental magmas 4 Geochemistry and Petrology, ETH Zurich, Switzerland generated in subduction zones have similar base and precious metal concentrations compared to that of mid Simple-shear experiments were performed on synthetic, ocean ridges (1,2). Hence, enrichment of these metals that haplogranitic magmas, with 12-36 initial vol.% CO2-rich ultimately lead to the formation of large porphyry copper bubbles and 0-42 initial vol.% crystals, in a HT-HP deposits must be explored in the light of magmatic Paterson-type pressure vessel, to final strains between γ=0 differentiation processes beneath arcs. A very important and γ=10. 3-D imaging and analysis of microstructures was parameter to consider is thereby fO2 because of the performed using x-ray tomography and Blob 3D software. chalcophile nature of Cu (and many other base and precious Bubble elongation and coalescence begins as low as γ=0.3 metals), coupled to the redox sensitive mobility of sulphur

(φb 20 vol.%) and increases with deformation to produce (simplified speaking, sulphur is mobile as sulphate under planar bubble networks at γ=5 (φb 16 vol.%). Bubble oxidising conditions, whereas it is immobile as sulphide connectivity, localization of strain and brittle fracturing of under reducing conditions). It is further suggested that samples increase with crystal content. Progressively lower magmatic crystallization under oxidising conditions bubble volume percentages with increasing strain, along (keeping sulphides such as pyrite absent, which would with strain-hardening rheological behaviour, suggest scavenge Cu) is key in pre-enriching Cu to economically significant shear-induced outgassing, which likely occurs valuable concentrations (1). through the development of connected bubble or fracture We have conducted a preliminary set of fO2-buffered, S- networks. Evidence for formation and subsequent closure doped piston cylinder experiments (5 kbar, 950-1150°C; fO2 of permeable pathways provides an effective mechanism for = QFM-1.5 and + 0.5; QFM = quartz-fayalite-magnetite considerable degassing of samples, which are analogous to buffer), exploring the phase relations of a basaltic andesite volcanic conduits at depth. This could explain the observed that is representing the most mafic compositions erupted by transitions from explosive to effusive activity observed at Lascar Volcano (Andes, Chile) (3). The liquidus is located at many silicic volcanoes, as well as the formation of flow- 1100°C > T > 1150°C. Phases to appear with decreasing banded obsidian. temperature are: spinel ± FeTi oxides, followed by orthopyroxene, clinopyroxene & plagioclase. In agreement with previous studies, we find that e.g. phase relations and

crystallinities at constant temperatures vary with fO2, (with run products being considerably more crystalline under oxidising conditions). Anhydrite (a sulphate) is the sulphur bearing phase in oxidising experiments, appearing in run products at T ≤ 1050°C. Sulphur phase-in under reducing conditions was not yet found, likely owing to the high melt fraction in these experiments, even at low temperatures (950°C). We speculate that a sulphide will be the sulphur- bearing phase that joins the assemblage at lower temperatures. Anhydrite, in contrast to e.g. pyrite, is not known to be a good host for Cu. Our preliminary results hence suggest that oxidising conditions inhibit the formation of a sulphide phase, keeping sulphur (and by inference Cu) mobile. In contrast to other studies, we find that sulphate is stable over sulphide at QFM+ 0.5, which is about 1 log unit lower than previously reported. This discrepancy is likely explained by the highly complex behaviour of sulphur as a function of

fO2, Fe concentration, Fe/S, melt polymerization, X(H2O), etc. Future experiments will continue to explore phase relations and sulphur solubility and speciation in crystallizing, mafic magmas.

[1] Jenner, F.E. et al. (2010) J. Petrol. 51, 2445-2464. [2] Lee, C.-T. et al. (2012) Science 336, 64-68. [3] Matthews, S.J. et al. (1999) J. Petrol. 40, 1891-1919.

63 VMSG 2013 – Poster Presentation Abstracts

Timescales of upper crustal Triggering of major volcanic residence at Campi Flegrei, Italy eruptions recorded by actively

V.C. SMITH*1, K. SAUNDERS2, R. ISAIA3 forming cumulates on Tenerife 1 University of Oxford, Research Laboratory for M.J. STOCK*1,2, R.N. TAYLOR2, T.M. GERNON2 Archaeology and the History of Art, Dyson Perrins 1 Department of Earth Sciences, University of Oxford, OX1 Bldg, Souths Parks Rd, Oxford OX4 1SA 3AN (*[email protected]) (*[email protected]) 2 School of Ocean and Earth Science, University of 2 University fo Bristol, Department of Earth Sciences, Wills Southampton, SO14 3ZH Memorial Building, Queens Rd, Bristol BS8 1RJ

3 Istituto Nazionale di Geofisica e Vulcanologia, Volcanic eruptions are commonly triggered by the Osservatorio Vesuviano, via Diocleziano 328, 80154 interaction between two compositionally discrete magma Napoli, Italy batches1. This may occur within either an open or closed

system and within numerous geologic environments. Campi Flegrei caldera, Italy has produced some of the However, until now identification of pre-eruptive mixing largest eruptions in Europe, and has been very active in the events has been difficult in explosive systems, limited last 15 kyrs with more than 60 explosive eruptions. largely to interpretations based on whole rock analysis. We Zoned clinopyroxene crystals within these eruption have recovered partially developed (‘live’) cumulate mush deposits the provide a detailed record of the magmatic from the pyroclastic deposits of a series of major eruptions processes. Here we present compositional data, and use on Tenerife2. These samples represent frozen pieces of the diffusion chronometry to assess timescales of actively crystallising magma chamber, which are permiated crystallisation. These data provide information on range of with the final melt immediatley prior to each catastrophic melts generated beneath Campi Flegrei, magma flux rates, eruption. Through petrologic and geochemical analyses we and timescales of upper crustal storage. It is clear that have used these cumulate nodules as tools for examining magmatic system is open and that upper crustal residence is magmatic evolution prior to large-scale explosive volcanic short. There is also a clear relationship between vent eruptions on Tenerife. location, residence time and compositional evolution. Cumulate material recovered in each eruption is Changes in the composition of fumarole fluids, petrologically diverse. The most mafic nodules are wherlites seismicity, and deformation over the last 20 years indicates and pyroxenites, which are taken to represent material that that pulses of melt are periodically emplaced in the upper originated close to the chamber floor. Compositions range crust (Chiodini et al., 2012). This data is consistent with our through pyroxene hornblendite, horneblende gabbro, gabbro data that shows that the recent eruptions have tapped and syenite, with more evolved samples sourced from numerous pods of melt that were intuded into the crust progressivley higher layers. The variety of nodules within between 1 and ~70 years before the eruption. each deposit indicates that the magma resevoir completely

disintigrated on eruption, causing the well-documented Chiodini, G., et al. (2012) Geology 40, 943-946. caldera collapse events and ocean-island landslides2.

Major- and trace-element zoning profiles across cumulus plagioclase and clinopyroxene crystals record prolonged magmatic evolution through fractional crystallisation, punctuated by periodic mafic recharge events. However, the most striking feature of these zoning profiles is the consistant presence of a chemically distinct zone at the rim of cumulus crystals, which likely grew less than 1 yr before eruption. These mineral zones record the presence of a significantly more evolved melt throughout the cumulate pile. Pre-eruptive mixing with a felsic melt is confirmed through comparison between the REE composition of the intercumulus material and the modelled cumulus clinopyroxene-forming liquids. These felsic-mafic interactions are likely caused by destabilisation and overturn of the stratified magma chamber and represent a potential repeating trigger for large-scale plinian eruptions on Tenerife. This finding is important for hazard assessment on a populated island with on-going felsic volcanic activity.

[1] Sparks S. R. J. et al., 1977, Nature, 267, 315-318 [2] Brown et al., 2003, Geological Magazine, 140, 264-288

64 VMSG 2013 – Poster Presentation Abstracts

The Alpehué eruption, Sollipulli Evidence for an open magma Caldera, Southern Chile system feeding the compositionally

K. STREHLOW*1, A. FREUNDT2, S. KUTTEROLF2, J.C. diverse Laacher See (Germany) SCHINDLBECK2 eruption 1 Department of Earth Sciences, University of Bristol. E. TOMLINSON*1,2, V. SMITH3, M. MENZIES 2 (*[email protected]) 2 GEOMAR Helmholtz Centre for Ocean Research Kiel. 1 Department of Geology, Trinity College Dublin, Dublin 2, Ireland (*[email protected]) The ice-filled Sollipulli Caldera is located in the 2 Department of Earth Sciences, Royal Holloway University Southern Volcanic Zone of the Andean Volcanic Arc, of London, Egham, Surrey, TW20 0EX, UK. where subduction of the Nazca Plate induces volcanism. 3 RLAHA, University of Oxford, Oxford, OX1 3OY, UK. 2900 years ago, the plinian Alpehué eruption, originating from a vent at the caldera margin, emplaced pyroclastic The 12,9 ka eruption of the Laacher See volcano (East flow deposits and more than 14 km³ of fallout tephra from Eifel, Germany) represents one of the most violent recent eruption columns 16 to 28 km high with mass flow rates up eruptions in Europe. Approximaltely 6.3 km3 DRE (Harms to 3*107 kg/s. In order to better understand triggering and and Schmincke, 2010) of volatile rich phonolite magma dynamics of this event as a case study for future activity in erupted from what has previously been interprered as a this developing tourist region, we apply stratigraphic, continuously zoned magma chamber (Worner and granulometric, petrologic and geochemical methods to Schmincke, 1984a). constrain the magmatic evolution and the eruption history of Here, we present new major and trace element data for the Alpehué Tephra. volcanic glass and clinopyroxene from the Lower, Middle The fallout succession is stratigraphically divided by and Upper Laacher See Tephra (LLST, MLST and ULST). two prominent ash layers and several lithic-enriched layers, The data challenges the view that the LLST, MLST and and has a variable amount of crystal-ash matrix causing a ULST are directly related by fractional crystallisation (Tait bimodal grain size distribution. The eastward dispersal fan et al., 1989; Worner and Schmincke, 1984b). There is an is bilobate and asymmetric in shape as well as in lateral abrupt compostional gap between glasses of the MLST and grain-size and component distributions. We attribute these ULST, and ULST glass compositions indicate mixing with lateral variations to an atmosphere profile with a a more mafic composition. Co-erupted scoria (not tropospheric northwest wind and a stratospheric southwest previously reported) is found throughout the LLST and wind such that the longer their fall times the more are MLST. The scoria is basanitic and its trace element falling particles deflected southeastward. In addition, composition is consistent with the ULST mixing end- interaction with the glacier seems to have variably member. In addition, mingling between ULST and basanite phreatomagmatically influenced the eruption such that is seen at the top if the ULST unit, implying a second input subsequent eruption pulses reached different heights in the of basanitic magma into the Laacher See chamber. This is atmosphere. consistent with compositions of pseudo-oscillatory sanidine Juvenile components include the vastly dominant, pale- phenocrysts in th ULST, which imply significant beige trachytic to rhyolitic pumice, gray and banded temperature oscillations (Ginibre et al., 2004) pumices, very crystal-rich pumices resembling cumulates, This picture of varying melt composition (and and mafic lava nodules, which all together form well- temperature) at Laacher See is consistent with the emerging constrained differentiation trends from basalt to rhyolite that view that magma systems show temporal variability in are compatible with fractional crystallization of the temperature, crystallinity and melt composition and also in phenocryst phases. The cauliflower-shaped lava nodules the gradients of these variables, as well as being subject to represent mafic replenishing melt that was quenched against extensive open system processes (Bachmann and Bergantz, the colder trachyte/rhyolite magma. From mafic lava 2008). nodules to cumulate-like clasts of intermediate bulk-rock composition through to the most evolved rhyolitic pumice, Harms, E. and Schmincke, H.U., (2010) Contrib. Mineral. all share the same rhyolitic matrix-glass composition Petr. 138, 84-98. meaning that variations in bulk-rock compositions merely Worner, G. and Schmincke, H.U. (1984a) J. Petrol. 25, results from the variable crystal contents. Crystal re- 805-835. distribution in rhyolitic melt thus was the major cause of Tait, S.R., Wörner, G., Van Den Bogaard, P. and compositional zonation in the Alpehué magma chamber, Schmincke, H.-U. (1989) J. Volcanol. Geoth. Res. 37, which resided at 4-11 km depth in the crust as deduced from 21-37. cpx-liq barometry. With H2O contents of 4-6 wt% Worner, G. and Schmincke, H.U. (1984b) J. Petrol. 25, determined from plag-melt equilibria, the rhyolitic melt was 836-851. water-saturated at these depths. We thus conclude that the Ginibre, C., Worner, G. and Kronz, A. (2004) J. Petrol. 45, Alpehué magma was ready to erupt and that minor mafic 2197-2223. replenishment just served as the last straw to break the Bachmann, O. and Bergantz, G.W.. (2008) Rev. Mineral. camel's back. geochem. 69, 651-674.

65 VMSG 2013 – Poster Presentation Abstracts

What lies beneath? A Sr and Pb Degassing of sulphur from shale isotope study of intrusive rocks on adjacent to a dolerite sill in Skye: the Isle of Mull implications for the volatile budget

M. TURNBULL*1, F.C. MEADE2, G.R. NICOLL3, of large igneous provinces R.M. ELLAM4, V.R. TROLL2 C. YALLUP1, M. EDMONDS*1, A.V.TURCHYN1 1 Midland Valley Exploration, Glasgow, G2 2HG, UK 1Earth Sciences Department, University of Cambridge, (*[email protected]) Downing Site, Cambridge CB2 3EQ, UK. 2 Department of Earth Sciences, Uppsala University, SE- (*[email protected]) 753 36, Uppsala, Sweden 3 Neftex, Abingdon, Oxfordshire, OX14 4RY, UK We demonstrate, from a detailed outcrop-scale study, 4 Scottish Universities Environmental Research Centre, East that the mass of sulphur liberated from sediments during Kilbride, G75 0QF, UK contact metamorphism around a sill intrusion is similar to the mass of sulphur dissolved in the magma. This finding The Isle of Mull underwent extensive periods of volcanic and suggests the contribution of sulphur from sediment intrusive activity 60-55 Ma, forming 3 intrusive centres. Mull lies degassing might be just as significant as magmatic within the Northern Highlands Terrane, but is in close proximity to degassing during the emplacement of LIPs. We show that two major terrane boundaries, the Moine Thrust and the Great Glen sulphur and carbon have been devolatilised from shales Fault. Using detailed whole-rock geochemistry (major, trace and rare immediately surrounding a 3-metre thick dolerite sill in earth elements, Sr and Pb isotopes) the effect of crustal contamination Elgol, Skye, Scotland. Localised partial melting occurred on the intrusive rocks has been investigated and a prominent lack of within a few cm of the contact in the shale, generating melt- Pb isotope data, particularly for Centres 1 and 2 has been remedied. filled cracks. Sedimentary pyrite decomposed on heating The gabbros analysed appear to correlate with two distinct within 80 cm of the contact, generating sulphur-rich gases magma sources representing the REE compositions of the Mull lava (a mixture of H2S and SO2) and pyrrhotite. The remaining fields (Kerr et al. 1999). Centre 1 gabbros show a trend similar to the pyrrhotite was progressively enriched in 32S, due to the 34 Central Mull Tholeiites whereas Centre 2 gabbros echo the LREE production and loss of SO2, which fractionates S, even at enriched pattern of the Late Mull magma type. Kerr et al. (1999) high temperatures. Further decomposition and oxidation of used trace elements and Sr isotopes to show that the pyrrhotite resulted in hematite and/or magnetite within a recorded variations in composition were directly related to few cm of the contact. Iron sulphates were produced during magma chamber location and depth. Our new trace element cooling and oxidation within 20 cm of the contact. data appears to support these variable sources and our Pb Decarbonation of the sediments due to heating is also isotope data add weight to the concept that Centre 1 is more observed and is most clear at the upper contact of the sill, contaminated due to the initial intrusion of hot basic where carbon loss correlates with increasing δ 13C, material into ‘fresh’ Moine crust. The Pb and Sr data show consistent with loss of methane gas. The features observed that both the mafic and felsic rocks of Centre 2 have far less in the shales are consistent with a short-lived intrusion, Moine contamination. This may be due to faster ascent in an emplaced in <5 hours. The dolerite magma contains established plumbing system, reducing interaction times pervasive pyrite and localized sulphur concentrations between magma and crust. However, Centre 2 greater than the sulphur concentration at sulphide liquid geographically overprints Centre 1, meaning the magmas saturation, consistent with late-stage addition of sulphur would have traversed the same crust, which could have lost (perhaps from sediments) at a late stage. The sulphur the majority of its fusible components during the earlier isotope data does not show unequivocal evidence for (Centre 1) magmatism. Centre 3 is located 5km NW of the sulphur assimilation, but in order to explain the depletion in earlier two intrusions in ‘fresh’ crust and shows a 34S it is necessary to invoke degassing and/or assimilation of comparative increase in Moine contamination. No clear sedimentary sulphur. Our study provides evidence for evidence of lower crustal (Lewisian Gneiss) contamination desulphurisation, as well as decarbonation, of shales is seen, nor any indication of lateral magma transport from adjacent to an igneous intrusion. The liberated fluids, rich in the adjacent Grampian Highlands (Dalradian) terrane. sulphur and carbon, are likely to be focused along regions of low pore fluid pressure along the margins of the sill. This Kerr, A.C., Kent, R.W., Thomson, B.A., Seedhouse, J.K. & enhancement of the magmatic sulphur budget by sediment Donaldson, C.H. (1999) Geochemical evolution of the degassing has important implications for the climate impact Tertiary Mull volcano, western Scotland, Journal of of large flood basalt eruptions that erupt through thick, Petrology, Vol. 40, no. 6, pp873-908. volatile-rich sedimentary sequences. Questions remain regarding the mechanisms by which the fluids reach the surface, if at all, and whether it is through assimilation into the magma, or migration through fractures.

66 VMSG 2013 – Poster Presentation Abstracts

MORB like noble gas signatures The Snap Lake Kimberlite; A True within Western Antarctic Rift Zone Composite Intrusion

M.W. BROADLEY *1, C.J. BALLENTINE *1, R. BURGESS*1 R.A. BROOKER*1, R.C. OGILVIE-HARRIS1, T.M. GERNON2, R.S.J. SPARKS1, M. FIELD3 1 SEAES The University of Manchester, M13 9PL, UK (*[email protected]) 1 School of Earth Sciences, University of Bristol. (*[email protected]) The Western Antarctic Rift Zone (WARZ) represents a 2 School of Ocean & Earth Sciences. University of major area of Cenozoic extension between East and West Southampton. Antarctica. The rift has been exhibiting extensive volcanism 3 DiaKim Consulting Ltd, Wells, Somerset. since the middle Eocene to present and represents one of the Earths major extensional zones [1]. The cause of this large There is some debate in the literature regarding the scale extension is still subject to debate with both active and nature of the Snap Lake kimberlite intrusion (NW passive extension being proposed as the likely cause. Noble Territories, Canada). Field et al. (2009) have suggested it gas isotopes can provide new information on deep mantle represents two distinct magmas, one rich in ‘xenolithic’ processes which are driving the rifting. The noble gas olivine (ORK) and one olivine poor (OPK). These authors abundance and iotopic composition within 11 mantle suggest the ability to bring different amounts of xenolith from Northern Victoria Land have been determined ‘xenocrystic’ olivine load to the surface could be important to further our understanding of the WARZ. as a proxy for diamond grade and size distribution. In The fluid inclusion present within mantle xenolith contrast, Kopylova et al. (2010) suggested there was a provide the best medium through which magmatic volatiles single magma with variable degrees of alteration that impart can be transported to the surface and still be able to retain a the false impression of two phases of magmatism. The pristine magmatic signature [2]. The mantle xenoliths result of this study (part published in Gernon et al., 2012) analysed can be classified into three suites based on not only strongly supports the notion of two magmas, but location of discovery. All samples were located within also that these were intruded ‘simultaneously’ to give the alkali basalt dykes and they range in composition from first described example of a true composite kimberlite spinel peridotite to olivine – pyroxenite [3]. Samples were intrusion. Detailed field mapping, geochemistry and analysed for He, Ne and Ar using a VG5400 mass consideration of petrological differences on macro- and spectrometer. Samples were crushed in vacuo to release gas micro-scopic scales show how the two magmas intruded from fluid inclusion within the crystal and to avoid whilst still partially molten with ongoing loss of volatiles. releasing any radiogenic gas held within the matrix. Sample Careful analyses of the spatial distribution, texture and exhibiting alteration or addtion of cosmogenic nuclide were composition of phlogopite phenocrysts shows distinct excluded from this study. pressure-temperature histories for the two magmas and how The 3He/4He ratio extracted from the samples ranged they can be seen to mingle but stop short of full mixing. 3 4 from 6.25 – 8.68RA (RA = He/ He ratio of Air) with an Mixed batches of kimberlite magma may be more common average of 7.4RA this values is similar to the value that previously thought, but it is surprising that incomplete attributed to MORB mantle of 8RA ± 1RA. The samples mixing of two chemically similar compositions is preserved were found to also contain a 20Ne/22Ne ratio ranging from in the Snap intrusion. This might reflect the rapid timscale air to 11.85. With 40Ar/36Ar ratio measured ranging from of intrusion and solidification. 309 to 1139. All isotopic ratios measured fall within a MORB like mantle signature with the addition of an air Field, M. et al., (2009) Lithos 112S, 23-35. derivived component. Kopylova et al. (2010) Canadian Mineralogist 48, 549-570. This combined noble gas signature greatly differs from Gernon et al., (2012) Journal of the Geological Society 169, that found in Plume source material with the 3He/4He ratio 1-16. of plumes ranging from 12 - 50RA[4] and therefore the role of plume driven rifting can be ruled out in this case. The ratios within the xenoliths also differs from the value obtained from other rift zones which are thought to have sampled the Sub Continental Lithospheric Mantle (SCLM) 3 4 with the He/ He ratio of 6.1RA ± 0.9RA [5] noticeably differing from the values obtained from the WARZ samples. The data obtained within this study suggestes that the rifting seen within Antarctica has evolved past the point of passive lithospheric melting and is now dominated by active upwelling of MORB like mantle.

[1] Nardini et al. (2009) J. Pet 50 1359 – 1375. [2] Burnard et al (1994) J. Geophy. Res 99 17,709 – 17,715. [3] Perinelli et al (2011). 52 665 – 690. [4] Stuart et al (2003). Nature 424 57 – 59. [5] Gautheron and Moreira (2002). EPSL 199 39 – 47

67 VMSG 2013 – Poster Presentation Abstracts

Vesiculation of a rhyolitic melt: Trace element systematics of zircon New insights from hot-stage from I- and S-type granites

microscopy experiments A.D. BURNHAM*1,2, A.J. BERRY1,3, I.S. WILLIAMS3, R.B. ICKERT4 J. BROWNING*1, H. TUFFEN1, M. JAMES*1 1 Department of Earth Science and Engineering, Imperial 1 Lancaster Environment Centre, Lancaster University. College London (*[email protected]) (*[email protected]) 2 School of Earth Sciences, University of Bristol.

3 Research School of Earth Sciences, Australian National Although pumice is an end-member product of gas-rich University, Canberra. explosive volcanism, the process of bubble growth which 4 Berkeley Geochronology Center, California 94709, USA. leads to the formation of pumiceous textures are not well constrained. Vesiculation in rhyolitic melts is a primary Zircon is an invaluable accessory mineral because it control on some of the largest explosive eruptions. This provides robust determinations of magmatic ages and study presents the results of a series of experiments which withstands subsolidus and hydrothermal alteration, thereby have utilised hot-stage microscopy techniques to track recording geochemical and thermobarometric data indelibly. vesicle growth in an initially vesicle-poor rhyolitic melt. Detrital zircons (e.g. Hadean grains from the Jack Hills) can Using rhyolitic obsidian erupted from Chaiten, Chile in only provide information about their parental magmas 2008 (containing ~1.38 wt. % H2O), thin wafers were held where there are well-characterised natural and experimental at atmospheric pressure for periods of between 5 minutes oC samples to compare to. Rare earth element patterns in zircon and 2 days in the hot-stage, at temperatures between 575 oC. have been shown to reflect the oxidation states of their host and 875 In-situ vesiculation was directly observed and rocks, though Ce and Eu can be decoupled by crystallisation the growth of individual bubbles measured using image of feldspars, which readily incorporate Eu2+. Bulk rock Fe tracking code in MATLAB. It was found that bubble growth oxidation state ratios, Fe-Ti oxide systematics and S rates increased with both temperature and bubble size. The oC concentrations in apatite all indicate that S-type granites are average growth rate at the highest temperature of 875 is generally more reduced than I-type granites (Chappell & ~1.27 mm s-1, compared with the lowest observed growth oC; White, 2001). This study presents data from zircons rate of ~0.02 mm s-1 at 725 below this temperature, no separated from granites (sensu lato) of the Lachlan Fold growth was observed. Average growth rate Vr follows an Belt, Australia, to assess the extent to which source and exponential relationship with temperature and melt viscosity process can be identified from Ce, Eu and other trace where Vr ≈ exp (0.0169T) and Vr ≈ exp (-1.202m). The element systematics of populations of crystals. extent of diffusive degassing from wafer surfaces was Trace elements in zircons from a range of I- and S-type estimated with simple diffusion models. Diffusive loss was granites from the Lachlan Fold Belt, Australia (selected to found to be negligible during brief high-temperature cover a range of ages, major element and isotopic experiments but became increasingly important in slower, compositions) were analysed by laser ablation mass lower temperature experiments. Several stages of bubble spectrometry. Simultaneous U-Pb age determination growth were directly observed, including initial relaxation allowed inherited (xenocrystic) crystals to be identified and of deformed existing bubbles into spheres, extensive growth disregarded. of spherical bubbles, and, at higher temperatures, close Ce anomalies in zircons from the I-type granites were packing and foam formation. An advantage of the imaging larger by a factor of ~10, indicating that the oxygen fugacity techniques used here is that bubble-bubble interactions can of these magmas was ~4 orders of magnitude higher. be observed in-situ at a scale of 2 to 3 microns. Evolving Despite multiple recent attempts to calibrate this bubble number densities (BND) with time were determined, oxybarometer (Trail et al., 2011; Burnham and Berry, 2012; allowing nucleation rates to be estimated. Maximum Trail et al., 2012), further work is required to interpret the observed BNDs were 3.4 × 1012 m-3 with maximum Ce anomalies fully. Surprisingly, there is a systematic increases of around 160 % observed in samples with lower difference between the Eu anomalies in the two granite initial vesicularity (< 5.7 × 1011 m-3). Experimentally types (more negative in the S-type granites). This is likely determined rates of nucleation, growth and coalescence to be due to the relative oxidation states of the melts, and assist in the reconstruction and vesiculation history of suggests that the Eu anomaly records redox information quenched products and in models of magma vesiculation at despite the influence of plagioclase on the Eu budget of a shallow levels. magma. Differences in the abundances of other elements, including U, Th, Li, P, and Hf will also be discussed with reference to the relative contributions of source composition and magmatic differentiation for these variations.

Burnham and Berry (2012). Geochimica et Cosmochimica Acta 95, 196-212. Chappell & White (2001). Transactions of the Royal Society of Edinburgh 83, 1-26. Trail et al. (2011). Nature 480, 79-82. Trail et al. (2012). Geochimica et Cosmochimica Acta 97, 70-87.

68 VMSG 2013 – Poster Presentation Abstracts

A tale of two magmas: Petrological Dynamics of deforming partially insights into mafic and intermediate molten regions and the nucleation of explosive volcanism at Volcán de dykes

Colima, Mexico M. DIEZ*1, J. BLUNDY2, A. HOGG3 J.M. CRUMMY*1, I.P. SAVOV1, D.J. MORGAN1, M. 1 Shcool of Earth Sciences. University of Bristol. WILSON1, C. NAVARRO-OCHOA2, S. LOUGHLIN3 (*[email protected]) 2 School of Mathematics. University of Bristol 1 Institute of Geophysics & Tectonics, School of Earth &

Environment, University of Leeds, Leeds, UK. The dynamics of deforming partially molten regions at (*[email protected]) different tectonic boundaries is an outstanding problem 2 Observatorio Volcanologico de Colima, Universidad de involving the crossing of many spatial scales, from melt Colima, Colima, Mexico. pockets to much larger transport structures. These regions 3 British Geological Survey, Edinburgh, UK. are the source for a large volume of the magmatism occurring in the planet. Thus, their dynamics plays an Volcán de Colima in western Mexico explosively erupts important role on volcanism and plutonism, specifically basalt to high-silica andesite magmas. Detailed petrological through processes leading to dyke formation. In the last two and geochemical analyses of Holocene tephra fallout decades or so, field studies of exposed lower crustal deposits reveal two distinct magma types: I. typical calc- migmatitic domains, cooling and deforming intrusive bodies alkaline series magmas; and II. mixed calc-alkaline - and fossil arcs reveal that partially molten regions organize alkaline magmas. Group I magmas comprise basalt to high- from pore micron-scale into centimetre-size bands, leading silica andesite (50.7 to 60.4 wt.% SiO ) and typically 2 to meter-size transporting dikes. Experiments on deforming contain phenocrysts of plagioclase + clinopyroxene + synthetic aggregates in simple shear also confirm the orthopyroxene + Fe-Ti oxides ± hornblende ± olivine. organization of partially molten mixtures into shear bands. Crystallinity varies from 10-25 vol.% dominated by Even though dyke propagation has been intensively studied, plagioclase in a groundmass comprising highly vesiculated processes governing the previous stage of dike initiation glass with abundant microlites. Back-scatter electron (BSE) still remain poorly known. These processes control the microscope images together with electron microprobe initial dimensions of the dike and thus will have a large analyses (EPMA) reveal complex zoning patterns and impact on its propagation dynamics once it leaves the compositional variations in plagioclase and pyroxene source. We look for a theory that accounts for the time and phenocrysts which have been interpreted to have resulted spatial scales inferred from field and experimental studies. from a complex crystallisation history involving multiple We propose that in this theory dike initiation occurs through magma mixing and decompression events. a nucleation stage governed by melt segregation and Group II magmas comprise basalt to basaltic-andesite compaction within a deforming mixture. This stage would (48.3 to 57.5 wt.% SiO ) and contain 10-15 vol.% crystals 2 be followed by the comparatively better understood comprising clinopyroxene + olivine + phlogopite + propagation stage, mainly governed by channel flow. In this plagioclase + Fe-Ti oxides ± hornblende ± orthopyroxene. study we focus on the first nucleation stage. We make use The groundmass comprises highly vesiculated glass with of two-phase theory for mixtures undergoing shear flow, abundant microlites of the same mineral phases. and derive solutions in pure shear. Dyke nucleation and the Clinopyroxene and olivine phenocrysts have high-Mg cores role of damage is then explored in different conditions, such (Mg# 88-89) that display strong dissolution with clear as stretching host-rocks on top of diapiric upwellings and resorption and recrystallisation. EPMA analyses reveal lithospheric regions undergoing extension. large compositional differences with the surrounding growth zone (Mg# 80) indicating recrystallisation and re- equilibration within a compositionally different melt. This composition of the clinopyroxene is similar to that of the Group I magmas. Whole-rock geochemical and Sr and Nd isotopic analyses reveal strong trends in the Group II magmas towards the composition of monogenetic cinder cones composed of phlogopite-bearing alkaline lamprophyre situated to the north of Volcán de Colima. The alkaline magmas are thought to have formed from partial melting of metasomatically enriched veins within the lithospheric mantle. We suggest the high Mg clinopyroxene cores of the Group II magmas crystallised from such alkaline melts, which then mixed with the parental mantle-derived melts of the Group I magmas.

69 VMSG 2013 – Poster Presentation Abstracts

The Red Hills Intrusive System: The structure and evolution of Easternmost porphyry copper shallow magmatic systems emplaced deposit in southwestern North in fold-and- thrust belts – a case America study of Cerro Negro, Neuquén A.K. GILMER*1, J.R. KYLE2 Province, Argentina 1 Virginia Div. of Geology and Mineral Resources. D. GÜRER*1, F. CORFU2, O. GALLAND1 (*[email protected]) 1 Physics of Geological Processes (PGP), University of 2 Department of Geological Sciences, Jackson School of Oslo, Oslo, Norway. (*[email protected]) Geosciences, The University of Texas at Austin. 2 Department of Geoscieces, University of Oslo, Oslo, Norway. The Red Hills intrusive system hosts the easternmost Laramide porphyry copper deposit in southwestern North In contrast to the classical concept of magma ascent in America. The Red Hills pluton crops out near the southern extensional settings, recent studies show that volcanism also margin of the 32-Ma Chinati Mountains caldera. Zircon U- occurs in compressional settings. The nature of the interplay Pb, molybdenite Re-Os, and sericite 40Ar/39Ar analyses yield between magmatism and tectonics in fold-and-thrust belts ages of 64, 60, and 61 Ma, respectively, indicating that the however, remains a major question, notably in active Red Hills magmatism and mineralization are distinctly older margins. The mechanisms of magma transport in such than other Cenozoic magmatism (48–17 Ma) in Trans-Pecos settings and whether magmatism affects tectonic Texas. The Red Hills intrusive system is contemporaneous deformation need to be addressed. with and genetically related to other Laramide magmatic Therefore, we carried out detailed structural mapping systems (75–54 Ma) that host porphyry copper deposits in and sampling of the Cerro Negro intrusive complex, at Arizona, southwestern New Mexico, and northern Mexico. Tricao Malal, Neuquén Province, Argentina. This intrusive These results significantly extend the Laramide magmatic system belongs to a magmatic province in the Agrio fold- province eastward and suggest that Laramide subduction- and-thrust belt, located between 37°S and 38°S in the related magmatism and deformation are coextensive over a Argentinean foothills of the Andes. The fold-and-thrust belt broad area of southwestern North America. has resulted from intense E-W shortening, and contains Fluid inclusion studies of the mineralized quartz tight folds and thrusts, trending N-S. The intrusive complex stockwork in the Red Hills quartz monzonite constrain crops out as a network of sills and dykes around a main pressures from 20 to 30 MPa, corresponding to depths of intrusion, all of which are of andesitic composition. formation of 2 to 3 km. Estimated salinities for the fluid The Cerro Negro plumbing system is well exposed so inclusions from quartz veins associated with phyllic that the relations between the intrusions and the tectonic alteration range from 33 to 47 wt. % NaCl equiv. The high structures can be studied. We have identified at least two salinities of these fluids suggest a magmatic source. geometries of intrusion: sills that have been folded in an

open anticline, and subvertical dykes that strike N-S, i.e. Gilmer, A, K., Kyle, J. R., Connelly, J. N., Mathur, R. D., perpendicular to the shortening. According to field Henry, C. D., (2003) Geology Vol 31, page 447-450. observations, the main intrusive body and the dykes have Gilmer, Amy K., (2001) Age and characterization of the formed in a central anticline, the dykes being close to the Red Hills porphyry copper-molybdenum deposit and its hinge, suggesting that there is a structural control on magma relationship to the Chinati Mountains caldera, Presidio emplacement. Furthermore, the dykes locally crosscut the County, Texas. University of Texas at Austin, MS. folded sills. No deformation has been observed in the dykes, thesis, 213 pages. possibly due to their location close to the anticlinal hinge.

This suggests that sills predate or are coeval with deformation, whereas dykes postdate deformation. From the structural and temporal relationships between the anticline and the dykes we infer that local stresses controlled the formation of the dykes during outer-arc stretching. This illustrates how tectonic deformation may control magma emplacement. Conversely, the traces of the main tectonic structures curve around the intrusive complex, suggesting that the latter influenced the tectonic deformation. New U-Pb data for zircons for both dykes and sills yield ages of 11-12 Ma, indicating that the lifetime of the magmatic system was less than 1 m.y. Absolute dating confirms that the dykes were emplaced during a time of active shortening. This study contributes the first robust evidence of substantial regional shortening at least until 11 Ma in the area.

70 VMSG 2013 – Poster Presentation Abstracts

Water/rock interaction and volcanic Experimental insights into the behavior formation of amphibole reaction

B. HEMMINGS*1, A. JASIM1, F. WHITAKER1, B. BUSE1, rims: Texture, mineralogy, and J. GOTTSMANN1 processes of formation 1 University of Bristol (*[email protected]) S. HENTON DE ANGELIS*1, J. LARSEN1, M. COOMBS2,

A. DUNN3 Hydrology is of key importance in volcanic island settings. On the volcanic Caribbean island of Montserrat its 1 Geophysical Institute, University of Alaska Fairbanks. importance is evident: storm rainfall can trigger landslides, (*[email protected]) mudflows and devastating flooding but it also recharges the 2 Alaska Volcano Observatory, U.S. Geological Survey aquifers of the extinct Centre Hills (CH), which supply (USGS). drinking water for the entire island. Within the active 3 Department of Geology and Geophysics, University of Soufriere Hills Volcano (SHV), superheating of circulating Alaska Fairbanks. fluids can produce explosive phreatic eruptions and the chemical interaction of these fluids with the edifice rocks Amphibole is an important mineral present in many can lead to flank weakening and potentially catastrophic calc-alkaline volcanic deposits. A hydrous phase, volcanic collapse. However, the very presence of an active amphibole is only stable at pressures greater than ~100 MPa hydrothermal system provides an attractive target for (approx. 4 km) and in melts containing at least 4 wt % H2O. geothermal energy development. In order to mitigate the When removed from their thermal and barometric stability hazards and effectively exploit the resources associated with field, amphiboles decompose to form aggregate rims of the hydrological and hydrothermal systems it is critical to anhydrous minerals. Reaction rim thicknesses have been understand the fundamental physical and chemical used to estimate timescales and rates of magma ascent, an interactions that occur in the development and propagation important parameter in determining eruptive style. of such systems. However, the process of reaction rim formation is complex; The progression of volcanic activity on Montserrat from numerous magmatic properties exert a control on the north to south over ~2.5 Ma provides a unique insight into reaction process (e.g. magma compositions and viscosities) the temporal behavior of a system from the building of a and multiple forcing factors may be responsible for their volcanic edifice, composed of a lava core surrounded by formation (e.g. heating, decompression, or changes in volcaniclastic aprons (SHV), to the eventual erosion back to magma chemistry). Few studies have performed in-depth, the central core of an extinct volcano (Silver Hills, SH). systematic, and quantitative investigations of reaction rim This transition results from an interplay between physical textures and mineralogy: as a result, amphibole reaction and chemical processes that vary both temporally and rims are poorly understood. We present the results of an in- spatially. Episodic and intense storms incise and erode the depth experimental study into the formation of amphibole variably consolidated volcaniclastic deposits, transporting reaction rims. The experimental series took samples to material seaward via ephemeral rivers. These storm events differing degrees of thermal of barometric instability, over also have the potential to trigger volcanic hazards such as different time scales, ranging from 3 – 144 hours. The dome collapses and pyroclastic flows, as well as lahars. resulting reaction rims were analyzed using a variety of However, the physical processes are affected by water- analytical imaging and X-ray mapping techniques. We find rock interactions which modify the physical properties of that a range of different processes can contribute to the rocks and deposits, such as hydrothermal weakening of the formation of reaction rims. A key result is that the edifice and reduction of slope stability. Chemical reactions mineralogical and textural features of many experimental between circulating fluids (both meteoric and hydrothermal) heating-induced amphibole reaction rims are and country rock also have a dramatic effect on indistinguishable from natural reaction rims attributed by permeability and porosity, with important implications for past studies to decompression (and subsequently used to the ongoing maturation of the hydrological system and the infer magma ascent rates). eventual distribution of aquifer and aquitard units. The nature and product of the chemical interactions depend on climatic and topographic controls, but also the thermal and chemical conditions. Chemical processes evolve as the volcanic activity and thus the hydrothermal activity wanes. For example, on the active SHV hydrothermal alteration is dominant, locally leading to complete destruction of the igneous texture, while on the neighboring extinct CH (0.5 Ma older) meteoric weathering dominates. While the distribution of meteoric weathering is potentially controlled by the hydrothermal alteration history, it is also capable of over-printing its signature. Through field observations, sample examination, reaction experiments and numerical modeling, we explore development and maturation of hydrological systems on Montserrat.

71 VMSG 2013 – Poster Presentation Abstracts

Changes in heavy metal distribution Platinum group element and deposition at Poás Volcano, geochemistry of the Scourie Dykes: Costa Rica Insights into the Lewisian

M. HINRICHS*1, H. RYMER1, S. BLAKE1, M. GILLMAN1 subcontinental lithospheric mantle 1 Environment, Earth and Ecosystems, The Open University, H.S.R. HUGHES*1, I. MCDONALD1, Walton Hall, Milton Keynes, MK7 6AA A.C. KERR1 (*[email protected]) 1 School of Earth and Ocean Sciences, Cardiff University, Activity at Poás volcano, Costa Rica, is characterised by Park Place, Cardiff, UK. CF10 3AT. periodic cycles of activity. The volcano entered its current (*[email protected]) phase in 2008, since when there has been a steady increase in the level of activity. There has been a build up in gas flux Increasing awareness of ‘critical metals’ such as the and this has led to an increased deposition of heavy metals. platinum group elements (PGE) has seen renewed The deposition of these heavy metal plume components, exploration effort for these elements. This research forms and their incorporation into soil, is of key interest because part of a larger investigation into the potential for Ni-PGE soils act as geochemical sinks. Once discharged to the mineralisation in western Scotland and Northern Ireland, environment heavy metals can accumulate and be a incorporating Archaean, Caledonian, and Palaeogene lavas potential source of contamination for plants and animals and magma conduits in an attempt to understand the (Alloway, 1995). underlying factors controlling mineralisation. This study investigates the pattern of heavy metal The NW-SE trending Scourie Dyke swarm comprises a transport, deposition and distribution in Poás soils over a variety of deep-seated mafic and ultramafic dykes, intruded period of two years (2010- 2011). Soils of agricultural and into the Lewisian tonalite trondhjemite granodiorite non-agricultural sites at two horizons (0-10 cm and 20-30 foreland at the end of the Ivernian deformation, between cm) were collected and their trace element content analysed. 2.42 to 2.38 Ga (Davies et al., 2012). Samples were taken from eleven sites between the active Dyke samples have been collected from across the vent and ~6 km downwind, as well as from two control sites mainland Lewisian foreland, encompassing a variety of that were unaffected by the activity. dyke types (Tarney & Weaver, 1987) including picrite, None of the metals analysed (Fe, Cr, Cu, Mn, Ni, Zn, olivine gabbro, and dolerite suites. All 72 samples collected Se, As and Hg) showed a concentration above guideline were analysed for major and trace elements, and a thresholds. However, concentrations increased during the representative selection of 32 samples were assayed for bulk sampling period, suggesting changes in metal distribution PGE. Prior to this investigation, few analyses existed of the and concentration as a result of the increase in volcanic Scourie Dykes, with only 5 published PGE analyses (Frick activity. Concentrations generally increased with distance et al., 1994). This research now forms the most away from the active vent, and were highest in the comprehensive geochemical database of Scourie Dykes to agricultural soils 4-6 km downwind of the source. Heavy date. metal concentrations in the soils from the control sites were All dyke groups display normalised rare earth element lower than the sites affected by the active vent, confirming (REE) patterns that are moderately enriched in the light that the plume is a contributing factor to the total metal REE, however the picrite and olivine gabbro dykes are most content. Widespread increases of metal concentrations in enriched in light REE. The dolerite group dykes have flatter agricultural soils caused by long-range transport of REE patterns, but the highest total REE concentrations. All contaminants are therefore a risk that needs to be dykes are enriched in large ion lithophile elements (some of considered. which may be caused by variable dyke alteration) and depleted in high field strength elements. Alloway, B.J., (1995), Soil processes and the behaviour of Total PGE+Au concentrations range from 38.3 ppb heavy metals. In: Heavy Metals in Soils, Blackie (olivine gabbro group) to 2.7 ppb (dolerite group). All Academic and Professional, London. 11-37. dykes show fractionated PGE trends, enriched in Pd-group PGE (PPGE). Dolerite dykes show a marked depletion in Ir- group PGE (IPGE), indicating a lower degree of mantle melting, leaving a significant residue of Ir-Os alloys in the source. Chalcophile element ratios (e.g. Cu/Pd) are typically higher than estimated primitive mantle, suggesting that the Archaean subcontinental lithospheric mantle underwent low degrees of partial melting thereby contributing low concentrations of PGE to the S-undersaturated parental magmas of the Scourie Dykes.

Davies, J.H.F.L., et al. (2012) Goldschmidt Conference. Frick, L.R., et al. (1994) Goldschmidt Conference. Tarney, J. and Weaver, B.L. (1987) Geological Society Special Publication Vol. 27, pp. 217-233.

72 VMSG 2013 – Poster Presentation Abstracts

Fe3+/ΣFe in hydrous glass Depositional and textural M.C.S. HUMPHREYS*1, R.A. BROOKER2, D. G. characteristics of “dry” maar FRASER1, V.C. SMITH3 volcanoes in northern Tanzania 1 Department of Earth Sciences, University of Oxford, South H.B. MATTSSON*1 Parks Road, Oxford, OX1 3AN, UK (*[email protected]) 1 Institute of Geochemistry and Petrology, Clausiusstrasse 2 School of Earth Sciences, University of Bristol, Wills 25, ETH Zurich, 8003 Zurich, Switzerland. Memorial Building, Queen’s Road, Bristol, BS8 1RJ, (*[email protected]) UK 3 Research Laboratory for Archaeology and the History of Many of the apparent phreatomagmatic landforms in Art, Dyson Perrins Building, South Parks Road, Oxford, northern Tanzania lack the classical evidence for OX1 3QY, UK phreatomagmatic fragmentation and/or deposition (such as accretionary lapilli, plastering against obstacles, vesiculated The Fe oxidation state of arc magmas, and the Fe3+ tuffs, etc.). Instead, the landforms are dominated by fluidal contents of spinels in primitive arc basalts, are typically shaped pyroclasts and dry deposition (e.g., efficient grain- much higher than in mid-ocean ridge basalts. This has been size segregation in the eruptive plume and depositional interpreted by some as a result of the transfer of slab- characteristics indicative of grain-flow). In addition to this, derived components into the mantle wedge (Evans et al. the eruptive centers are predominantly located on top of a 2012), and by others as the result of differentiation or late- horst structure (i.e., the Kerimasi block) in an arid stage degassing processes within the arc crust (Lee et al. environment where evaporation greatly exceeds rainfall on 2010). Recent studies have reported a correlation between an annual basis. Thus, the source of water required to drive 3+ 2+ Fe /Fe and H2O in primitive arc melt inclusions, the phreatomagmatic fragmentation process is unclear in suggesting a clear link between slab components and this area of the East African Rift. However, because of the oxidation state (Kelley & Cottrell 2009). It is clear that the geochemistry of the magmas involved (predominantly volatile contents of melts may re-equilibrate very rapidly, melilititic in composition) the vigor of the eruptions and the 3+ 2+ but the effect of changing H2O on Fe /Fe is unclear. high degree of fragmentation can be attributed to rapid We present data that suggest that observed correlations exsolution of CO2 during ascent of the melilititic magmas. 3+ 2+ between H2O and Fe /Fe can be expained in part by These types of magmas have been shown experimentally to considering the acid-base proprties of the melt (Fraser be able to hold up to 18 wt.% CO2 dissolved within the melt 2005). In particular, basic behaviour of FeO and amphoteric structure at upper-mantle pressures (Brooker et al., 2001), behaviour of Fe2O3, combined with changes in melt basicity and it is likely that delayed nucleation during rapid relating to dissolution of H2O, can explain increasing Fe decompression resulted in massive exsolution of CO2 which oxidation state with increasing H2O. We discuss the may explain the highly explosive character of these implications of these results for using melt inclusions to “apparently phreatomagmatic” landforms. investigate the oxidation state of the earth’s mantle. Brooker, R., A., Kohn, S., C., Holloway, J., R., McMillan, Evans, K. et al. (2012) Geology doi: 10.1130/G33037.1 P., F., (2001) Chemical Geology 174, 225-239. Fraser, D.G. (2005) Annals of Geophysics 48, 549-559 Kelley, K.A. & Cottrell E. (2009) Science 325, 605-607 Lee, C.T. et al. (2010) Nature 468, 681-685

73 VMSG 2013 – Poster Presentation Abstracts

Temporal geochemical changes in The source of A-type magmas in the Miocene Ignimbrite succession two contrasting settings: on Gran Canaria: Crustal Constraints on processes and contamination or mantle tectonics from U–Pb, Lu–Hf and heterogeneity? Re–Os isotopes

P. NICHOLLS1, V. TROLL1,2, B. ELLIS3, A. BARKER1, I. PANKHURST, M.J.*1,2, SCHAEFER, B.F.1, TURNER,S.P.1 BINDEMAN4 1 GEMOC, Macquarie University, Sydney 2109, Australia. 1 Department of Earth Sciences (CEMPEG), Uppsala 2 School of Earth & Environment, University of Leeds, UK. University, 75236 Uppsala, Sweden (*[email protected]) 2 Departamento de Física (GEOVOL), Universidad de Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, We observe a convergence of process within two Canary Islands, Spain. different geodynamic generating post-orogenic, high- 3 ETH, Swiss Federal Institute of Technology, Zurich, temperature, A-type magmas. The production of these Switzerland distinctive magmas and concomitant formation of stable 4 Dept. of Geological Sciences 1272 University of Oregon lithospheric domains is suggested to be the key factor for 1) Eugene, OR 97403-1272, USA ending orogenesis and 2) producing stable ‘pinning’ blocks that influence subsequent tectonic evolution. The end of the Recent work by Bindeman et al (2008) on the ca. 514 – 480 Ma Delamerian Orogeny, southeastern South Yellowstone system has postulated the progressive Australia, is marked by ~10 Myr of bimodal A-type assimilation of crustal volcanic material into the magmas magmatism. Mostly felsic products were emplaced at that fed large scale silicic explosive eruptions. This is shallow crustal levels, and outcrop in an ~300 km arc recorded in oxygen isotopes of the eruptive products. Gran coincident with a gravity high, interpreted as voluminous Canaria hosts a long-lived volcanic system which mafic intrusives at mid crustal levels. Here Re–Os and Lu– incorporates shield basaltic lavas and an extensive Hf isotope ratios record a dominantly juvenile lithospheric succession of Miocene silicic ignimbrites and lavas (the mantle source, from which mafic parental melts fractionated Mogan and Fataga formations, > 1400km3). These to produce the granites. Raised lithospheric temperatures ignimbrites were sampled for oxygen isotopes to see were caused by in-welling of aesthenosphere that followed whether the Gran Canarian magmas were influenced by a convective thinning of an unstable (thickened) lithospheric similar assimilation process or whether temporal changes in column, along the strike length of the orogeny. In contrast, the mantle compositions, as proposed by previous workers Re–Os and Lu–Hf isotope ratios of the A-type magmas that (eg Cousens et al 1990). comprise the ca. 1598 – 1583 Ma Mesoproterozoic Gawler Oxygen isotopes show a progressively more negative Felsic Large Igneous Province, central South Australia, excursion up section (14-12 Ma) which confirms that in the record a dominant evolved lower crust component mixed late stage of the Miocene cycle a change in the magma with small amounts of juvenile lithospheric mantle. Plume composition feeding the eruptions occurred. These more head arrival resulted in a regionally elevated geotherm, negative values are consistent with similar trends described driving partial melting of the most fusible portions of the by Bindeman. However, it is also noted that Strontium upper lithosphere. This produced rapid, voluminous, isotope ratios decrease at around the same time while Pb bimodal magmatism that lasted for ~15 Myr, and ended the isotopes show correlated excursions too. These observations Wartakan Orogeny. These two end member case studies appear to point towards a mantle source change being more highlight the observation that A-type magmatism is always plausible than crustal contamination as the latter would transient. The contemporaneous fusion of both mantle and likely produce an increase in strontium isotope ratios rather crust represents a common, stabilizing influence on the than a decrease. This appears to indicate that crustal lithospheric column regardless of tectono-magmatic setting. contamination played little part in the later stages of Miocene activity on Gran Canaria, and that oxygen- strontium isotope correlations suggest a change in mantle source. This would reflect a change from a mixed source involving EM1, DMM and HIMU to a higher proportion of the HIMU-like component towards the end of Miocene activity , likely a function the waning of the EM1-like component in the supply column.

Bindeman et al. (2008) J. of Petrology, 49, pp. 163-193. Cousens et al. (1990) Earth Planet Sci Lett, 96, pp. 319- 335.

74 VMSG 2013 – Poster Presentation Abstracts

Sm-Nd and U-Pb isotope The lattice strain model applied to geochemistry of the Sweetwater coexisting garnet and clinopyroxene

Wash and North Piute plutons, J. PICKLES *1, J. BLUNDY 1, C.B. SMITH1 Mojave Desert, California 1 University of Bristol. (*[email protected])

S. PHILLIPS*1, J. HANCHAR1, C. MILLER2 Understanding the behaviour of elements and minerals 1 Department of Earth Sciences, Memorial University of subducted into the mantle is important in helping to Newfoundland, St. John's, NL Canada A1B 3X5 interpret the behaviour of volatiles and processes in the (*[email protected]) overlying mantle wedge. Through high-pressure and high- 2 Earth & Environmental Sciences, Vanderbilt University, temperature experiments we investigate the behaviour of Nashville, TN 37235-1805, USA elements, specifically how elements partition between garnet and clinopyroxene in the subducting slab. In situ analyses of the isotopic and trace element The lattice strain model (Blundy and Wood, 1997) was composition of minerals at the sub-grain scale have proven developed on, and is routinely applied to, the partitioning of to be effective tools for understanding the origins and elements between a mineral and its equilibrium melt. In evolution of magmatic systems. The ability to this study we investigate the applicability of the lattice simultaneously measure Sm-Nd and U-Pb isotopes by LA- strain model when applied to the partitioning of rare earth ICP-MS allows a high-resolution spatial and temporal elements (REE) between garnet and clinopyroxene (cpx). snapshot of crystallisation history. We also investigate the potential of the lattice strain model The late Cretaceous Sweetwater Wash Pluton (SWP) in being utilised as a geothermometer. the Mojave Desert, California, provides an excellent The data generated in this work are combined with oppurtunity to utilise these techniques in order to published experimental data to compare the thermodynamic understand the petrogenesis of continental arc granites. This theory and the experimental data. We show that lattice peraluminous granite is well understood in terms of major strain model theory accurately predicts the experimental & trace element geochemistry (Mittlefehldt & Miller) and data. We develop new terms allowing the calculation of the accessory phase geochemistry (Wark & Miller). A Youngs modulus and ideal cation size through the major preliminary study of monazite in the SWP (Fisher) suggest element composition without needing to know either that the εNd signature of the source region is retained temperature or pressure. We show that the lattice strain (~1700 Ma) yet U-Pb ages show an isotopic resetting during model can be used to calculate temperature for the emplacement at ~75Ma. Mineral scale heterogeneity also experimental data. However, the accuracy of the demonstrates extrememe isotopic disequilibrium in temperature prediction is highly dependent on the Youngs monazite and titanite, whereas REE concentrations are modulus of the garnet. To circumvent this issue we also consistant with closed-system fracational crystallisation present an empirical thermometer based on the REE The current study is aimed at using these geochemical partitioning between garnet and cpx. Both models have a tools to further constrain the petrogenesis of the SWP and greater accuracy than the widely used geothermometer of place it in its regional context. Upcoming fielwork involves Ellis and Green, 1979. systematic sampling throuhg a transect of the pluton to examine the spatial changes from the edge to the centre of Blundy, J.D. and Wood, B.J. (1994) Nature 372, 452-454. the pluton as recorded in monazite and zircon. Ellis, D. and Green, D. (1979) Contributions to Mineralogy and Petrology 71, 13-22. Mittlefehldt, D.W. and Miller, C.F. (1983) Geochemica et Cosmochemica Acta, 47, pp. 109-124. Wark, D.A. and Miller, C.F. (1993) Chemical Geology, 110, pp. 49-67. Fisher, C.M. (2011) Unpublished PhD. Thesis.

75 VMSG 2013 – Poster Presentation Abstracts

The role of ice cavities in lava lobe Phreatomagmatic edifices produced formation by lava-sediment interaction

H. REYNOLDS*1, D. WOODCOCK1, J. GILBERT1, S. P. REYNOLDS1*, R. BROWN1, E. LLEWELLIN1, T. LANE1 THORDARSSON2, K. FIELDING3, 1 Lancaster Environment Centre, Lancaster University, 1 Dept. Earth Sciences, Durham University, Science Labs, Lancaster LA1 4YQ. (*[email protected]) Durham, UK. DH1 3LE (*[email protected]) Lava lobes are small volcanic features (~ 10 m high) 2 School of GeoSciences, University of Edinburgh, which have been observed at various locations in Iceland Edinburgh EH9 3JW and at Nevados de Chillán, Chile. However, the mechanism 3 Level 9, The Adelphi Building, 1-11 John Adam Street, for the creation of lava lobes remains controversial. It is London WC2N 6AG plausible that lava was emplaced within pre-formed ice cavities which were themselves generated by volcanic Rootless cones are formed during the explosive fumaroles. This study investigates the feasibility of this interaction of pāhoehoe lava and unconsolidated substrate. theory using an analogue experimental approach. The Previous studies have focused on the architecture of cone generation of ice cavities by fumarolic activity was groups and proposed generic models for the formation of investigated on a laboratory scale and an experiment was cones, without a detailed assessment of their lithofacies designed to observe and quantify the physical processes architecture. This research in progress aims to determine the which took place. All significant heat transfer processes physical volcanology of a dissected rootless cone, and were considered and a model of the melting process was determine how the preserved deposits can be used to infer constructed based on experimental observations. The lava flow substrate conditions. Field studies in the laboratory-generated cavities were found to most closely Columbia River Flood Basalt Province, Western USA, resemble a truncated prolate spheroid in morphology. Lava detail transitions from Surtseyan-style tephra jetting to lobes are commonly conical; various processes are Hawaiian fire fountaining within individual edifices, likely suggested to explain the difference between the field to be the result of decreasing water:magma ratios with time. observations and those observed in the laboratory. A cavity The explosive brecciation of host rock, sub-flow quenching growth rate of 1.8 x 10-4 m3 s-1 was estimated using of pyroclasts and admixture of substrate material are also experimental data. This equates to a period of 6 x 105 s to found to be important facies-forming processes. These generate an ice cavity (4 m in height), which is realistic processes highlight previously unrecognised complexity when compared to the ascent time of rhyolitic magma. This during the growth of rootless cones arising from subtle study discusses the major contributing factors which affect variations in substrate conditions. Intimate mixtures of cavity growth and morphology including: meltwater contact metamorphosed substrate and spatter fall deposits drainage; debris and impurities within the ice; fumarole within the cone also have implications for the interpretation dynamics, and ice deformation. Experimental data obtained of peperitic textures in other volcanic settings. This study during this study could be used to calibrate more forms part of a wider project detailing the architecture of sophisticated analogue or numerical models of the physical fissure derived products in Flood Basalt settings. processes of fumarolic ice melting.

76 VMSG 2013 – Poster Presentation Abstracts

Concentrations of critical metals in The nature of deep mantle from the Carnmenellis biotite granite, Afar plume picrites

Cornwall, UK F.M. STUART*1, N.W. ROGERS2, I. PARKINSON2, M. *1 1 1 B.S. SIMONS , J.C.Ø. ANDERSEN , R.K. SHAIL DAVIES2 1 Camborne School of Mines, University of Exeter, 1 Isotope Geosciences Unit, SUERC, East Kilbride G75 0QF Tremough Campus, Penryn, TR10 9EZ. (*[email protected]) (*[email protected]) 2 Department of Earth & Environmental Sciences, Open University, Milton Keynes MK7 6AA. Modern technological developments rely increasingly on resources that have not been the subject of traditional Most mantle plumes are widely believed to originate in exploration and mineral extraction. Emission reduction and the core-mantle boundary. The earliest basalts erupted by low carbon energy production are particularly strong drivers mantle plumes are typically hotter than those derived from for the rising demand for a number of rare metals. The the convecting upper mantle and offer a window into the term “critical metals” increasingly refer to the metals that composition of the deep mantle. For instance, the earliest are of strategic significance for technological development, picrites erupted by the Iceland plume are strongly enriched 3 4 and where the supplies are considered to be significantly at in primordial He ( He/ He ~ 50 Ra), indicating an origin in a risk. This group includes beryllium (Be), gallium (Ga), mantle reservoir that has been isolated from convection for germanium (Ge), tungsten (W), bismuth (Bi), indium (In), most of Earth history. These basalts have, however, a range tin (Sn), antimony (Sb) and the rare earth elements (REE), in radiogenic isotope and incompatible trace element ratios which are particularly significant for components in wind that overlap MORB and cannot simply be reconciled with turbines, photovoltaic cells and nuclear power stations. pristine primordial mantle dominating the plume head. Many critical metals are concentrated in polymetallic In an attempt to provide further constraints on the mineral deposits related to granitic igneous provinces, such source of plumes we have analysed the He-Sr-Nd-Pb as the Variscan intrusions of SW England and Germany. isotopic composition of the earliest basalts from the ~30 Ma However, the geochemical behaviour of the metals in Ethiopian flood basalt province. Picrites from the Dilb igneous systems remains poorly constrained. The lack of section and characterized by high Fe and Ti contents for geochemical knowledge leads to poor understanding of the MgO = 14-15% that implies that the parent magma was concentration mechanisms within the crust, and ultimately derived from a high temperature small melt fraction, most to poor models for their igneous fractionation and probably from the Afar plume head. The picrites are subsequent magmatic-hydrothermal mineralisation. characterized by a narrow range of 87Sr/86Sr (0.70396– This study investigates critical metals within a carefully 0.70412) and 206Pb/204Pb (18.82-19.01), and 3He/4He of selected sample of the Carnmenellis granite (from Holman’s olivine phenocrysts that never exceed 21 Ra. These test mine near Troon, Camborne). The granite was selected observations imply that the Afar plume was sourced in a as an example of the dominant type of coarse-grained discrete mantle reservoir that is less degassed and more porphyritic biotite granite in Cornwall, partly because of the enriched in incompatible elements than the convecting the unweathered and unaltered mineral assemblage, and upper mantle. By contrast, the source region is more partly because the granite in this location has not degassed than the mantle of the proto-Iceland plume and experienced mineralisation. appears to be significantly more homogeneous. This Whole rock geochemical data indicate that Be, Ga, Ge, suggests that the largest mantle plumes are not initiated in a In, Sn, W and Bi are present in higher concentrations than single deep mantle domain with the same depletion history, average continental crust. Sn and Bi show a 5 times and they do not mix with convecting mantle to the same enrichment compared to expected values in crustal rocks extent. with averages of 12.4 and 0.27 ppm respectively. Ge and In show a 2 to 3 times enrichment, with average values of 3.26 and 0.17 ppm whereas Ga shows a 1.5 times enrichment with an average of 24.5 ppm. The future objectives of the study are to better constrain the concentrations of the critical metals in the different types of granite in SW England, and to establish the partition coefficients between the granitic source magma and their constituent minerals. This information will be used to assess the mechanisms of metal concentration within the host granites, and the significance of the individual granite types as critical metal sources for the magmatic- hydrothermal mineralisation systems.

77 VMSG 2013 – Poster Presentation Abstracts

Recognising mush disaggregation in Loading, compaction and injection: basaltic systems: The distribution of Investigating ground deformation olivine compositions in Icelandic on Mt Etna's Northeast Crater basalts and picrites Flowfield A.R. THOMSON*1, J. MACLENNAN2 A. DAVIES*1 1School of Earth Sciences, University of Bristol, Bristol, 1 Department of Geography, Girton College, University of BS8 1DR, UK. (*[email protected]) Cambridge (*[email protected]) 2Department of Earth Sciences, University of Cambridge, Cambridge, CB2 3EQ. Loading by recent lava flows can strongly influence the siting of flank eruptions by downwarping the surface. This The importance of magmatic mushes in controlling both increases stress at the edge of the flowfield, encouraging the behaviour and compositional evolution of magmas has eruptions. Downwarping can be measured through recently been a topic of widespread interest, espeically in levelling. However, lava compaction also causes volcanic relation to silicic systems. There is also plenty of evidence subsidence. Therefore, downwarping is only confirmed if suggesting that mushes play an important role in the benchmarks close to, but off the flow subside by a similar development of basaltic systems. For instance cumulates are amount to those benchmarks on the flow. Vertical an important feature both in the basal wrecks of basaltic movements recorded on the Northeast Crater flowfield on volcanos and in ophiolitic sequences worldwide. However, Mount Etna between 1975 and 1980 confirmed despite this knowledge there has been a surprising lack of downwarping, which progressively decreased. However, effort to identify the compositional and petrographic there was an abrupt increase in subsidence following the signature of mush zone processes in the eruptive products of 1981 north flank eruption. Here, the ground deformation basaltic volcanos. In this study we demonstrate that a was proportional to the thickness of the total flowfield. number of previously unexplained petrological observations This indicated downward movement associated with north can be understood within the framework of magmatic mush flank dyke injections (and subsequent eruptions) is dissaggregation. controlled by the thickness of the total flowfield, rather than A statistical investigation into the forsterite content of the most recent lava flows (Murray, 1988). Icelandic olivine macrocrysts within individual eruptions, There has been no new lava loading on the Northeast and the relationship to their carrier basaltic liquids was Crater flowfield since 1981. However, in 2008, a dyke was achieved using a large compilation of electron microprobe injected beneath the Northeast Crater flowfield and data. 11 eruptions were examined where glass composition considerable summit subsidence was observed. and more than 60 crystal core analyses were available. This investigation aims to establish if downwarping is Kernel density estimates and cluster modelling identified at continuing, and whether downwarping contributed to the least one statistically significant peak in olivine 2008 dyke injection. If downwarping is not evident, it can distributions. In 10 of the 11 eruptions it is observed that be reasoned that the lack of downwarping contributed to the 90% of olivines are too forsteritic to be in equilibrium with lack of subsequent eruption from the injected dyke. A the erupted melt. From the 11 eruptions, 8 show unimodal further research aim is to establish if abrupt flowfield distributions of macrocryst olivine forsterite content, two subsidence associated with dyke injection is still are bimodal and one is polymodal. In all cases a peak in the proportional to the thickness of the total flowfield. distribution occurs at forsterite contents that are 2-3 mol% The data being used for this investigation is part of an higher than those expected for olivines in equilibrium with ongoing annual survey of ground deformation on Mount the carrier liquid. These observations combined cannot be Etna. Data collected through precise levelling in 2007, explained by simple models of equilibrium or fractional 2008, 2011 and 2012 from a traverse set up in 1975 will be crystallisation. used. (I was involved as a fieldworker in 2012). At the time To account for the observations a three-stage model is of abstract submission, only very minor data analysis has required. In the first stage, fractional crystallisation and been performed. Preliminarily, subsidence is known to be crystal settling generate a mush pile on the floor of a ongoing and to have decreased between 2008 and 2012. It magma chamber. Compositional stratification is present in is thought that the subsidence associated with the dyke this mush, with the olivines at its base being more forsteritic injection is no longer proportional to the thickness of the than those at its top, reflecting the evolution of liquid flowfield, but further analysis is needed to confirm this. compositions during fractional crystallisation. In the second A greater appreciation of the causes of ground stage, diffusion occurs in the mush across two different deformation will improve understanding of eruptive paths. Individual olivine crystals homogenise, removing behaviour. Understanding eruptive behaviour is crucial to internal zonation, whilst larger-scale chemical diffusion minimising hazards, with the aid of hazard mapping, land occurs across the entire mush acting to generate a single use planning, and hazard forecasting. Mount Etna's peak in olivine compositions close to the mean forsterite characteristic slow basaltic flows present little risk to human content of the olivines in the crystal pile. Finally, the mush lives, but as Mount Etna is Sicily's main income source, is disaggregated throughout the chamber interior shortly facilitating tourism and agriculture, flank eruptions can have before eruption takes place. Quantitative models of this a significant economic impact on the local region. process indicate that the observed offset peak in olivine Therefore, the local region would also benefit from compositions can be generated after 42-8000 years of improved understanding of the ground deformation. diffusion in a mush pile, depending on the mush thickness. Murray, JB (1988) J Volcanol Geoth Res, 35, p. 121-139.

78 VMSG 2013 – Poster Presentation Abstracts

Detection and categorization of On the lack of InSAR geyser eruption dynamics: Insights measurements of deformation at from infrasound monitoring at Central American Volcanoes

Yellowstone National Park S.K. EBMEIER*1, J. BIGGS1 AND T.A. MATHER2 P.J. DEMONTE*1, J.B. JOHNSON1, A. QUEZADA-REYES2 1 University of Bristol. (*[email protected]) 2 Univeristy of Oxford. 1 Boise State University.

(*[email protected]) A systematic survey of three years of L-band InSAR 2 New Mexico Institute of Mining and Technology. measurements of the Central American Volcanic Arc shows

a striking lack of magmatic deformation. We make Volcanic phenomena such as volatile bubble bursts, gas measurements at 20 of the 26 historically active volcanoes, jets, eruption plumes and pyroclastic flows are strong none of which were deforming magmatically (2007-2010), emitters of infrasound, low frequency (0.02-20 Hz) elastic although we do measure shallow subsidence associated with air waves. These surface-to-air pressure perturbations can flow deposits or edifice instability at three volcanoes. We be easily detected, making infrasound an invaluable use time series variance to estimate minimum InSAR accompanyment to seismic monitoring. Gaining direct deformation detection rates for Central America (average of visual observations of the infrasound signal source 2.4 cm/yr) and show that the majority (>78%) of mechanisms is difficult at volcanoes. However, geysers at deformation events measured at other volcanic arcs would Yellowstone, which are easily accessible and display a wide have been measurable at the same levels of noise as range of behaviours, provide useful analogues for silicic observed in Central America. We estimate that if magmatic volcanoes. volcano deformation were spread evenly across historically The aims of our study are to acoustically detect and active volcanoes worldwide, there would be <2% characterize the eruption dynamics of individual geysers at probability of none of Central America's 26 volcanoes Yellowstone in order to better understand multi-phase fluid deforming. dynamics in geothermal systems. In addition we are using Central America’s high proportion of basalts to the geysers to test the effectiveness of electronic condenser andesites and relative lack of shallow magma storage may microphones (ECMs) and micro-electro-mechanical- contribute to the low number of observations of deformation systems (MEMS) in the development of low-cost acoustic relative to other parts of the world. Other factors with the sensors for volcano monitoring. potential to inhibit the geodetic expression of magma Between August 9th to 14th, 2011, three arrays of four movement include vertically elongated chamber geometries MEMS were deployed around Lone Star Geyser (LSG) and and high volatile contents. Great Fountain Geyser (GFG) in the Lower Geyser Basin at

Yellowstone. An infrasound array was also deployed at Ebmeier, S.K., Biggs, J. and Mather, T.A. (in revision) On Sawmill Geyser (SMG) for an hour on 16th August 2011. the lack of InSAR measurements of deformation at Data were analyzed for their spectral content, acoustic Central American Volcanoes. Journal of Geophysical energy and waveform characterization. To quantify and Research – Solid Earth. compare the pressure fields generated during explosive Ebmeier, S.K., Biggs, J., Mather, T.A. and Amelung, F. (in phases, video footage shot at the geysers was synced with press) Applicability of InSAR to tropical volcanoes: the coincident acoustic signal recordings. insights from Central America. Geological Society Results show that distinct wave forms, eruption Special Publication, Remote-sensing of volcanoes and durations and inter-eruption periods were detected for the volcanic processes: integrating observation and three geysers. SMG was found to generate periodic modelling infrasound dominated by energy in the 1-40 Hz band; its signal source mechanisms are interpreted as: 1) steam-filled bubble oscillations and 2) subsequent bursting at the free surface resulting in violent steam and water discharge. LSG, whose eruptions are characterized by ~18 m/s jets for around 30 minutes, produces higher frequency infrasound and audio-band signal evolving from 20-60 Hz to 40-85 Hz. This is interpreted as phase transition in LSG’s eruptions from mostly water (low acoustic radiation) to steam (high acoustic radiation). During the final stage of an eruption at GFG on August 11, bi-modal infrasound pulses of up to 0.7 Pa-m were detected. Modelling the pulses as volumetric sound sources, we infer that up to 32 m3 of fluid was ejected. Between October 9th to 21st, 2012, three arrays of eight infrasonic sensors (7 ECMs; 1 MEMS) were deployed at different locations in the Lower Geyser Basin. We are currently applying back azimuth and semblance analysis to the recorded data to spatially and temporally locate multiple geyser sources.

79 VMSG 2013 – Poster Presentation Abstracts

Hydroacoustic, infrasonic and Crustal deformation between seismic monitoring of the submarine volcanic segments of the Askja and eruptive activity and subaerial Kverkfjöll central volcanoes, plume generation at South Sarigan, Northern Iceland May 2010 R. GREEN*1, R.S. WHITE 1 T. GREENFIELD 1 J. 1 2 1 *1 2 3 4, TARASEWICZ , H. SOOSALU , J. KEY D.N. GREEN , L.G. EVERS , D. FEE , R.S. MATOZA M. SNELLEN5, P. SMETS2, D. SIMONS5 1 Bullard Labs, Dept of Earth Sciences, Cambridge. 2 Geological Survey of Estonia, Tallin, Estonia. 1 AWE Blacknest, Reading, UK.

(*[email protected]) Seismicity within Iceland clusters spatially mainly 2 KNMI, De Bilt, The Netherlands. within extensional volcanic systems and is often associated 3 Geophysical Institute, University of Alaska, Fairbanks, with active volcanic centres and geothermal systems. USA. However in the Northern Volcanic Zone, unusually intense 4 Institute of Geophysics and Planetary Physics, Scripps upper crustal seismicity is observed in a region between the Institution of Oceanography, University of California, fissure swarms of the Askja and Kverkfjöll volcanic San Diago, USA. systems 3 Acoustic Remote Sensing Group, Faculty of Aerospace This seismicity is persistent through time, and Engineering, Delft University of Technology, The episodically we observe swarms of micro-seismic events Netherlands. locating along linear arrays, believed to be faults. Data

presented here from a dense University of Cambridge Explosive submarine volcanic processes are poorly seismometer network provides evidence of sets of parallel understood, due to the difficulties associated with both north-easterly striking near vertical faults, with left lateral direct observation and continuous monitoring. In this study strike slip motion. Manual refinement and relative hydroacoustic, infrasound, and seismic signals recorded relocation techniques enable the micro-seismicity to be well during the May 2010 submarine eruption of South Sarigan located along a narrow vertical plane striking parallel to the seamount, Marianas Arc, are used to construct a detailed direction of the earthquake slip vectors. event chronology. The signals were recorded on stations of The continuous strike slip motion along these multiple the International Monitoring System, which is a component faults would result in the collective rotation of the faults and of the verification measures for the Comprehensive the crustal blocks between them. This is known as the Nuclear-Test-Ban Treaty. Numerical hydroacoustic and “bookshelf” mechanism of accommodating crustal infrasound propagation modelling confirms that viable extension (Mandl, 1987). propagation paths from the source to receivers exist, and The tectonic deformation probably partitions as it does provides traveltimes allowing signals recorded on the in these areas because the spreading direction is oblique to different technologies to be associated. The eruption the trend of the volcanic rift. There are few fissures or occurred in three stages, separated by three-hour periods of magmatic surface features in the area (Hjartardóttir, 2009) quiescence. 1) A 46 hour period during which broadband with which to correlate the seismicity, probably because it is impulsive hydroacoustic signals were generated in clusters frequently resurfaced by volcanic flows. It is possible that lasting between 4 and 15 minutes. 85% of the 7606 high stresses in the region are as a result of its position identified events could be classified into 8 groups based on between volcanic segments within which the main their waveform similarity. The time interval between extension and magma input occurs. clusters decreased steadily from 80 to 25 minutes during this period. 2) A five-hour period of 10Hz hydroacoustic Mandl, G., (1987) Tectonic deformation by rotating parallel tremor, interspersed with large-amplitude, broadband faults: the “bookshelf” mechanism, Tectonophysics, signals. Associated infrasound signals were also recorded at 141, 277-316. this time. 3) An hour-long period of transient broadband Hjartardóttir, A., (2009) The fissure swarm of the Askja events culminating in two large-amplitude hydroacoustic volcanic system along the divergent plate boundary of N events and one broadband infrasound signal. A speculative Iceland, Bulletin of Volcanology, 141, 277-316. interpretation, consistent with the data, suggests that during phase (1) transitions between endogenous dome growth and phreatomagmatic explosions occurred with the magma ascent rate accelerating throughout the period; during phase (2) continuous venting of fragmented magma occurred, and was powerful enough to breach the sea surface. During the climactic phase (3) discrete powerful explosions occured, and sufficient seawater was vaporised to produce the contemporaneous 12km altitude steam plume.

80 VMSG 2013 – Poster Presentation Abstracts

Local earthquake tomographic Large-scale ground deformation at imaging of a magma chamber Uturuncu volcano: Evidence for beneath Askja Volcano, Iceland magma rise from the Altiplano-

T. GREENFIELD*1, R. GREEN1, J. KEY 1, H.R. MARTENS Puna Magma Body 1 1 1 , M.A. MITCHELL , R.S. WHITE *1 1 1 J.M. HICKEY , J. GOTTSMANN & R. DEL POTRO 1 Bullard Laboratories, University of Cambridge. 1 School of Earth Sciences, University of Bristol, Wills (*[email protected]) Memorial Building, Queens Road, Bristol, BS8 1RJ,

UK (*[email protected]) We have used a tomographic travel time inversion to map a pronounced low velocity anomaly interpreted as a This study focuses on the driving mechanism behind a magma chamber ~ 7 km below the caldera of the Askja 70 km wide region of ground uplift centered on Uturuncu Central Volcano in Iceland. We have operated a high volcano, in the Altiplano-Puna region of southern Bolivia. quality seismic network of 25-30 broad-band seismometers We use Finite Element Analysis to test first-order around the Askja Volcano in the Northern Volcanic Zone parameters that constrain a viable model for the observed since 2006. Using a subset of ~1100 well constrained maximum line of sight uplift rate of 1 – 2 cm/yr between earthquakes distributed across the region, P and S-wave 1992 and 2006. Stresses from pressure sources with finite arrival times have been used to constrain a 1D velocity geometries are solved numerically using COMSOL model of the Askja region using the program VELEST Multiphysics, accounting for both homogeneous and (Kissling et al 1994). The arrival time picks were then input heterogeneous mechanical rock properties in elastic and into a finite difference tomographic inversion program viscoelastic rheologies. To constrain crustal heterogeneity (Roecker et al 2006) and used to invert for a 3D velocity we invert seismic velocity data which indicates the model beneath Askja. prevalence of a very large low velocity zone at depths of Strong (ΔVp ~ -10%) low velocity anomalies are approximately 17 km below the surface. Combined with recorded beneath the most recent caldera within the central other geophysical observations this is deduced to represent volcano and beneath the plain to the west of the regional Altiplano-Puna Magma Body (APMB). We Herðubreiðartögl. These low velocity anomalies are both induce a viscoelastic crustal rheology using the standard interpreted as large magma accumulation bodies. Beneath linear solid model to account for monotonic time-dependent the strong low velocity anomalies within the mid crust, deformation and a crust with an anomalously high heat flux poorly resolved low velocity regions extend sub-vertically and thus inelastic conditions. Investigating crustal into lower crust and are interpreted as melt channels linking heterogeneity alongside homogeneity highlights the the magma body beneath the volcano with melt ponding in significant effect of a mechanically weak source-depth the lower crust or at the Moho. Synthetic model recovery layer. This alters surface deformation patterns by absorbing tests show that the shape of the two large low velocity more of the subsurface displacement, thereby acting as a anomalies are well resolved though the magnitude of the buffering mechanism. As elastic models are unrealistic in velocity anomaly could be underestimated. Additional work this scenario and only account for the spatial component of using travel time delays and S-wave attenuation from the observed uplift, their results are used only to guide the regional and teleseismic arrivals will add further constraints source parameters tested in the viscoelastic models. We to the size and magnitude of the low velocity bodies. then demonstrate a range of possible causative source

geometries but reject spherical and oblate shapes on the Kissling, E., Ellsworth, W. L., Eberhart-phillips, D. and grounds of their depth below the APMB and likely Kradolfer, U. (1994) Initial reference models in local unsustainable pressurisation given the expected crustal earthquake tomography, Journal of geophysical mechanics. A prolate shape protruding from the APMB is Reserach 99, 19,635-19,646. thus favoured. Our final preferred model suggests that Roecker, S., Thurber, C., Roberts, K. and Powell, L. (2006) pressurisation of a magma source extending upward from Redefining the image of the San Andreas Fault near the APMB is causing the observed surface uplift and alludes Parkfield, California using a finite difference travel time to a continued increase in this pressure to explain both the computation technique Tectonophysics 426, 189-205. spatial and temporal patterns. We also demonstrate how a pressure-time function may play a first order role in explaining the temporal deformation pattern.

81 VMSG 2013 – Poster Presentation Abstracts

A comparison of seismically imaged Anatomy of the onset of the current hydrothermal vents with field and repose period at Volcán de Colima laboratory analogues during July 2011

M. HOGGETT1 N. SCHOFIELD2 S.M. JONES2 O. LAMB*1, N. VARLEY2, T. MATHER 1, D. PYLE1 1Geography, Earth and Environmental Sciences Dept., 1 Department of Earth Sciences, University of Oxford University of Birmingham. 2 Facultad de Ciencias, Universidad de Colima. (*[email protected]) (*[email protected]) 2, Geography, Earth and Environmental Sciences Dept., University of Birmingham. After nearly 13 years of continuous activity which included multiple periods of lava-dome extrusion and Intrusion of igneous sills into a sedimentary basin can explosive activity, Volcán de Colima (VdC) in Mexico cause thermal maturation of organic matter and the ceased erupting in July 2011. Historical activity at VdC has generation of significant quantities of greenhouse gases - been dominated by two century-long cycles, 1814-1913 and methane and carbon dioxide. At the same time, pressure can 1913-present, with the transition between these cycles build to the point of rupturing the overlying strata to form a marked by a major eruption in 1913, which occurred after a hydrothermal vent, causing an explosive eruption of the period of quiescence (Luhr and Carmichael, 1980). We have gases to the ocean and atmosphere. used a suite of statistical tools (including detrended Such sudden releases of greenhouse gases hold the fluctuation analysis and spectral analysis) to analyse the 13 potential to cause rapid global climate change. As an months of continuous volcano-seismic data collected in the example, methane generated next to North Atlantic Igneous period up to and including the beginning of the repose Province sills has been postulated to be responsible for the period. These statistical techniques will be used to Paleocene-Eocene Thermal Maximum. However, both investigate whether there are any detectable changes in the methane and carbon dioxide have finite residence times in characteristics of seismic timeseries which may give clues the atmosphere. If these gases were delivered to the to the process or processes that may have led to the atmosphere slowly, they would be removed by natural cessation in activity. These statistical techniques have processes before they could significantly affect climate. previously been shown to work well when analysing Hence, to draw any conclusions as to the importance of sill- fluctuations in the behaviour of both VdC (e.g. Varley et al., vent complexes in causing climate change, we must know (2006), Lachowycz et al., (2013)) and Soufriѐre Hills, the flux of these gasses up the conduit. Little work has been Montserrat (e.g. Nicholson et al., (2013). The aim of this carried out to address this issue. work is to improve our recognition and understanding of the We present brand new images of hydrothermal vents nature of eruptive pauses during long-lived dome-forming made by running spectral decomposition on a high eruptions. resolution 3D seismic dataset from the Bass Basin in southern Australia. This technique has allowed us to image Lachowycz, S. et al., 2013. Long-range correlations the vents and their conduits to a much higher level of detail identified in time-series of volcanic seismicity during than ever before. A comparison of several of these newly dome-forming eruptions. (In preparation). imaged vents is made with field studies on the morphology Luhr, J.F., Carmichael, I.S.E., 1980. The Colima Volcanic of supra-sill hydrothermal vents and kimberlite pipes, and Complex, Mexico: Part I. Post-caldera Andesites from with laboratory experiments on diatremes. The vent Volcán Colima. Contrib. Mineral. Petrol. 71, 343-372. morphologies are used to place bounds on the likely flux of Nicholson, E. et al., 2013, Timeseries analysis reveals gases through the vent, and also on the duration of timescales of cyclical degassing at Soufriѐre Hills explosive activity, in order to shed light on their importance Volcano, Montserrat, Earth and Planetary Science in causing rapid global climate change. Letters (submitted). Varley, N. et al., 2006. Applying statistical analysis to understanding the dynamics of volcanic explosions. From Mader, H. M., et al., (eds) Statistics in Volcanology. Special Publications of IAVCEI, 1, 57–76. Geological Society, London

82 VMSG 2013 – Poster Presentation Abstracts

Modes of volcano growth and Sill geometries in 3D seismic data: linkages to sub-volcanic intrusions Implications for sill emplacement

determined using seismic reflection B. MANTON *1, J.A. CARTWRIGHT 2,1 data from the Ceduna Sub-basin 1 School of Earth and Ocean Sciences, Cardiff University, (offshore S Australia) U.K. (*[email protected]) 2 Department of Earth Sciences, Oxford University, U.K. C. MAGEE*1, E. HUNT-STEWART1, C.A.L. JACKSON1 1 Department of Earth Science and Engineering, Imperial 3D seismic datasets are used to map Palaeogene age College, Prince Consort Road, London, SW7 2BP, sills that intrude Mesozoic sediments, in two regions along England, UK. (*[email protected]) the European Atlantic Margin: the NE termination of the Rockall Trough; and between the More and Voring Basins. Temporal and spatial changes in volcano morphology The sills were emplaced at variable stratigraphic levels, into and internal architecture can influence eruption style and basins dominated by mudstones. location. However, the external and internal characteristics Sills that are emplaced at depths in the range of 1.5 - 4 of volcanoes and their relationship to the sub-volcanic km propagate concordantly, before transgressing at intrusive networks are often difficult to visualise in 3D approximately 45°, often asymmetrically so that the sill is owing to outcrop limitations. We use high-quality 2D transgressive along only along part of its margin. Sills seismic reflection data from the Ceduna Sub-basin, offshore emplaced at shallower depths (0.2-1.5 km), into South Australia to quantitatively analyse 48, pristinely- homogenous fine-grained sediments are predominantly preserved, continental basaltic shield volcanoes, and a transgressive, forming ‘bowl-shaped’ geometries. Sills genetically-related, upper crustal, sill-complex plumbing emplaced in the near-surface (<0.3 km) have lava-like system (c. 42 Ma). Detailed seismic mapping has allowed morphologies. the 3D geometry of each edifice to be reconstructed and the Variations in sill geometry correlate to changes in host internal seismic facies to be studied. The volcanoes have rock lithification state, and its composition. Concordant sills central summits 0.05–0.76 km high, basal diameters of at greater depths indicate fractures following bedding planes 1.80–18.89 km, average flank dips of <12° and range in in well lithified rock. Sill transgression at such depths is volume from 0.12–66.31 km3. Intra-volcano parallel seismic primarily caused by forced folding at the seafloor, causing reflections are interpreted to represent temporally separate stress rotation in the host rock. eruptions originating from a central vent, and suggest that Continuous transgression at shallower levels is shield volcano growth typically occurred by a proportional indicative that sill geometry is less affected by bedding increase in summit height and basal diameter. As the shield planes but more affected by continuous changes in the host volcanoes often overlie lateral sill tips, we suggest that the rock elasticity. Sills at the shallowest levels have intermittent eruption phases correspond to the emplacement morphologies which indicate the host deformed by ductile of incremental magma pulses within the laterally extensive flow rather than fracturing during emplacement. The host is sill-complex. Our observations indicate that the volcanoes interpreted to have been unconsolidated for that to be are not fed by an underlying, centralised magma chamber. possible. Furthermore, several studies have shown that extensive sill- Sills are also observed to propagate along fault planes complexes accommodate a significant proportion of lateral within some harder units. Sills transgressing along multiple magma flow in the upper crust, implying that sill-fed faults can create stepped geometries. These stepped volcanoes may not directly overlie the lower crustal or geometries are observed to limit sill inflation at the sill mantle source of the magma. These results emphasize the margins. applicability of seismic reflection data to quantifying volcano classification and to understanding the evolution of volcanic systems.

83 VMSG 2013 – Poster Presentation Abstracts

Causes of continuous activity at ARGOS: Geophysical study of Arenal volcano, Costa Rica: Alutu

Preliminary results from a volcano- A. NOWACKI*1, J.M. KENDALL1, I. BASTOW2, M. tectonic study WILKS1, J. BIGGS1, A. AYELE3, S. FISSEHA3, E. LEWI3, W. HUTCHISON4, D. PYLE4, F. SAMROCK5, A. *1 1 1 C. MULLER , R. DEL POTRO , J. GOTTSMANN , J. KUVSHINOV5, A. JACKSON5 IGGS1 IEZ 1 ROTTI 2 OTO 3 B , , M. D , M. P , G. S , W. 1 3 School of Earth Sciences, University of Bristol., UK TAYLOR (*[email protected]) 1 Volcanology Research Group, School of Earth Science, 2 Department of Earth Science and Engineering, Imperial Bristol University, UK. (*[email protected]) College, London, UK. 2 OVSICORI-UNA, Costa Rica. 3 Intitute for Geophysics, Space Science and Astronomy, 3 OSIVAM-ICE, Costa Rica. Addis Abab University, Ethiopia. 4 Department of Earth Sciences, University of Oxford, UK. Interactions between tectonic and volcanic systems are 5 Institute of Geophysics, ETH Zurich, Switzerland. not well understood. Here we present the initial results of a joint study combining several dozen UNAVCO’s permanent Alutu is a stratovolcano that lies between the Ziway and GPS stations, a gravimetric campaign and geological field Langano Lakes of the Main Ethiopian Rift. The aim of the results at Arenal volcano which showed more than four multidisciplinary ARGOS (Alutu Research Geophysical decades of relatively low-level continuous effusive activity ObservationS) project is to better understand the magmatic since its reawakening in 1968. Our results indicate that the and hydrothermal plumbing system of the volcano in an magmatic system of Arenal volcano is being built in an effort to assess hazards and geothermal potential. A small active extensional area, which may have promoted the low- (7.3 MW) pilot geothermal plant has been in operation on level yet persistent activity. and off since 1999, but not all wells have been productive. Costa Rica is located in the western part of Caribbean In this project we bring together satellite measurements Plate; the Cocos Plate subducts along the Middle America (InSAR and GPS), seismicity and seismic imaging, Trench (MAT). Low mechanical coupling between the two magnetotellurics, and geologic mapping in an effort to plates has generated a trench-parallel motion up to 10 mm understand the geothermal structure and fluid migration yr-1 toward the North-West, which creates shear stresses patterns. between the MAT and the volcanic arc. Located in the Many of the best geothermal fields are located on sites volcanic arc, Arenal volcano, a basaltic-andesitic prone to magmatic or hydrothermal unrest, and Alutu is no stratovolcano, grew within a comparable short timescale of exception; rapid ground deformation has been remotely a 7ka. The tectonic setting is complex and active observed using InSAR (Biggs et al., 2011). Our hypothesis seismogenic faults surround the Arenal volcanic edifice. is that the ground deformation is caused by repeated After 440 years of dormancy, Arenal erupted in July 1968. injection of magma beneath the Alutu edifice, which in turn The eruptive period lasted until 2010, during which drives a structurally-controlled hydrothermal system. The approximately 0.55 km3 (2 m3 s-1 in 1968 to 0.086 m3 s-1 ARGOS programme is designed to test this hypothesis, between 2000 and 2004; of lava and pyroclasts have been determine the nature of the causative source of ground erupted. displacement, analyse the imposed stresses within the Gravimetric measurements detect an E-W negative reservoir and their influence on coupled fluid flow. It will anomaly with 10 mgal amplitude while the GPS velocities also hopefully reveal why some boreholes are useful shows a centimetric shear strain located within the volcanic sources of geothermally heated water, whilst others are not. arc. These geophysical techniques plus geological field In early 2012 an array of 12 broadband seismometers observations suggest the settlement of the volcanic complex were deployed around the volcano. These data will be used on a pull-apart basin. We propose a hypothesis in which the to help delineate active faults and infer spatial and temporal reported long-lived low effusion rate volcanic activity variations in stress. At the same time, magnetotelluric data would be a consequence of local extensional tectonics and were collected at 50 stations and soil CO2 measurements relatively high heat fluxes typical of active volcanic arcs. were made across the volcano. The magnetotelluric data will be inverted for the 3D conductivity structure beneath

the volcano and the soil CO2 survey will help map out fractures that operate as major gas escape routes. The results will be integrated with existing InSAR and GPS data, and together with detailed geologic mapping will help develop an understanding of the recent volcanic history of Alutu. Early results from the seismic part of the experiment suggest that most earthquakes beneath Alutu are concentrated along rift valley border faults trending NNE– SSW, at shallow depths (less than 5 km), at the east of the

edifice. This correlates with CO2 flux measurements at the surface, suggesting a joint tectonic–hydrothermal driver for seismicity.

84 VMSG 2013 – Poster Presentation Abstracts

Seismic and acoustic indices using Monitoring Cascade volcanoes the registered energies on using InSAR

Tungurahua volcano, Ecuador A.L. PARKER*1, J. BIGGS1, T. WRIGHT2 , Z. LU3 P. PALACIOS1,2, H.M. MADER1, J.M. KENDALL1 1 School of Earth Sciences, University of Bristol. (*[email protected]) 1 School of Earth Science, University of Bristol. 2 School of Earth and Environment, University of Leeds. (*[email protected]) 3 USGS Cascades Volcano Observatory, Vancouver, USA. 2 Geophysical Institute of National Polytechnic School,

Ecuador. Measurements of ground deformation have proven to be a key component of successful volcano monitoring Tungurahua volcano, located at the centre of the Eastern networks. One such technique, Interferometric Synthetic Cordillera of Ecuadorian Andes, reactivated in 1999 Aperture Radar (InSAR), uses the phase shift between generating many episodes of ash falls and pyroclastic flows successive satellite radar images to produce ground up to the present. Stronger episodes have occurred since deformation measurements. A large InSAR dataset has been July 2006, with eruptions ranging VEI 2-3, producing acquired for the Cascade volcanoes in the western USA, but moderate damage to surrounding villages. Since 2006, the snow cover, vegetation, steep topography and atmospheric Geophysical Institute of the National Polytechnic School, in artefacts have limited its application, causing incoherence Quito-Ecuador, have installed a broadband network with and compromising the accuracy of measurements. We are seismic and acoustic sensors, and collected the data in real working to overcome these limitations by using multi- time [1]. temporal InSAR techniques to investigate ground The construction of the seismic and acoustic indices, deformation at Medicine Lake Volcano, CA. based on these main eruptions, might be useful to follow an Levelling surveys throughout the 20th century have on-going crisis, and to forecast the volcanic behaviour in revealed caldera-wide subsidence at Medicine Lake term of minutes to hours. An index is a dimensionless and Volcano. However, the low spatial resolution of relative measure, and its interpretation depends on the measurements mean little is known about the full extent of reference values used in its construction. The average the deformation field. Past InSAR studies have offered little energies released in the stronger eruptions are used here as improvement due to poor coherence across the caldera. To reference values. The interpretation of the volcanic improve upon these studies, we compare the results of three behaviour also depends on the Volcano Acoustic Seismic analysis techniques: stacking, persistent scatterer InSAR Ratio (VASR), the ratio between the acoustic and seismic (StaMPS) and PI-RATE. We find that all methods indicate energies [2]. slow, steady subsidence of the edifice, which we compare to Assuming a stable partitioning of the released energy the results of past geodetic surveys. We use our results as during the eruptions, it is possible to demonstrate that the inputs to inverse models of volume loss at depth. By expected acoustic and seismic indices become equal for coupling these analytical solutions to a thermal model, we both deterministic and stochastic cases. The data analysis of investigate the possibility that present day subsidence is due the stronger eruptions of Tungurahua volcano, and some of to cooling and crystallisation of a sill. its minor crisis periods, appear to be quite consistent with these models. The difference between the indices (seismic index – acoustic index) suggests that seismicity is greater than infrasound prior to a new pulse and that the converse may indicate the end of an eruption. With the normalized VASR (the ratio between the indices) and the spectrograms of the seismic and acoustic signals, we can identify explosions and pyroclastic flows during the eruptions. In addition, the indices show promise as a possible method for generating a forecast in terms of minutes prior to the generation of pyroclastic flows.

[1] Kumagai H., Nakano M., Maeda T., Yepes H., Palacios P., Ruiz M., Arrais S., Vaca M., Molina I., Yamashina T. (2010), Broadband seismic monitoring of active volcanoes using deterministic and stochastic approaches, J. Geophys. Res., 115, B08303, doi: 10.1029/2009JB006889. [2] Johnson J., Aster R. (2005), Relative partitioning of acoustic and seismic energy during Strombolian eruptions, JVGR, 148, 334-354, doi: 10.1016/j.volgeores.2005.05.002.

85 VMSG 2013 – Poster Presentation Abstracts

A photogrammetric feasibility study Decreases in LP seismicity before for DEMs of gulleys in Ecuador the May 2011 eruption of the

J.J. RATNER*1, D.M. PYLE1, T.A. MATHER1 persistently restless Telica 1 Department of Earth Sciences, The University of Oxford Volcano, Nicaragua (*[email protected]) M. RODGERS*1, H. GEIRSSON2, M. WITTER2, D.C.

ROMAN3, P. LAFEMINA2, A. MUÑOZ4, V. TENORIO4 Laguna Cuicocha in Ecuador is a volcanic lake elevated 600 m above and to the west of a town called Cotacachi. 1 University of South Florida, USA Due to new instances of seismicity and aqueous de-gassing (*[email protected]) attributed to renewed volcanic activity, the volcanic hazards 2 The Pennsylvania State University, USA. of the area have recently come under scrutiny. Secondary 3 Carnegie Institution of Washington, Washington D.C., lahars and similar debris flows of mobilized sediment are USA. interpreted as a main concern, based on historic scarp faults 4 Instituto Nicaraguense de Estudios Territoriales and flow channelization that will be likely directed down (INETER), Nicaragua gulleys (called quebradas) towards the populated valley to the east. The occurrence of long-period (LP) events is a This study is an exploration of methods for constructing common short-term seismic precursor to eruptive activity. 3D topographic maps, called Digital Elevation Models However, at persistently restless volcanoes such as Telica (DEMs), of the Laguna’s quebradas. The method of choice Volcano, Nicaragua, potentially important precursory for this study is photogrammetry- a composite DEM built signals can be missed due to the constant high background from correlating recognizable points from a set of digital rate of seismicity. Seismic observations at Telica have photographs. Using a basic point-and-shoot camera, demonstrated the intense background activity over the past hundreds of photographs with overlapping imagery were two decades. Background seismicity at Telica is collected along a section of one quebrada. The method of characterised by LP events with energy predominantly in photo collection was based on previous techniques (James, the 2 Hz and 4 Hz bands. In March 2010 deployment of the et al. 2006) with significant deviations intrinsic to the field TElica Seismic ANd Deformation (TESAND) network was site. Foliage precluded target deployment and photos were completed, consisting of six broadband seismometers, ten collected from the quebrada floor; this method was selected continuous GPS stations and a pressure sensor. In May 2011 as preferable to aerial or more complex methods (involving Telica volcano erupted with a three-week-long series of lasers, targets, LiDAR, etc.) in order to serve as a test for explosions. We analyse 34 months of seismic and geodetic citizen-based photogrammetry in un-idealized locations. data surrounding this eruption in an attempt to identify Similarly, the programs used for photo analysis and DEM precursory changes. The GPS stations show dominantly construction (Photosynth, MethLab, Bundler) were selected regional tectonic deformation, i.e. we do not see clear signs for their availability to the public and relative accessibility of volcanic deformation preceding the eruption. RSAM and to non-experts. spectral analysis of broadband data suggest precursory DEMs are critical inputs for lahar and other flow changes in seismic behaviour at three different time scales. modeling, but must be kept up-to-date in order to provide Eight months before the eruption, we observe a one month accurate scenario guesses. In the event of landscape long swarm of high-frequency (14 Hz) events and a alteration (due to a landslide, slump, human activity, etc.) a concurrent cessation of the LP (2 Hz) events. Eight to ten new DEM needs to be constructed, but the amount of time weeks before the eruption, we observe a sharp decrease in needed for appropriate data collection can be an LP (4 Hz) seismicity. Finally, three to five weeks before the impediment. Should this accessible method of ground-based eruption the high-frequency events return. Over 300,000 photogrammetry prove feasibile for this location, it would seismic events have been detected in the 34 month period have potential applications for involving citizens in future since installation of the first broadband seismometer. We data collection. Utilizing local involvement, DEMs can be located the 100 largest amplitude events per month for a updated much more rapidly than by relying upon scientists nine month period before the May 2011 eruption. These and experts alone, and future methods that utilize events cluster beneath the main vent and in smaller clusters collaborative efforts may prove to be useful for hazard surrounding the edifice. The dense instrumentation at Telica management in many locations across the globe. has allowed us to identify significant decreases in LP activity preceding an explosive eruption. We suggest this Mike R James et al., “Oblique Photogrammetry with Visible decrease may be related to changes in the degassing and Thermal Images of Active Lava Flows,” Bulletin of pathways. Volcanology 69, no. 1 (May 30, 2006): 105–108.

86 VMSG 2013 – Poster Presentation Abstracts

Geodetic data shed light on ongoing Locating the source of volcanic caldera subsidence at Askja, Iceland noise, a picture tells a thousand

H. RYMER*1, E. DE ZEEUW-VAN DALFSEN2 hertz 1 Faculty of Science, The Open University. E. SWANSON *1, M. SCASE 2, D. GREEN3 (*[email protected]) 1 University of Bristol. (*[email protected]) 2 Insitut de Physique du Globe de Paris, Sorbonne Paris Cité, 2 University of Nottingham Paris, France 3 AWE Blacknest

Subsidence within the main caldera of Askja volcano in Volcanic plumes represent a significant hazard both the North of Iceland has been in progress since 1983. Here, near to and at distance from source. Unfortunately, high we present new ground and satellite based deformation data, temporal resolution monitoring, especially in the case of which we interpret together with new and existing micro- more remote systems, is often lacking. Due to their gravity data, to help understand which processes may be turbulent nature, these plumes are a substantial source of responsible for the unrest. From 2003-2007 we observe a sub 10 Hz sound; meaning infrasonic methodology has the net micro-gravity decrease combined with subsidence and potential to fill the monitoring void. Recent studies of from 2007-2009 we observe a net micro-gravity increase volcano infrasound have drawn upon research from the while the subsidence continues. We infer subsidence is aero-acoustics industry, fitting the large scale jet noise caused by a combination of a cooling and contracting spectrum (LSS) to that observed during column generating magma chamber at a divergent plate boundary. Mass eruption events (Matoza et al 2011). However, due to the movements at active volcanoes can be caused by several differences between volcanic plumes and the pure gas jets, processes, including water table/lake level movements, from which the aero-acoustics spectra are created, further hydrothermal activity and magma movements. We suggest laboratory studies are required to investigate the true source that here, magma movement and/or a steam cap in the of the volcanic signals. geothermal system of Askja at depth, are responsible for the In the absence of industrial standard anechoic chambers, observed micro-gravity variations. We rule out the and indeed in terms of the field application of experimental possibility of a shallow intrusion as an explanation for the findings, successful source localisation methods are observed micro-gravity increase and suggest magma paramount. Inverse beamforming, as opposed to the intruded into the residing magma chamber at Askja. commonly used delay and sum methodology, offers a Compressibility of this magma and the magma residing in means to achieve the required spatial resolution of the the magma chamber as well as the compressibility of the generated sound field. surrounding rock may be the reason why this additional In a set of preliminary studies at the University of magma did not create any detectable surface deformation. Nottingham, a 48 microphone array was used to

demonstrate the ability of the inverse method in conditions, de Zeeuw-van Dalfsen, Rymer, H, Sturkell, E, Pedersen, R, less than ideal for acoustic investigations. In addition to the Hooper, A, Sigmundsson, F & Ófeigsson, B. (2012) sound information, a schlieren data set was gathered, Bull Volc (in press). providing details of the plume structure and entrainment Rymer, H., Locke, C.A., Ófeigsson, B. G., Einarsson, P & rate. Findings from these experiments are now being used Sturkell, E. (2010) Terra Nova 22(4): 309-313. to design a thorough laboratory and field study of the

sources of sound from sustained volcanic eruptions

Matoza,R., et al (2009) Geophysical Research Letters Vol, 36 L08303.

87 VMSG 2013 – Poster Presentation Abstracts

Examining Seismic Precursors to Digital mapping of accommodation Eruptions at Volcanoes in structures associated with Extensional Stress Fields Using an emplacement of the Maiden Creek Experimental Approach intrusion, Henry Mountains, Utah R. WALL*1, C.R KILBURN1, P. MEREDITH2 P.I.R. WILSON*1, K.J.W. MCCAFFREY2, R.E. HOLDSWORTH2, J.P. DAVIDSON2, P.J. MURPHY1 1 Aon Benfield UCL Hazard Centre, Dept of Earth Sciences, University College London, WC1E 6BT, UK. 1 School of Geography, Geology and the Environment, (*[email protected]) Kingston University, Penryhn Road, Kingston-upon- 2 Rock & Ice Physics Laboratory, Dept of Earth Sciences, Thames, KT1 2EE (*[email protected]). University College London, WC1E 6BT, UK. 2 Department of Earth Sciences, Durham University, Durham, DH1 3LE. Quantitative analyses of seismic precursors to volcanic eruptions have focussed on volcanoes in compressional High-level sill and laccolith complexes form an background stress fields at subduction zones. We use the important part of volcanic plumbing systems in which results from new laboratory rock-fracture experiments on magma is emplaced as a series of sub-horizontal tabular basalt from Mt Etna, in Sicily, to extend studies to sheets. Most studies of these intrusions concentrate on their volcanoes in extensional stress fields. geometry and internal architecture, while only a few pay Sequences of volcano-tectonic (VT) earthquakes before particular attention to emplacement-related deformation flank eruptions on Etna can develop over months-years, structures in the host rock that record how magma is during most of which cumulative numbers of events accommodated within the crust, i.e. the ‘space problem’. increase exponentially with time. To recreate field This research aims to develop a greater understanding of conditions, we used the fault jog method to generate how igneous intrusive bodies are emplaced and extensional stress within a regional compressional stress accommodated within the shallow crust. field. Two parallel slots, 2 mm wide, were cut at 30° to the Maiden Creek, a satellite intrusion to the Mount Hillers axis in cylindrical samples, 40 mm across and 110 mm long. intrusive complex (Henry Mountains, SW Utah), is a sill- The perpendicular offset between slots was held at 10 mm, like body with a complex elliptical shape with several but the slot overlap was varied from 0 to 10 mm. Water finger-like lobes. Traditional field mapping, outcrop studies saturated samples were deformed under triaxial stress at a and detailed data collection of deformation structures have strain rate of 10-5 s-1, 60 MPa confining pressure and 20 been combined with digital mapping using FieldMove™ MPa pore fluid pressure. Axial strain, volumetric strain and and terrestrial laser scanning (TLS) in order to enable 3D the number of acoustic emissions (AE) and their energy modelling of the intrusive bodies and emplacement-related were measured as proxies for the accumulation of crack host rock deformation. Kinematic and geometrical studies damage within each sample. of emplacement-related structures in the host rocks are Our first results show exponential increases with time in supplemented by microstructural and geochemical studies the cumulative number of AE events (analogues of VT of deformed host rocks, plagioclase feldspar and amphibole events). The trends are consistent with a new theoretical phenocryst populations within the intrusions, and the model for which the exponential trend is characterised by intrusion-host rock contact zone. Fabrics recognised include the energy stored in the atomic structure at absolute both solid-state (associated with accommodating structures) temperatures and confining pressures above zero. The and magmatic features (associated with magma flow). characteristic stored energy can be calculated using rock Detailed outcrop studies across two neighbouring lobes composition, temperature and confining pressure. In our have identified a sub-horizontal shear zone which runs experiments, the exponential trends yield values for the along the top contact of each intrusion. This shear zone characteristic stored energy of 28-36 MJ m-3. These separates low-/moderately-deformed sandstones above from compare well with the calculated values of 32 (+/- 20%) MJ highly deformed sandstones below and between the two m-3. The good agreement suggests that field precursors can lobes, hence acting as a detachment zone. Strain within the be used as a basis for deterministic forecasts of eruptions. highly deformed sandstones is dominated by compressional faults, fractures and fabrics which point to a ‘bull-dozing’ mechanism for lobe emplacement. Fabrics (stretched plagioclase phenocrysts) within the igneous rock, seen on the upper surface of the intrusive lobes directly beneath this shear zone show that the shear zone was contemporaneous with magma emplacement. The shear zone therefore appears to have played a critical role in accommodating magma emplacement.

88 VMSG 2013 – Poster Presentation Abstracts

Comparing predictions of an Dispersal and timing of major integral model with observations of eruptive events at Ischia (Italy), the Eyjafjallajökull 2010 plume insights from distal tephra records

M.J. WOODHOUSE*1, L.J. DOWSON2, J.C. PHILLIPS2 P. ALBERT1, E. TOMLINSON*2,1, L. CIVETTA3, S. WULF4, R. BROWN5, V. SMITH6, G. ORSI3, C. LANE6, M. 1 School of Mathematics, University of Bristol, Bristol, UK. MENZIES1 (*[email protected]) 2 School of Earth Sciences, University of Bristol, Bristol, 1 Department of Earth Sciences, Royal Holloway University UK. of London, Egham, Surrey, TW20 0EX, UK. 2 Department of Geology, Trinity College Dublin, Dublin 2, Volcanic eruption columns inject large quantities of Ireland (*[email protected]) volcanic ash into the atmosphere. The dispersion of ash 3 Instituto Nazionale di Geofisica e Vulcanologia, over large areas results in significant disruption to Osservatorio Vesuviano, Napoli, Italy international transport and infrastructure. The weakly- 4 GFZ German Research Centre for Geosciences, Potsdam, explosive phase of the 2010 eruption of Eyjafjallajökull, Germany Iceland, demonstrated the severe and extensive 5 Department of Earth Sciences, Durham University, consequences of relatively small eruptions to aviation. Durham, DH1 3LE, UK Accurate modelling of the dispersion of ash in the 6 RLAHA, University of Oxford, Oxford, OX1 3OY, UK. atmosphere requires, as input, knowledge of the source conditions at the volcanic vent, in particular the source mass Volcanic activity at Ischia is characterised by flux of material. alternating periods of resurgence, intense volcanic activity It is currently not possible to measure the source mass and quiescence (Orsi et al. 1996). Volcanism at Ischia flux directly. This has led to the development of inversion began prior to 150 ka, with the largest eruption being the 56 methods to estimate the source mass flux based on its ka, caldera-forming Monte Epomeo Green Tuff (MEGT). relationships to the plume height. However, it is difficult to Unravelling eruptive history from proximal deposits can be include all atmospheric controls on the plume ascent, such problematic due to burial, resurgent uplift and erosion. In as wind and varying atmospheric stratification, into such such cases, archives recording distal tephra layers can relationships. provide valuable information about eruptive frequencies and Integral models of volcanic plumes provide an repose periods. alternative approach to estimating source conditions. Here Explosive activity on Ischia has produced several we use an integral model of wind-blown volcanic plumes important distal tephra markers, including the C-18 (60.3 (Woodhouse, Hogg, Phillips & Sparks, 2012) that ka) in the Tyrrhenian Sea (Paterne et al. 1988) and the Y-7 incorporates detailed meteorological data to estimate the (56 ± 4 ka) in the Ionian Sea (Keller et al. 1978; Kraml height of volcanic plumes for specified source conditions, 1997). These tephras were linked to the MEGT and to an and we compare the model predictions to observations of older eruption, the Unita Monte San Angelo (UMSA), by the volcanic plume at Eyjafjallajökull, 2010. the original authors. Refining such correlations is important During the Eyjafjallajökull eruption, plume heights because the Y-7 and C-18 tephras reside close to the marine were recorded by a weather radar, providing a high isotope stage 3/4 climatic transition, which occurs beyond temporal resolution time-series of plume heights. The radar the limit of radiocarbon dating. Consequently, widespread data records variation in the plume height on 24-hour time ash dispersals from Ischia enable the assement of climatic scales. Model predictions can be matched to the leads and lags between different Mediterranean observations during the first week of explosive activity with environmental archives. a near-constant source mass flux, with the varying plume In this contribution, we provide major and trace element height controlled predominately by the atmospheric wind. glass data for Ischia tephras from proximal stratigraphies, In constrast, scaling-law relationships would predict abrupt, whilst distally from Lago Grande di Monticchio (Italy) and order-of-magnitude changes in the source mass flux. other key archives. The tephras span 75-20 ka (USMA to In addition, during the Eyjafjallajökull eruption a web- the St Angelo Tuff) and represent volcanic eruptions camera captured frequent images of the plume. In contrast producing widespread ash dispersals in the Mediterranean to the single-point radar data, web-camera images record region. We define diagnostic geochemical fingerprints for additional information on plume structure and dynamics. key Ischia tephras and provide proximal-distal correlations However, only a portion of the web-camera images provide for a number of important Ischia layers. The correlations are useful data. Here we analyse the web-camera dataset to used to constrain the age and repose times of magmatic determine plume trajectories and plume profiles and activity on Ischia. compare these to predictions from integral models. We show that our integral model is able to describe the wind- Orsi G, Piochi M, Campajola L, D'Onofrio A, Gialanella L, affected trajectory of the plume and the growth of the plume Terrasi F (1996) J. Volcanol. Geotherm. Res. 71, 249– due to the entrainment of ambient air. By matching the 257. model trajectory to the observed trajectory, estimates of the Keller, J., Ryan, W.B.F., Ninkovich, D., Altherr, R., (1978). volcanic source conditions can be made. Geol. Soc. Am. Bull. 89, 591–604. Kraml, M., (1997) Ph.D Thesis Albert-Ludwings- Woodhouse, M.J., A.J. Hogg, J.C. Phillips & R.S.J. Sparks Universitat Freiburg. pp. 216. (2012) Submitted to Journal of Geophysical Research. Paterne, M., Guichard, F., Labeyrie, J., (1988) J. Volcanol. Geoth. Res. 34, 153-172.

89 VMSG 2013 – Poster Presentation Abstracts

Does volcanology work? Evidence A glimpse into the future – earth from the volcanic fatalities record science on trial!

*1 1 2 M.R. AUKER , R.S.J. SPARKS , L. SIEBERT , H.S. R. BRETTON, J. GOTTSMANN, R. CHRISTIE CROSWELLER1, J. EWERT3 The United Nations has played a vital role in improving 1 University of Bristol, UK. (*[email protected]) the governance of natural hazards including volcanic unrest 2 Smithsonian Institution (Ret.), Washington, D.C., USA. and its possible escalation towards a volcanic eruption. The 3 USGS, Vancouver, WA, USA. multi-hazard nature of volcanic unrest including seismicity, ground instability, lahar generation and the release of toxic Demonstrating conclusively the efficacy of proactive gases epitomises the complexity scientists and decision- volcanic disaster risk reduction is of great importance in makers face amid substantial scientific and technological ensuring the continued use of such techniques. To this end, uncertainty during an unrest crisis. we firstly explore basic temporal trends in the volcanic The International Decade of Natural Disaster Reduction fatalities record, and then propose a new measure: the 1990-2000 generated an increased interest in and concern Volcanic Fatalities Index (VFI). The VFI is defined as the for disaster-related issues and in particular proactive risk number of fatalities divided by the product of the number of prevention. World Disaster Conferences in Yokohama recorded volcanic events (fatal and non fatal) and (1994) and Hyogo (2005) and regional conferences, such as population, in a fixed time period. those in Latin-America in Cartagena (1994) and Manizales If vulnerability to volcanic hazards as measured by (2004), have led to action priorities, guidelines and policy fatalities was only controlled by population and numbers of tools. A Global Assessment Report is now issued every two events, then the VFI should be approximately independent years. of time if vulnerability remained unchanged. However, the But little has changed since Kofi Annan, the then VFI declines markedly with time. Values are high and Secretary-General of the UN, said in 1999 “Prevention and th th variable in the 17 and first half of the 18 centuries, likely mitigation are not only more humane than cure: they are due predominantly to poor data quality. The VFI falls also much cheaper… The scientific community understands th sharply over the latter half of the 18 century, with an the importance of the connection between disasters, climate approximately steady decrease observed from 1800 change and policy makers. Prevention policy is too onwards. This reduction in the VFI by about an order of important to be left to governments and international magnitude since 1800 is consistent with a real decrease in agencies alone. That is a mistake. In order to succeed it vulnerability to volcanic hazards. Key explanatory factors must also engage civil society, private sector and the media. include improvements in scientific hazards assessments and We know what has to be done. What is now required is the early warning systems, timely evacuations, better political and social commitment to do it.” preparedness, and greater population awareness. The driver for "renewed political and social A simple postulate is that had no progress been made in commitment" is likely to come from an unexpected source. volcanic disaster risk reduction, the VFI would have Human Rights cases in Strasbourg, France and San Jose, remained at approximately its 1900 value throughout the Costa Rica have clarified the rights to life, private and th 20 century. This value can be used to estimate the fatalities family life, and freedom of information in the context of that might have occurred as a consequence of increased natural hazards. exposure due to exponential population growth. We estimate this number as approximately 85,000, compared to the actual number of 31,728 (the eruptions of Pelée and Nevado del Ruiz excluded). These results provide a numerical indication of the benefits of proactive volcanic risk management, marking an improvement on previous qualitative and anecdotal evidence.

90 VMSG 2013 – Poster Presentation Abstracts

The structure and emplacement of A statistical method for the Rocche Rosse obsidian lava determining the volume of volcanic flow, Aeolian Islands, Italy fall deposits

L. BULLOCK *1, R. GERTISSER1, B. O’DRISCOLL1 R. BURDEN*1, L. CHEN2, J.C. PHILLIPS1 1 School of Physical & Geographical Sciences, Keele 1 School of Earth Sciences, University of Bristol. University, Keele, Staffordshire, ST5 5BG, UK (*[email protected]) (*[email protected]) 2 School of Mathematics, United Kingdom

The emplacement kinematics of silicic lava flows are Volumes of tephra fall deposits are difficult to not well understood, due to a paucity of observations on determine due to the commonly poor preservation of active flows [3]. The measurement of textural and structural proximal and distal areas of the deposit. Typically these features can serve as an important tracer for silicic lava flow volumes are found by extrapolating exponential or power- emplacement and deformation. The Rocche Rosse obsidian law relationships found from isopach maps drawn for the lava flow (1230±40 AD) [1, 2] represents the youngest areas of the deposits that are preserved. However the outpourings of the Monte Pilato pumice cone on the construction of isopach contours is dependent on human northern coast of Lipari (Aeolian Islands, Italy). The flow interpretation of field measurements and can be highly surface is characterised by a brecciated flow top, flow variable, so imposing subjectivity on the final volumes ramps and complex folding. In this study, structural found. measurements on surface features and quantitative textural Here we have investigated the spatial correlation data are coupled with detailed mapping and cross sectional relationships of thickness measurements from fall deposits interpretations of the Rocche Rosse obsidian to gain insight to the vent location to produce a purely statistical method to into its rheological behaviour and emplacement history. objectively determine the volume of a deposit, without the We present a new 1:3,000 scale structural map of the production of isopach maps. Integration of a log linear Rocche Rosse obsidian. Complex folds and refolded folds regression model for thickness measurements with distance (sheath folds) are mapped on a scale of decimeters to tens of from the vent is applied to the field measurements without metres. Planar (primary banding and fold axial planes) and any prior interpretation. The use of an exponential function linear (fold hinges and stretching lineations) structures in this method is based purely on the statistical requirement suggest overall flow-perpendicular foliation and flow- that data needs to be transformed to a normal distribution parallel lineation trends (with localised anomalies, where and is not informed by physical processes. At a fixed structural observations do not conform to the trends). Small- distance from the vent there can be significant variability in scale flow folding on a decimeter scale is extensive, as is the thickness data from a deposit that can lead to large the generation of larger-scale folding. Spherulites are uncertainties in the volumes found, a feature of the deposit apparent, with strain analysis, textural observations and that is lost in the production of isopach maps. To account crystal-size distribution (CSD) measurements suggesting for this variability in the data a Bayesian approach has been multiple populations of subcircular to ellipsoidal spherulites adopted which provides a systematic method for exist. A complex range of spherulite textural fabrics and determining the uncertainty in the volume estimated. shape profiles points to protracted down-temperature Volumes calculated from our method correspond well to spherulite formation that can be linked to specific stages in those previously determined by alternative approaches. The the emplacement history and deformation regime of the lava quantification of uncertainty in field measurements and flow. model error, and the removal of subjectivity incurred by the The dominant foliation and lineation trends are production of isopach maps, suggests the method presented interpreted as a function of flow frontal compression (at here can offer benefits in determining the volumes of fall shallower topographic gradients) and mid-flow constriction deposits. (steeper topographic gradients) occurring during flow emplacement. Initial compression leads to the generation of small scale folding, with increased cooling (leading to crustal thickening) and compression resulting in a second and, possibly, a third generation of larger-scale folding and sheath folding. Variations in structural and textural trends relate to areas of complex deformation, such as at the flow front or flow margins. The detailed textural and structural features documented here provide important constraints on the rheological properties of the Rocche Rosse obsidian, important for understanding the structural kinematics and emplacement mechanisms of this silicic lava flow.

[1] Arrighi, S. et al. (2006) Phys. Earth Planet. Int. 159, 225-233. [2] Clay, P. et al. (2012) Contrib. Mineral. Petrol. DOI 10.1007/s00410-012-0813-x. [3] Tuffen, H. et al. (2012) Geophys. Res. Abs. 14, EGU2012-11451-2, 2012

91 VMSG 2013 – Poster Presentation Abstracts

Ecological impacts of degassing and Advances in the construction of deposition from recent activity at volcanic records from marine Volcán Turrialba, Costa Rica sediment cores: A review and case

B. BURSON*1,2, R. MARTIN1 study (Montserrat, West Indies) 1 Department of Geography, University of Cambridge CB2 3EN M. CASSIDY*1, J. TROFIMOVS2, M.R. PALMER1, W. 2 Department of Environment, Earth and Ecosystems, The SYMONS1 Open University, Milton Keynes, MK7 6AA (*[email protected]) 1 National Oceanography Centre, University of Southampton, European Way, Southampton, SO14 Volcanic degassing releases a variety of volatiles which 3ZH. (*[email protected]) are locally deposited. Biomonitoring has be used to indicate 2 Queensland University of Technology, Brisbane, Australia, the spatial patterns of deposition1, but the extent to which 4000 persistent volcanic degassing pollutes nearby ecosystems has been less well investigated. Since 1996, when the latest This work tests and reviews current techniques used to phase of degassing began at Volcán Turrialba2, there has generate volcanic eruption records from marine sediment been increasing damage to the surrounding vegetation. cores using the volcanic island of Montserrat as a case Using soil pH and element analysis of grasses alongside study. The data is presented using cores sampled both ecological data, it was found that acidification from proximally (8-14 km) and distally (55 km) from south and Turrialba is the component of volcanic degassing that has south west offshore Montserrat. the strongest effect on local ecosystems. Based on these studies we suggest the following Soil pH and ICP-OES analysis of grass (Poa annua) protocol for generating volcanic records from submarine samples were used to identify the spatial distribution of the sediment cores: (1) visual sedimentological logging of deposition of volcanic elements, which was statistically visible tephras, (2) the use of time-efficient, non-destructive assessed using Principle Components Analysis (PCA). Acid and high spatial resolution techniques that are able to detect deposition decreases with distance downwind (west) from and locate potential tephra horizons (e.g., XRF core the volcano. This is accordant with results from Masaya scanning and magnetic susceptibility), (3) sampling of (Nicaragua), where acidifying species such as HCl are targeted horizons for microscope analysis to discriminate rapidly scavenged from the plume and deposited nearby3. between primary and reworked volcanic deposits (this has The concentration of the volcanogenic elements Cd, Co, been achieved here by using specific criteria related to clast Cu, Hg, Ni, Pb and Rb (PC1) in Poa annua is highest morphology, compositional maturity, sorting and several km west of the volcano. These may be deposited sedimentological facies indicators), and (4) dating the after acidifying compounds, and therefore further intervening hemipelagic sediment, by AMS radiocarbon downwind from the volcano. The concentration of the base dating on foraminifera (when younger than 47 ka) and, for cations Ba, Ca and Sr (PC2) in Poa annua is anti-correlated older marine sediment, using oxygen isotope stratigraphy. with soil pH. These are probably being leached from acidic As a result of this procedure, more discrete volcanic soils, which been observed in grasses at volcanoes events have been recognised than previous marine elsewhere1. Acidifying species that are rapidly deposited tephrochronological studies in this region. from the plume may also be responsible for leaching the elements in PC1 from the soil closer to the volcano, producing an apparent centre of deposition several km from the source. These results were correlated with data from a vegetation incidence survey using Canonical Correspondence Analysis (CCA) as well as a tree defoliation index. The diversity of understory flora is much lower at sites exposed to the plume, though some plant species are more tolerant to volcanic degassing. According to CCA, the diversity of flora is best explained by the pH of the soil. Defoliation of trees is positively correlated with acidity. Furthermore, since no elements were found at phytotoxic levels in Poa annua, it is concluded that acid deposition is the most important cause of vegetation impacts from degassing at Turrialba.

Martin, R.S. et al. (2010) Bulletin of Volcanology 72(8), 1009-1020. Martini, F. et al. (2010) Journal of Volcanology and Geothermal Research 198, 416-432. Delmelle, P. et al. Environ Sci Technol 35(7), 1289-1293.

92 VMSG 2013 – Poster Presentation Abstracts

Landslide processes at Montserrat, Interactions between mitigation Lesser Antilles, and their strategies: Implications for the implication for tsunami generation scientific bases of mitigation policy

M. COUSSENS*1, P. TALLING 1, S. WATT1, M. CASSIDY1, S. DAY*1, C. FEARNLEY2 M. PALMER1 1Aon Benfield UCL Hazard Centre, Department of Earth 1 National Oceanography Centre Southampton, European Sciences, University College London Way, Southampton SO14 3ZH (*[email protected]) (*[email protected]) 2 Institute of Geography and Earth Sciences, Aberystwyth University. The ongoing eruption of Soufrière Hills volcano, Montserrat, has involved multiple dome collapses, which Recent events in natural disasters, such as the have produced pyroclastic flows and ultimately led to the malfunctioning of the Japanese tsunami warning system in offshore deposition of >65% of the total erupted material. the 2011 Tohoku tsunami, reveal a need for a systematic The largest collapse in 2003 had a volume of 0.2 km3, and classification of mitigation strategies; an understanding of generated a local tsunami 1m high that was recorded 48 Km the scientific uncertainties that affect the effectiveness of away on the shores of Guadeloupe. Several much larger such strategies; and an understanding of how the different landslide deposits have been detected offshore Montserrat types of strategy within an overall mitigation policy via swath bathymetry and seismic surveys, the largest of interact, often destructively, to reduce the effectiveness of which involved ~20 km3 of material. Although infrequent, overall mitigation policies. This occurs especially where such events may generate regionally significant tsunamis. policies deal with multiple hazards and interactions between However, their potential for tsunami generation is strongly those hazards (“multihazards”) and their impacts dependent on whether these landslides were formed in (“multirisks”). The variety and complexity of volcanic single or multiple stages, and in where the material was hazards means that these issues are particularly important sourced from (i.e. volcanic flank failure versus the for volcanologists. incorporation or secondary failure of seafloor sediment). To We divide mitigation strategies into permanent; provide a better understanding of landslide and tsunami responsive; and anticipatory. Permanent mitigation hazards around this volcanic island, it is important to strategies such as coastal and river flood defences or land constrain landslide magnitude, frequency, and specific use restrictions around volcanoes, are both costly and emplacement processes. The recently collected cores from “brittle” in that when they fail they can actually increase IODP Expedition 340 provide samples of multiple mortality by their influence upon peoples’ expectations and landslide, fallout and turbidite deposits spanning the their actions during disasters. Such strategies therefore development of Montserrat. Here, we describe the current critically depend on the accuracy of the underlying hazard state of knowledge regarding the eruption and mass-wasting assessments. Responsive mitigation strategies such as history of Montserrat, and show how the new core samples tsunami and lahar warning systems rely on capacities to will be used to advance this understanding. We aim to detect and quantify the hazard source events and to transmit understand better the emplacement processes of the largest warnings fast enough to enable at risk populations to decide landslides around Montserrat; to investigate the relative and act effectively. Self-warning and voluntary evacuation frequency, and any episodic behaviour, of the different is also usually a responsive mitigation strategy. Uncertainty mass-wasting processes around Montserrat; and to provide a in the nature and magnitude of the detected hazard source clearer record of the early development of Montserrat by event is often the key scientific obstacle to responsive integrating onshore and offshore data. mitigation; public understanding of both the hazard and the warnings, to enable their decision making, is also a key factor that hazard scientists can address. Anticipatory mitigation strategies use interpretation of precursors to hazard source events and are used widely in mitigation of volcanic hazards. Their critical limitations, due to uncertainties in time, space and magnitude relationships between precursors and hazard events, are perhaps better understood by volcanologists than by other hazard scientists. Understanding the interactions between these different types of mitigation strategy, especially in the multirisk environment of a complex natural disaster, requires models of rapid decision making under high levels of both uncertainty and danger. We propose that the Observation- Orientation-Decision-Action (OODA) loop model (Boyd, 1987) may be a particularly useful model, especially in its emphasis that flexibility counteracts uncertainty.

Boyd, J.R. A Discourse on Winning and Losing [http://dnipogo.org/john-r-boyd/]

93 VMSG 2013 – Poster Presentation Abstracts

Eruption and depositional facies of Bentonised silicic pyroclastic fall the Stob na Doire Ignimbrite deposits at the base of the Member, Glencoe, NW Scotland: Palaeogene Skye Lava Field which Fault-bounded rheomorphic/lava- possess welded ignimbrite like like and eutaxitic ignimbrites fabrics

J. DIETZ*1, D. BROWN1, R. DYMOCK1 S.M. DRAKE*1, A.D. BEARD1 1 School of Geographical and Earth Sciences, University of 1 Department of Earth and Planetary Sciences, Birkbeck Glasgow, Gregory Building, Lilybank Gardens, College, University of London, Malet Street, London, Glasgow, G12 8QQ, UK. WC1E 7HX (*[email protected]) (*[email protected]) Silicic pyroclastic rocks deposited prior to basaltic lava Glencoe, NW Scotland, exposes the roots of a late fields within the British-Irish Palaeogene Igneous Province Silurian-early Devonian (~420-400 Ma) caldera volcano. (BIPIP) are unrecorded. We report on the first such The caldera is dominated by a succession of silicic occurrence from beneath the lowermost Skye Lava Field at pyroclastic rocks, together with intermediate and silicic An Carnach, Strathaird Peninsula, Isle of Skye, NW lavas, and intrusions. The caldera sequence comprises a Scotland. Here contemporaneous basic and silicic eruptions wide range of ignimbrite lithofacies, which represent major are recorded by former silicic ash-fall deposits which explosive eruptions associated with volcano-tectonic contain chlorite mica stacks. The presence of these stacks subsidence and piecemeal caldera collapse. Subsidence was likely indicate basaltic ash settled out in a marine water incremental and occurred along a series of cross-cutting column (Merriman and Peacor 1999). The silicic-ash fall faults (Moore & Kokelaar 1998). We report on a newly- deposits were subsequently altered to K-bentonite by either identified sequence of ignimbrites, previously interpreted as intrusion of a later adjacent tholeiitic sill, or by the weight lavas and attributed to the Bidean nam Bian Andesite of the overlying lava pile. Member (Moore & Kokelaar 1998), and explain their The alteration of the protolith to K-bentonite has eruption and depositional history. We propose the name the resulted in a remarkable eutaxitic like fabric which is ‘Stob na Doire Ignimbrite Member’ for these rocks. defined by a strong planar fabric which has frequently been The Stob na Doire Ignimbrite Member is located on the deflected around heterolithic lapilli. This fabric was flanks of Stob na Doire on the Buachaille Etive Mor massif produced in the cold state since it lacks recognised hot state in eastern Glencoe. Its northernmost exposure is fault- characteristics (Branney and Sparks 1990). In the field the bounded against sandstones and breccias of the Glas Choire K-bentonite strongly resembles a silicic welded ignimbrite. Sandstone Member. The lowermost part of the exposure Classification to K-bentonite was only possible using an comprises ~40 m of crystal- and lithic-rich andesitic-dacitic electron microprobe since the Al and Si peaks were much rheomorphic/lava-like ignimbrites. These ignimbrites higher and lower respectively than those expected in a display a strong flow-fabric/parataxitic texture and folds are silicic welded ignimbrite. locally present. The fabric is near vertical in the vicinity of The ability to distinguish between ‘ancient’ bentonite the fault but progressively shallows up sequence and away and welded ignimbrite in the field is therefore called into from the fault, indicative of active subsidence and ponding question and may have implications for volume during the eruption. The high-grade nature of these considerations of silicic welded ignimbrite in some volcanic ignimbrites records a sustained, low-fountaining, ‘boil-over’ terrains, and the paucity of silicic air-fall deposits in others. type eruption. Branney, M.J. and Sparks, R.S.J. 1990. Fiamme formed The rheomorphic/lava-like ignimbrites pass up into an by diagenesis and burial-compaction in soils and ~100 m thick sequence of andesitic-dacitic ignimbrites subaqueous sediments. Journal of the Geological Society of comprising both eutaxitic welded lapilli-tuffs and non- London. 147. 919-22 welded lapilli-tuffs and breccias, indicative of a change to Merriman, R J. and Peacor, D.R. 1999. Very low- grade more pumiceous Plinian eruptions. The transition is marked metapelites: Mineralogy, microfabrics and measuring by ~5 m of alternating rheomorphic lapilli-tuffs with reaction progress. In: Low grade metamorphism (M Frey distinctive strongly eutaxitic lapilli-tuffs, locally with basal and D Robinson. Blackwell Science Oxford Pp160. vitrophyres. The sequence then passes up in to more typical massive lapilli-tuffs, locally with lithic breccia horizons, and moderately welded eutaxitic zones. These ignimbrites record granular fluid-based pyroclastic density currents, and are indicative of waxing and waning of the eruption due to variations in mass flux.

Moore, I., Kokelaar, P., (1998) Bulletin of the Geological Society of America 110, 1448-1466.

94 VMSG 2013 – Poster Presentation Abstracts

The importance of conduit erosion Modelling disaster risk scenarios at J.B. HANSON*1, A.C. RUST1, M.J. PAVIER1, J.C. La Soufrière, Guadeloupe 1 PHILLIPS *1 2 3 S. JENKINS , R. SPENCE , P. BAXTER , J.C. 1 University of Bristol (*[email protected]) KOMOROWSKI 4, S. BARSOTTI 5, T. ESPOSTI-ONGARO 5, A. NERI 5 Conduit geometry is known to affect flow processes and 1 University of Bristol. (*[email protected]) critical points such as the fragmentation level. 2 Cambridge Architectural Research. Consequently, conduit flow models are becoming 3 University of Cambridge. increasingly sophisticated in terms of conduit shape and 4 Institut de Physique du Globe de Paris. elastic deformation. Conduit erosion (ie. the permanent 5 Istituto Nazionale di Geofisica e Vulcanologia. removal of material) would modify conduit geometry during eruptions and thus may be influential in terms of As part of the CASAVA project, potential consequences eruption dynamics. However, there has been very little of an eruption at La Soufrière volcano, Guadeloupe, have modelling of conduit erosion and conduit erosion and been quantified for the local population and infrastructure conduit fluid dynamic models have yet to be coupled. through development of an impact model. For a given Finite element analysis is a powerful tool to elucidate eruption scenario, and on a 250m grid, the model the behaviour of the wall-rock during both dynamic and incorporates hazard information about areas potentially static loading such as those which occur in volcanic affected by ash fall (vertical loading) and/or pyroclastic systems, and is capable of dealing with inherently non- density currents (peak dynamic pressure, temperature and linear and complex systems. Our initial investigations have duration) sourced from numerical modelling able to focused on the static effect of the conduit over- and under- describe the transient and 3D features of the phenomena. pressures determined by steady 1-D models of Costa et al, This is combined with vulnerability information derived 2009 (ranging from +30MPa to -106 MPa, with respect to from engineering and medical analyses of the exposure and lithostatic). Changing the rheology of the wall rock from response of humans and buildings to these hazards. Model elastic to elastic-plastic, using reasonable rock properties outputs include maps of the numbers and severity of human (Youngs Modulus = 40 GPa, Poissons ratio = 0.25, and casualties and building damage for each given scenario. The Yield Strength =2-20MPa) has a significant effect both on impact model is further coupled with a dynamic casualty conduit displacement and the volume damaged (e.g. 50,000 management model that then tracks the rescue, transport m3). This damage will be particularly important in areas of and treatment of casualties to estimate the impact of the conduit underpressures, as this material will implode into eruption on the emergency services and on casualty the conduit; erosion in damaged overpressured areas numbers with time following the eruption. This allows requires a further mechanism to remove material (e.g. dynamic mapping of human survival in space and time magmatic shear stress or particle collisions). following the eruption scenario and can be combined in GIS The amount of damaged material strongly (orders of with emergency management data to support public magnitude) depends on the initial size of the conduit, the officials responsible for planning for a crisis. To identify yield strength of the material and the applied pressure suitable actions that could be taken to reduce the loss of difference. Lithological variations along the conduit wall lives and infrastructure, the consequences from different (i.e. materials with differing strength properties, e.g. granite disaster risk scenarios can be tested by varying the crisis to schist, as seen at volcanoes such as Ramadas, Argentina) conditions for each model run. For example, by are very important for conduit erosion and thus conduit incorporating short- and long-term mitigation activities (e.g. geometry evolution and potentially fragmentation level partial evacuation, construction of additional road progression. capacity), differing emergency management (e.g. the The FEA work is complemented by field studies at location of triage centres) or simulating alternative disaster Vesuvius volcano, Italy, on the Pollena, Avellino and conditions (e.g. reduced rescuing capacity because of ashy Pompeii deposits. Lithics of various lithologies (notably conditions). The models are deliberately generic in nature carbonates and older volcanics) indicate the occurrence of and could be applied to any volcano, providing input hazard conduit erosion along a large portion of the conduit scenarios and appropriate exposure and vulnerability data (estimated to be ~5 km long, with a division between the are available. hosting rocks at around 1800m below the summit –

Macedonio et al, 1994). Detailed size and shape analysis of the lithic material suggests there is a correlation with the previous fabric of the wall rock material, rather than a distinction based on erosive mechanism.

Costa, A., Sparks, R.S.J., Macedonio, G., and Melnik, O. (2009) EPSL 288, 455-462. Macedonio, G., Dobran, F., and Neri, A. (1994) EPSL 121, 137-152.

95 VMSG 2013 – Poster Presentation Abstracts

Revised Estimates for the Volume of Stratigraphy and eruption history the Minoan Eruption of peralkaline welded ignimbrites,

E.N. JOHNSTON*1, R.S.J SPARKS1, J.C PHILLIPS 1 Island of Pantelleria, Italy 1 School of Earth Sciences, University of Bristol, Wills N. JORDAN*1, M. BRANNEY1, M. NORRY1 Memorial Building, Queens Road, Bristol, BS8 1RJ, 1 University of Leicester. (*[email protected]) UK. (*[email protected])

A revised volcanic stratigraphy is presented for the Assessments of erupted volumes are prone to a number ignimbrites of Pantelleria, a peralkaline caldera volcano of potentially significant sources of error or omission. Large situated in the submerged continental rift between Africa caldera-forming eruptions are associated with three main and Sicily. The volcano has been active for ≥325 ka types of deposit: intracaldera ignimbrite fill; outflow (Mahood & Hildreth, 1986), producing at least six major ignimbrite sheets; and tephra fall-out. Volumes of all three ignimbrites from large central eruptions, which appear to components are rarely estimated which often leads to have alternated with numerous minor pumice falls and lavas uncertainties in total volume estimations. The Bronze Age from scattered local centres. The main ignimbrites can be (‘Minoan’) eruption of Santorini is a classic example of this. traced along superb coastal exposures and have been logged Four Minoan eruptive phases have been recognised on in detail. Eruption-units have been defined by the position Santorini. Interpretations of these phases are straightforward of palaeosols and a type section designated. Lithic breccias and non-controversial. Difficulties, however, arise regarding and pumice fall deposits associated with these major the phase 3 deposits; one enigma is how these cold, ignimbrites are interpreted as part of the same eruption pyroclastic flows could have been erupted over the steep overcoming correlation problems encountered by previous caldera cliff walls but were deposited on shallow slopes workers (cf Mahood & Hildreth, 1986). (typically 15° but up to 30°). We propose that the caldera The ignimbrites are 2 to >20 m thick, welded to was completely infilled by pyroclastic material during rheomorphic and cover most of the island, recording phases 2 and 3. Only when the caldera was filled was it devastating, radial, high-temperature density currents. Five possible for the phase 3 deposits to overflow the caldera rim of the six major ignimbrites contain lithic breccias, which and produce outflow sheets. Initial calculations suggest an have commonly been interpreted as recording caldera infill volume in excess of 23 km3. We suggest this material collapse events, but the details of individual calderas are not has been down-faulted during caldera collapse. Geophysical clear. The ignimbrites were erupted between 175 and 50 ka and seismic data are consistent with a large volume of suggesting that the early history of the island (325 to down-faulted intracaldera fill, both of which indicate 175 ka) differs from later stages in that only local pumice several hundred metres of low density deposits on and lava-producing eruptions have occurred. This means Santorinis caldera floor. This model has implications for that the amount of erupted magma increased in the later estimates of the size of the eruption. Our initial results, in stage as the ignimbrites represent eruptions of many times addition to the most recent published estimate of 60 km3 the volume of the local centres. DRE, suggests the volume of the eruption should be raised Distal peralkaline tephras have been found around the to 72-93 km3 DRE, making it the largest known explosive Mediterranean as far away as ~1200 km. With only this Holocene eruption. volcano erupting peralkaline compositions, it suggests that eruptions from Pantelleria have had a substantial impact on their environment. We infer that there were few Plinian events on the island, and that the distal tephras may be co- ignimbrite ashfall deposits.

Mahood, G.A., Hildreth, W., (1986) Bulletin of Volcanology 48, 143-172.

96 VMSG 2013 – Poster Presentation Abstracts

Drilling into a super-eruption Glacial modulation of eruptive caldera? Initial report of the activity at Volcán Sollipulli, Chile

proximal rhyolites revealed by the S.M. LACHOWYCZ*1, D.M. PYLE1, T.A. MATHER1, K. Snake River deep drill hole, Idaho MEE2, J.A. NARANJO3 1 Department of Earth Sciences, University of Oxford, UK. T. KNOTT*1, M. BRANNEY1, M. REICHOW1, M. (*[email protected]) MCCURRY2 AND THE HOTSPOT TEAM 2 British Geological Survey, Keyworth, Nottingham, UK. 1 Dept. of Geology, University of Leicester, University 3 SERNAGEOMIN, Santiago, Chile Road, Leicester, UK. (*[email protected]) 2 Dept. of Geosciences, Idaho State University, Pocatello, There is growing evidence that changes in ice cover on USA. stratovolcanoes may influence the timing and rate (e.g., Watt et al. [2011]) as well as the style (e.g., Mee et al. Project HOTSPOT seeks to understand voluminous [2009]) of eruptive activity. These effects could potentially bimodal volcanism and magma generation in the Snake be enhanced at those volcanoes with ice-filled large craters River-Yellowstone LIP, USA. A 1.9 km-deep drill hole in or calderas, which also pose particular hazards in the event the Snake River Plain, southern Idaho has cored the mid- of renewed activity and with changing climate. One such Miocene rhyolitic succession marginal to the putative Twin edifice is Volcán Sollipulli in Chile, located at ~39°S Falls explosive centre and provides a unique window into between Llaima and Villarrica in the Southern Andean otherwise concealed proximal deposits. Four rhyolitic Volcanic Zone. This little-studied volcano has a ~4 km wide eruption-units occur separated by basalt lavas, palaeosols summit caldera containing ~6 km3 of ice, which is believed and volcaniclastic sediments. Whole-rock, glass, and to have formed without any explosive eruption [Gilbert et mineral chemical data (XRF, EMP) from the top and base al., 1996]. of each facilitate correlation with units exposed distally, and In this study, we examine how ice cover and intra- aid volume calculations of some of the most catastrophic, caldera ice has influenced the style of late Quaternary hot super-eruptions in Earth history. Rhyolite 1, the lowest eruptive activity at this volcano, and possibly the timing of unit, is >1322.78 m thick and extends beyond the base of caldera formation. We present preliminary results from the well. Its pyroclastic origin is indicated by a eutaxitic study of the field relationships, textures, and geochemistry foliation with abundant obsidian chips (2–5 mm). Its of the eruption stratigraphy exposed around the caldera thickness suggests ponding in the margin of a caldera. wall, as well as some more distal eruption deposits. A wide However lithic mesobreccias, as characterise caldera fills range of volcanic ‘lithofacies’ are observed, probably elsewhere, are not seen. Lake sediments (18 m) separate it reflecting varying degrees of interaction between glacial from overlying Rhyolite 2 (159.41 m thick), which has a meltwater and the erupting lava, in addition to the extent of non-brecciated glassy base, a lithoidal centre also with 2–5 alteration and remobilisation of these eruption products. mm obsidian chips and an upper glassy rheomorphic These ‘lithofacies’ appear to range between various end- autobreccia. It is probably a proximal outflow correlative of members, which we use as the basis of a novel, simple an ignimbrite exposed further south. Rhyolite 3 (8.84 m classification scheme that relates to the inferred formation thick) is glassy, with upper and lower autobreccias 5.7 m processes. and 1.5 m thick. It is separated from Rhyolite 2 by a 2.7 m- From these eruption deposit sequences, we also infer the thick zone of glass clasts in clay, which may represent an palaeo-ice depth through time. Indications of a short time altered zone within a single eruption-unit. Laminated lake period between the latest pre-caldera and first post-caldera sediments 64 m thick, basalt lavas, 67 m thick, 23 m units constrain caldera formation to during or shortly after a sediments, and 30.5 m basalt lava with an upper palaeosol period of deglaciation. This is consistent with the are succeeded by Rhyolite 4 (127.1 m thick). This has a occurrence at nearby Llaima and Villarrica of assumed glassy basal autobreccia (4.5 m), well-developed flow caldera-forming, ignimbrite-forming eruptions during banding and no visible pyroclasts, and may be part of the deglaciation following the Last Glacial Maximum [Lohmar 6.3 Ma, <200 m thick Shoshone rhyolite lava [1]. et al., 2005], and contrasts with recent modelling of the [1] Armstrong et al., (1975) American journal of science potential influence of ice loading on caldera formation 275, 225-251 [Geyer & Bindeman, 2011].

Geyer, A., & I. Bindeman (2011) J. Volc. Geotherm. Res. 202, 127–142. Gilbert, J.S., et al. (1996) Bull. Volc. 58, 67–83. Lohmar, S., et al. (2005) 6th International Symposium on Andean Geodynamics Extended Abstracts, 442–445. Mee, K., et al. (2009) Bull. Volc. 68, 363–376. Watt, S.F.L., et al. (2011) Quat. Int., 246, 324–343.

97 VMSG 2013 – Poster Presentation Abstracts

Development of a database of Lithofacies architecture of the volcanic ash layers from ocean Stallachan Dubha Ignimbrite drilling cores as a record of global Member, Ardnamurchan, NW explosive volcanism Scotland: valley-filling ignimbrites S.H. MAHONY*1, R.S.J. SPARKS1, N.H. BARNARD3 and the incursion of pyroclastic 1 University of Bristol. (*[email protected]) density currents into a lake

*1 1 1, 2 C. MCLEAN , J. BUCHANAN , P. REYNOLDS , P. Ocean drilling is a largely untapped source with the 1, 3 1 1 1 NICHOLLS , R. DYMOCK , C. PATMORE , D. BROWN potential to generate a more complete record of global volcanism through time. Creation of a global dataset of ash 1 School of Geographical and Earth Sciences, University of layers through time is the initial aim of this work, these Glasgow, Gregory Building, Lilybank Gardens, layers will then be translated into volcanic eruptions of Glasgow, G12 8QQ, UK. varying magnitude, essentially forming a global time series (*[email protected]) of explosive volcanic eruptions. This will then be used to 2 Department of Earth Sciences, Durham University, examine magnitude-frequency relationships, look to see Science Labs, Durham, DH1 3LE (present address) how rates of activity change through time and space, link 3 Department of Earth Sciences, Uppsala Universitet, with tectonic, glacial/interglacial and climate cycles. Villavägen 16, Uppsala, Sweden (present address)

The huge potential for information to be gained by The Palaeogene Ben Hiant Member of Ardnamurchan, observing ocean drilling cores can be complicated by the NW Scotland, comprises a thick sequence of breccias and uncertainties associated with many physical processes. conglomerates interpreted as debris flow deposits (Brown & These uncertainties occur during eruption, through Bell 2007). These rocks are unconformably overlain by a transport, to deposition, burial, coring and the eventual recently identified sequence of pyroclastic rocks, which we identification and measurement of ash layers. If these interpret as ignimbrites. We propose the name the uncertainties can be quantified then it is possible to analyse ‘Stallachan Dubha Ignimbrite Member’ for these rocks. the record by stochastic ensemble models. Silicic explosive eruptions generated pyroclastic density currents that deposited a range of ignimbrite lithofacies. The cores we have focused on are those from the Lateral thickness variations in the ignimbrites record the Integrated Ocean Drilling Program (IODP), Ocean Drilling localised filling of the palaeotopography. Periodically, the Program (ODP) and the Deep Dea Drilling Program pyroclastic density currents entered small lakes and the ash (DSDP). Data are initially being gathered from literature was subject to aqueous reworking. generated by IODP, with a series of ground truthing Three phases of eruption have been recognised in the campaigns to rigourously test the quality of this data. sequence. Phase 1 was marked by the emplacement of Alternative approaches to data collection are being rheomorphic tuffs and breccias. The rheomorphic tuffs attempted to use the physical properties data to identify ash display a strong flow-fabric/parataxitic texture and folds are layers. This indends to make ash layer identification and locally present. The tuffs coarsen up in to a massive lithic measurement more consistent, and create a more complete breccia which contains boulders of the rheomorphic tuff and ash layer record. local country rock, before fining to rheomorphic tuff. The massive lithic breccia records a significant increase in mass flux, perhaps related to a high-energy vent clearing event, and/or vent collapse, and/or erosion of the substrate. Phase 2 is marked by the emplacement of a sequence of stratified tuffs, lapilli-tuffs and breccias. The tuffs and lapilli-tuffs are planar- to cross-stratified and alternate with massive lapilli-tuffs and breccias. In the finer units, convolute laminae and ripples are present. These rocks record the entry of a dilute pyroclastic density current into a small lake and the aqueous reworking of finer pyroclasts. Phase 3 is marked by the emplacement of a valley- filling crystal-rich massive lapilli-tuff. This unit unconformably overlies both Phase 1 and 2 rocks, including siltstones interpreted as lacustrine deposits associated with Phase 2. The lapilli-tuff comprises up to 50% crystals of plagioclase feldspar in an ashy matrix. Locally, breccia lenses, dominated by clasts of Phase 1 rheomorphic ignimbrite are present.

Brown, D., Bell, B., (2007) Bulletin of Volcanology 69, 847-868.

98 VMSG 2013 – Poster Presentation Abstracts

The respiratory health hazard of Exploring the mechanisms of volcanic ash: Factors affecting the basaltic fragmentation: Insights formation and toxicity of from textural analysis

cristobalite E.J. NICHOLSON*1, K.V. CASHMAN1, A. RUST1 C. NATTRASS*1, C. HORWELL1 1 Department of Earth Sciences, University of Bristol, Wills Memorial Building, Bristol (*[email protected]) 1 Institute of Hazard, Risk & Resilience, Department of

Earth Sciences, Durham University, Science Labs., Explosive volcanism can generate large volumes of South Road, Durham, DH1 3LE, UK volcanic ash, with potentially significant economic and (*[email protected]) environmental implications. Recent eruptions, such as that

of Eyjafjallajokull in 2010, have highlighted the need for Concern of the potential respiratory health hazard posed improved understanding of both the mechanisms involved by exposure to volcanic ash was raised after the 1980 in ash generation and the controls on the size distribution eruption of Mount St Helens, due to high concentrations of and morphology of erupted pyroclasts. Mafic eruptions, in crystalline silica in the ash. The toxic potential of crystalline particular, exhibit a wide range of eruption styles that silica is well-known and the silica polymorphs quartz and generate pyroclasts with variable sizes, shapes, cristobalite are known carcinogens. Volcanic ash can vesicularities and crystallinities. We are investigating links contain up to 23 wt.% crystalline silica (Horwell et al., between eruption style and pyroclast characteristics, with 2010), however toxicological studies have shown that the the goal of using these data both to gain insight into the ash produces a much lower toxic response than would be processes governing fragmentation and to develop expected for a dust containing this proportion of crystalline characteristic source parameters for different eruption silica. conditions Volcanic cristobalite is formed metastably in volcanic We are examining tephra samples from basaltic domes by vapour-phase deposition and the devitrification of eruptions ranging from magmatic to phreatomagmatic and glass. Temperatures in the volcanic dome setting are with crystallinities from negligible to >50%. Preliminary typically <850 °C, much lower than the 1470 °C needed to analyses show that fragmentation in these samples cannot form stable cristobalite. Collapse of these unstable domes be simply explained by expansion and interaction of generates highly respirable, cristobalite-rich volcanic ash. exsolving bubbles (that is, the fragmentation mechanism Substitutions of up to 3 wt. % Al O into the cristobalite 2 3 commonly attributed to silicic magmas). For example, ash structure have been observed (Horwell et al., in review) and from the 2011 subglacial eruption of Grimsvötn, Iceland, we hypothesise that these impurities allow the formation of consists largely of broken, dense glass, with less abundant cristobalite within the dome environment and affect the irregularly shaped glass shards formed from the interstices toxic potential of the cristobalite within the ash. of a population of large bubbles exhibiting a relatively Laboratory studies synthesising crystalline silica from narrow size distribution (bubble diameters of 10-50 um). an amorphous colloidal silica sol have shown that with the These data contrast with the moderately to highly vesicular addition of Al and Na impurities a pure cristobalite phase clasts produced by Hawaiian-style fire fountains. They also can be formed at temperatures lower than the 1470 °C contrast with pyroclasts from magmatic eruptions of mafic threshold. Under the same conditions pure silica, with no arc volcanoes, such as Fuego, Guatemala, which are highly added impurities, formed tridymite, demonstrating the crystalline and poorly to moderately vesicular. Together this addition of impurities alone can alter the silica polymorph small survey raises interesting questions about both where, produced. However, further work is needed to constrain how, and when gas loss occurs in mafic eruptions and the conditions needed for cristobalite formation at temperatures role of crystals in the fragmentation process. found within volcanic dome systems. Future toxicological tests on these synthetic samples will help gain an insight as to whether impurities can affect the toxicity of crystalline silica and the implications this has for the volcanic ash respiratory hazard.

Horwell et al. (2010) Bulletin of Volcanology 72:249–253 Horwell et al. (In review) Particle and Fibre Toxicology

99 VMSG 2013 – Poster Presentation Abstracts

Deforming a volcano by surface Pele’s tears and spheres – insights deposit loading: How loading may into the fragmentation of low mislead classic deformation viscosity magmas

analyses L.A. PORRITT*1, 2, J.K. RUSSELL2, S.L. QUANE3 H. ODBERT*1, B. TAISNE2 , S. TAIT3 1 University of Bristol, Bristol, UK. (*[email protected]) 2 University of British Columbia, Vancouver, Canada. 1 School of Earth Sciences, University of Bristol, UK. 3 Quest University Canada, Squamish, Canada. (*[email protected])

2 Earth Observatory of Singapore, Singapore. Pele’s tears are a well known curiosity commonly 3 Institut de Physique du Globe de Paris, France. associated with low viscosity basaltic explosive eruptions. However, these pyroclasts are rarely studied in detail and The deformation of a volcanic edifice before, during there is no full explanation for their formation. These and after an eruption is often interpreted as a response to intriguing pyroclasts have smooth glassy surfaces, pressurisation or depressurisation of parts of the magmatic vesiculated interiors, and fluidal morphologies tending system below ground (e.g. magma reservoirs). Typically, towards droplets and then spheres as they decrease in size to surface displacements are compared to numerical models to <2 mm. We present a detailed characterisation of Pele’s estimate the elastic response of the crust to such tears from the 1959 fire-fountaining eruption of Kilauea Iki pressurisation. Model inversion techniques are routinely involving size and density measurements. Using thin section used to infer the size, shape and volume or pressure change and SEM analysis we also consider their internal and of pressure sources using these kinds of models. A ‘best fit’ external morphologies, porosity and bubble size solution is obtained by minimising the misfit between the distributions, and surface textures. Finally we consider the modelled and observed ground displacements. This allows mechanisms of magma fragmentation, timescales of the system parameters of interest to be constrained. Such relaxation, and cooling rates that are responsible for their approaches require a number of simplifying assumptions formation. and typically neglect the influence of complicating factors, such as compressibility of magma in the system and the Porritt, L.A., Russell, J.K., Quane, S.L. (2012) Earth and crustal response to surface loading of erupted material (i.e. Planetary Science Letters 333-334, 171-180. lava domes, pyroclastic density current deposits, etc.). Here, we explore the effects a deposit load on ground displacement, and how they compare to deformation from classic burried pressure point source models. Over 1 km3 of lava has been erupted since 1995 by the Soufrière Hills Volcano, Montserrat. Much of this material has moved offshore but there remains a substantial subaerial and submarine deposit around the volcano’s flank. We measure the distribution of deposits, and hence the load, around the flanks of the volcano using recent topographic survey data. We then model the elastic crustal response of the deposit load across Montserrat, in terms of expected associated ground deformation. We discuss our results in the context of deformation source model inversions and show how such inversions may be mislead when loading is neglected.

100 VMSG 2013 – Poster Presentation Abstracts

The atmospheric habit of fine The sky’s the limit: Mapping volcanic ash volcanic deposits using kites

G.S. PRATA*1, B.E. REED2, T.A. MATHER1, D.M. J. STONE*1,3, J. BARCLAY1, P. COLE2, S. LOUGHLIN3, P. PYLE1, D.M. PETERS2 SIMMONS1 1 Dept. of Earth Sciences, University of Oxford 1 University of East Anglia. (* [email protected]) (*[email protected]) 2 Montserrat Volcano Observatory. 2 Department of Atmospheric, Oceanic and Planetary 3 Britisth Geological Survey. Physics (AOPP), Clarendon Laboratory, University of Oxford Aerial photographs are very useful for mapping the extent and variability of volcanic products. However the Lack of information on the physical, compositional and acquisition of these images is often expensive and optical characteristics of volcanic ash and properties that infrequent, requiring the use of a helicopter or light aircraft. affect its residence time, aggregation and interaction with Kite Aerial Photography (KAP) can be a cheaper other atmospheric species (e.g. ash-nucleated ice) represents alternative, allowing for low altitude, high-resolution a major gap in basic knowledge and understanding. images to be rapidly and frequently taken. A camera can be Measurements of the physical, compositional and optical attached to a kite and flown over a deposit, with vertical properties of fine ash are needed as input for radiative images stitched together to form a mosaic. Using KAP in transfer models and dispersion models (e.g. Stohl et al., Montserrat, a group of volunteer scientists from the local 1998; Costa et al., 2006). A comprehensive database of Community College took a series of aerial photographs of a information for dispersion models will provide useful data river valley at various times before and after lahars to for environmental impact assessments (e.g. human, animal document geomorphic change. The method produced some and plant health impacts) and at a fundamental level provide very promising results and has acted as a conduit for public new information for studying volcano-climate interactions involvement in monitoring. This project has demonstrated (e.g. Watson, 1997; Robock, 2000; Durant et al., 2010). the low cost and relative ease of this method in a volcanic These new measurements will also be very valuable for setting. Depending on the type of camera used, future satellite retrievals of volcanic ash that rely on assumptions applications could vary from photographs to of the optical properties, size distribution and morphology photogrammetry and the generation of DEM’s. of ash particles (e.g. Prata, 1989; Wen & Rose, 1994; Prata & Grant, 2001). The overall aim of this research is to fill an important gap in our understanding of the atmospheric habit of fine volcanic ash and processes governing its sedimentation.

Costa A., Macedonio G. & Folch A. (2006) Earth and Planetary Science Letters 241, 634-647. Durant A., Bonadonna C. & Horwell C. (2010) Elements 6, 235-240. Prata A. J. (1989) Geophysical Research Letters 16, 1293- 1296. Prata A. J. & Grant I. F. (2001) Quarterly Journal of the Royal Meteorological Society 127, 2153-2179. Robock, A. (2000) Reviews of Geophysics, 38, 191-219. Stohl A., Hittenberger M. & Wotawa G. (1998) Atmospheric Environment 32, 4245-4264. Watson A. J. (1997) Nature 385, 587-588. Wen S. & Rose W. (1994) J. Geophys. Res 99, 5421-5431.

101 VMSG 2013 – Poster Presentation Abstracts

Strombolian to phreatomagmatic Towards quantifying the arc-scale explosive eruption: The Cova de and global magmatic response to Paúl Crater eruption on Santo deglaciation

Antão, Cape Verde Islands S. WATT*1, D. PYLE2, T. MATHER2 R.W. TARFF *1, S.J. DAY2 1 Ocean and Earth Science, National Oceanography Centre Southampton, University of Southampton Waterfront 1 Department of Earth and Planetary Sciences, Birkbeck Campus, European Way, Southampton SO14 3ZH, UK University of London. (*[email protected]) 2 (*[email protected]) Aon Benfield UCL Hazard Research Center, Department 2 Department of Earth Sciences, University of Oxford of Earth Sciences, University College, London.

There is a growing body of evidence that the retreat of Episodes of hazardous phreatomagmatic explosive ice sheets after the last glacial maximum (LGM) resulted in activity, often prolonged and complex, occur within temporarily enhanced levels of volcanism. This has been eruptions at high-elevation vents on many oceanic island postulated on the scale of individual edifices, and on volcanoes. The water driving these explosions is sourced regional scales in intraplate and rift settings. It has been from freshwater aquifers within the volcanic edifices. An proposed that this pattern was of global significance in understanding of how groundwater enters the eruption contributing to rising atmospheric CO concentrations, and conduits is key to effective warning and mitigation of the 2 thereby formed a feedback process for global warming. resulting hazards, including an understanding of how long However, the impact of deglaciation on volcanic arcs has such eruptions may last. Here we describe near-vent been incompletely explored. Volcanic arcs account for 90% deposits from a single prehistoric eruption at the large Cova of present-day subaerial volcanic eruptions, and for de Paúl crater on the island of Santo Antão, Cape Verde volcanically-sourced volatiles they are of first-order Islands that included both mild Strombolian magmatic and significance. Without understanding fluctuations in arc violently explosive phreatomagmatic activity. The volcanic output, an assessment of global changes in phreatomagmatic sequence includes extensive low- volcanic activity cannot be made. temperature, lithic-rich phreatomagmatic pyroclastic flow Here, we present the first systematic assessment of the and surge deposits, indicating a prolonged series of more response of glaciated volcanic arcs to deglaciation. By using and less violent explosive episodes whose characteristics comprehensive compilations of eruption records from are indicated by variations in clast size distributions and southern Chile, augmented by records from the Cascade and clast assemblages. The underlying Strombolian deposits, Kamchatka arcs, we show that the post-glacial increase in which grade up from welded spatter to unwelded, often volcanism was relatively small in comparison to non-arc blocky scoria, contain distinctive strongly flow-banded volcano-tectonic settings. Where ice unloading was at its angular sub-glassy clasts. These also form a distinct bed of greatest, eruption frequency approximately doubled for ~5 large clasts at just below the phreatomagmatic deposits. kyr, but this pattern is at the limit of statistical significance. Comparison of these clasts with the Strombolian scoria The same period coincides with a few notably large indicates that they are fragments of chilled margins from the explosive eruptions. In less heavily glaciated regions, no walls of the eruptive conduit. Disintegration of the chilled pattern can be deduced at the resolution of available data. margin allowed a sudden increase in groundwater flow into While eruption patterns are commonly episodic, the timing the conduit causing the onset of the phreatomagmatic of increases in activity does not always show a clear link to explosive phase of the eruption. Subsequent variations in deglaciation. groundwater influx rates as different parts of the In light of the above, we critically examine available groundwater aquifer drained into the conduit may explain eruption records in an effort to constrain global-scale the many explosions recorded by the complex changes in volcanic output. Great caution must be exercised phreatomagmatic sequence. when attempting to quantify variation in volcanism from such data. Due to extremely sparse sampling (i.e. highly incomplete data), temporal and spatial biases must be corrected. Spatial variation in sampling rates is particularly significant. In some highly active volcanic regions, such as Indonesia, as few as 1 in 20,000 VEI ≥2 eruptions have been identified during the 5–20 ka time period. Globally, >99% of all eruptions of VEI ≥2 have not been identified. Because of this, variations in eruption rate between glaciated and non-glaciated regions cannot be precisely quantified. We suggest that, at most, global eruption rates may have doubled after the last glaciation, from 13–7 ka. Although volcanism may have been an important source of

CO2 in the early Holocene, it cannot have been a dominant

control on changes in atmospheric CO2 after the LGM. To improve our ability to constrain global-scale patterns in magmatic processes, there is a need for improved records of past volcanic activity, particularly from several low-latitude regions, where data are extremely sparse.

102 VMSG 2013 – Poster Presentation Abstracts

Constraints on the physical Effusive activity at Somma- characteristics of volcanic activity Vesuvius: lava flow-field on Venus characteristics from 1631 to 1944

M.W. AIREY*1, T. A. MATHER1, D. M. PYLE1 S.K. BROWN*1,2, M.C. SOLANA1, C.R.J. KILBURN3 1 University of Oxford, UK. (*[email protected]) 1 School of Earth and Enivironmental Sciences, University of Portsmouth, Burnaby Building, Burnaby Road, Volcanoes and their deposits are ubiquitous on Venus, Portsmouth, PO1 3QL. (*[email protected]) being some of the most recognisable geological phenomena 2 School of Earth Sciences, University of Bristol, Wills in the surface record. Clues to their origin, mode of Memorial Building, Queen’s Road, Bristol BS8 1RJ. formation, composition, and style of eruption can be 3 Aeon-Benfield Hazard Research Centre, UCL, Gower St., gathered on inspection of the wealth of data acquired over London WC1E 6TP. more than 50 years of modern Venus observation, from the Russian probes and landers of the 60s, 70s, and 80s, through Vesuvius in southern Italy is among the most densely Magellan’s mapping cycles in the 90s to the highly populated active volcanoes. Although famous for its successful Venus Express spacecraft operational today. destructive Plinian eruptions, its recent activity, between The style of volcanic activity on Venus differs from that 1631 and 1944, was primarily effusive and Strombolian, on Earth due to the very different prevailing conditions into producing numerous lava flows that inundated the which they erupt; Venus has a surface temperature of ~730 populated lower slopes. K and a surface pressure of ~92 Earth atmospheres (Kliore, Here we present data compiled for 183 eruptions during et al., 1986). When conducting an investigation into what the last eruptive period, with additional data regarding all may characterise the eruptive style of volcanoes under these major flank events. These eruptions fed the emplacement of conditions, a broad array of environmental, chemical, and lava flow-fields which on average reached 4km in length, physical factors must be considered. with a maximum length identified of <8km. Both simple The core of this investigation was based on the linking and compound flow-fields are recognised, with typical of two previously developed models of volcanic processes surface areas of less than 5km2, and approximately two- that can be parameterised for Venusian conditions. The thirds achieved their maximum lengths after more than one conduit flow model ‘Conflow’ (Mastin, 2011) in order to week. simulate processes below the surface and the volcanic Although most activity was focussed at the summit, plume model described in Glaze & Baloga (1996) in order flank vents also developed with lava flow-fields affecting to simulate processes above the surface. The approach taken correspondingly distal areas. Eccentric vents formed in the here is to conduct a comprehensive study of the mass flux southern edifice at approximately 300m above sea level at a threshold (by way of vent diameter as a proxy) between mean distance of 4.2km from the summit. A submarine pit buoyancy and collapse using realistic assumptions of initial crater, newly correlated with the 1861 eruption, highlights physical and geological conditions to obtain a best estimate the potential for vent development at low altitudes. of the initial vent parameters with which to calculate the Flank vents normally developed when the summit crater threshold boundaries at various temperatures, volatile had filled with lavas, and eccentric vents were preceded by contents, and elevations. These findings were then three days of increased felt seismicity. Such events can thus compared with case studies derived from the Magellan radar potentially be forecast with at least a 24-hour warning, and data set. even after the onset of eruption, several days may be When selecting case studies, localities were sought that available before a settlement is threatened. The design of provide examples of deposits that suggest a range of styles an effective emergency response to future effusions is thus a of volcanic activity upon which to test the models and feasible objective. impose constraints upon volcanic processes. Once selected, the available satellite data (primarily from the Magellan data repository) from the subject region was acquired and, from those, the values of various measured/derived surface properties could be extracted upon which to base the interpretation of the corresponding volcanic terrains in question. Results from the explosivity/buoyancy modelling study were then used in conjunction with the interpretation of the terrains to provide constraints on the eruption parameters suggested by the various observed deposits.

Glaze, L. S., and Baloga, S. M. (1996) Sensitivity of buoyant plume heights to ambient atmospheric conditions: Implications for volcanic eruption columns, J. Geophys. Res.-Atmos., 101, 1529-1540. Kliore, A. J., Moroz, V. I., and Keating, G. M. (1986) The Venus International Reference Atmosphere, Pergamon Press, Oxford.; Mastin, L. G. (2011) Conflow v1.0.5, http://vhub.org/resources/453.

103 VMSG 2013 – Poster Presentation Abstracts

Lava channel networks Kalkarindji - the forgotten volcanic H.R. DIETTERICH*1, K.V. CASHMAN 1,2 province 1 Department of Geological Sciences, University of Oregon, P.E. MARSHALL*1, M. WIDDOWSON1 Eugene, Oregon, USA. (*[email protected]) 1 Volcano Dynamics Group, Envinronment, Earth & 2 School of Earth Sciences, University of Bristol, Bristol, Ecosystems, The Open University, Walton Hall, Milton UK. Keynes, UK. MK7 6AA. (*[email protected])

A crucial question for assessing lava flow hazard, as Kalkarindji, the oldest Phanerozoic continental flood well as understanding flow emplacement at volcanoes basalt province (CFBP), covers a large part of the northern around the world and on other terrestrial planets, is what Australian desert, being well preserved due to its location controls the lengths of lava flows. John Guest sought to on the stable Australian craton. The province enjoys an answer this question by investigating the emplacement of anonymity not usually afforded to structures of this size, lava flows at Mt Etna that, despite very different eruptive due mainly to this remote location. Dated at 505-510 Ma, rates and durations, yielded flows of the same final length the province now consists of scattered basaltic suites across (Guest et al., 1987). This observation can also be made of northern and central Australia, which if connected indicate a Hawaiian lava flows, many of which have a length of ~ 25 minimum eruptive volume of 1.5 ϰ 105 km3. km regardless of effusion rate, except where the longer The most extensive of these suites, the Antrim Plateau flows have been topographically confined into single Volcanics (APV), lies SE of Lake Argyle, stretching for channels. We hypothesize that both flow length and 400,000 km2 with thicknesses of 0.7 - 1.1 km. They are advance rate of Hawaiian lava is modulated by the predominantly evolved, low-Ti tholeiitic basaltic andesites development of complex channel networks. exhibiting extreme crustal contamination signatures. To analyze the creation of lava channel networks, we Therefore, the composition of the Kalkarindji lavas are focus on the bifurcations and confluences that create them. quite distinct from other tholeiitic CFBP successions. We hypothesize that flow interaction with topographic Field reconnaissance reveals flow units to be thick (40 - obstacles will result in flow splitting, while flow 60 m) sheet-like aphanitic basalt with vesiculated or rubbly confluences will be driven by topographic confinement or flow-tops. Four different flow types, seen throughout the the merging of parallel lobes due to lateral spreading. Our province, are identified, based on geochemistry, analysis of the Hawaiian channel networks reveals that morphology and volcanolgy. We present new data from greater pre-eruptive slopes correlate with more parallel boreholes and field samples, building up a channels, supporting that flow height, which is reduced on volcanostratigraphy across the APV. steeper slopes, could control bifurcation formation.

However, in analogue experiments, flows are able to overtop obstacles at high velocity when a bow wave thickens the flow upslope of the obstacle. We also document how cooling influences confluence formation after a bifurcation with molten basalt experiments that show that levee formation inhibits the formation of confluences between parallel flow lobes. Further analysis of lava channels as interconnected networks, combined with an investigation of flow thickness, yields insight into the evolution of channel networks during emplacement. This work has implications for flow prediction, diversion barriers, and the interpretation of terrestrial and planetary lava channel networks and flow morphology.

Guest, J.E., Kilburn, C.R.J., Pinkerton, H., and Duncan, A.M., (1987) Bulletin of Volcanology 49, 527-540.

104 VMSG 2013 – Poster Presentation Abstracts

Levee control on the evolution of Inflation, drainage and lava-water lava flow fields interaction during the emplacement

M. NOLAN*1, M.C. SOLANA2, C.R.J. KILBURN3 of the Nesjahraun, Iceland 1 SEES, Burnaby Building, Burnaby Road, Portsmouth, PO1 J.A STEVENSON*1, N.C. MITCHELL2, M. CASSIDY3, H. 3QL PINKERTON4 2 Aeon-Benfield Hazard research Centre, UCL, Gower St., 1 School of Geosciences, University of Edinburgh. London WC1E 6TP (*[email protected])

2 S.E.A.E.S. University of Manchester Traditional lava flows studies (e.g. Guest et al 1987, 3 National Oceanography Centre, University of Kilburn and Lopes 1988, Kilburn and Lopes 1991) Southampton established five mechanisms controlling the growth of flow- 4 Lancaster Environment Centre, University of Lancaster fields: New flows originating from the vent, Breaching of levees, Breaching/ reactivation of fronts, Bifurcation of This study describes the emplacement of the channels and Nesjahraun, a basaltic lava flow that entered the lake Overtopping. An analysis of the frequency of these Þingvallavatn, SW Iceland. It combines LiDAR, sidescan mechanisms showed that breaching is one of the most sonar and Chirp seismic data with field observations to map important process for the growth of flow fields. Breaches the flow field and investigate the varied behaviour of the from the medial sides of lava channels on Etna frequently lava. occur where a pulse of lava stops and inflates and is clearly The lava in the central part of the flow field has a platy- favoured by topography. Even slight topographical ridged surface, similar to other lava flows in Iceland and on irregularities favour the deformation and breaching of Mars. This is interpreted to have formed by unsteady channels. On slopes with a lower gradient the sinuosity in inflation of the brittle crust of stationary sheet pāhoehoe, lava channels increases and in 57% of the cases examined, causing it to break into plates. The ridges of broken curvature of the channel led to breakouts or over-topping. In pāhoehoe slabs formed as the plates of crust moved the majority of these instances, the breakout occurred on the vertically past each other in a process similar to the outside bend of the flow. formation of shatter rings. Along the shoreline, stacks of Rock mechanic tests on levee samples confirmed that thin (5–20 cm thick), vesicular, flows rest upon and the strength and mode of failure varied substantially surround low (<5 m) piles of coarse, unconsolidated, between levee types and even between different orientations variably oxidised spatter. Offshore from the pāhoehoe lavas, within the same levee. The alignment of crystals and the gradient of the flow surface steepens, suggesting a vesicles also had a significant impact in reducing the change in flow regime and the development of a talus ramp. strength of the rock. As expected, “massive” levee types Formation of a 250-m-wide open channel through the with low vesicularity were found to be the most resistant flow field allowed the inflated central part of the flow to and “rubbly” the weakest. drain rapidly, flowing as ‘a‘ā lava that eroded the channel

walls, carrying broken pāhoehoe slabs, lava balls and rafts

of compound shelly pāhoehoe lava and leaving a network of drained channels and tubes in the upstream part of the flow.

The ‘a‘ā channel split into individual flow lobes 20–50 m wide along the shore. ‘A‘ā clinker is exposed on the water’s

edge, as well as glassy sand and gravel, which has been locally intruded by small (<1 m), irregularly shaped, lava bodies. Mounds consisting predominantly of scoria lapilli and the large paired half-cone of Grámelur were formed in phreatomagmatic explosions. The ‘a‘ā flow can be identified underwater over 1 km offshore, and the sidescan data show that the flow lobes remained coherent flowing down a gradient of <10°. We suggest that formation of this type of platy-ridged lava, where the plates are smooth and the ridges are slabs of broken pāhoehoe, can occur without significant horizontal transport, as the surface crust is broken into plates in situ. The Nesjahraun demonstrates that, even in the absence of ocean waves, phreatomagmatic explosions are ubiquitous and that pāhoehoe flows are much more likely to break up on entering water than ‘a‘ā flows, which, with a higher flux and shallow underlying surface gradient, can penetrate water and remain coherent over distances of at least 1 km.

105 VMSG 2013 – List of Delegates

Delegate List Name E-mail Institution Martin Airey [email protected] University of Oxford Paul Albert [email protected] Royal Holloway Jens Andersen [email protected] University of Exeter

Paul Anderson [email protected] University of Birmingham

Catherine Annen [email protected] University of Bristol

Chris Arkwright [email protected] The Open University

Willy Aspinall [email protected] University of Bristol

Melanie Auker [email protected] University of Bristol

Jenni Barclay [email protected] University of East Anglia

Dan Barfod [email protected] SUERC

Heidi Barnes [email protected]

Andrew Beard [email protected] Birkbeck

Samuel Bewick [email protected] Open University

Juliet Biggs [email protected] University of Bristol

Stephen Blake [email protected] The Open University

Jon Blundy [email protected] University of Bristol

John Bowles [email protected] University of Manchester

Julie Boyce [email protected] Monash University

Mike Branney [email protected] University of Leicester

Richard Bretton [email protected] University of Bristol

Michael Broadley [email protected] University of Manchester

Richard Brooker [email protected] University of Bristol

David Brown [email protected] University of Glasgow

Sarah Brown [email protected] The University of Bristol

John Browning [email protected] Lancaster University

David Budd [email protected] Uppsala University

Liam Bullock [email protected] Keele University

Rose Burden [email protected] University of Bristol

Anthony Burnham [email protected] University of Bristol

Bethan Burson [email protected] Open University

Luca Caricchi [email protected] University of Geneva

Kathy Cashman [email protected] University of Bristol

Michael Cassidy [email protected] University of Southampton

Janet Catchpole [email protected]

Ana Carracedo [email protected] SUERC

David Chester [email protected] University of Liverpool

Paul Cole [email protected] Plymouth University

Frances Cooper [email protected] University of Bristol

Maya Coussens [email protected] Southampton University

Paul Cragg [email protected]

Elizabeth Cramer [email protected] The Open University

Annabel Crowther [email protected] Cambridge University

Julia Crummy [email protected] University of Leeds

Börje Dahren [email protected] Uppsala University

Jon Davidson [email protected] University of Durham

Alistair Davies [email protected] University of Cambridge

Simon Day [email protected] University College London

Sarah Henton De Angelis [email protected] University of Alaska Fairbanks

Alexandra De Joux [email protected] University of Edinburgh

Rodrigo Del Potro [email protected] University of Bristol

Philippa Demonte [email protected] Boise State University

Hannah Dietterich [email protected] University of Oregon

Jonathan Dietz [email protected] University of Glasgow

Mikel Diez [email protected] University of Bristol

Kate Dobson [email protected] University of Manchester

Amy Donovan [email protected] University of Cambridge

Simon Drake [email protected] Birkbeck

Angus Duncan [email protected] University of Bedfordshire

Susanna Ebmeier [email protected] University of Bristol

Marie Edmonds [email protected] University of Cambridge

Holly Elliott [email protected] University of Southampton

Ben Ellis [email protected] ETH Zurich

Fran Entwistle [email protected] University of Leeds

Laura Evenstar [email protected] University of Bristol

Peter Fawdon [email protected] The Open University

Carina Fearnley [email protected] Aberystwyth University

April Fitzgerald-Hudson [email protected] Keele University

Anne Forbes [email protected] The Open University

Heye Freymuth [email protected] University of Bristol

Raffaella Fusillo [email protected] University of Bristol

Thomas Gernon [email protected] University of Southampton

Ralf Gertisser [email protected] Keele University

Robin Gill [email protected] Royal Holloway

Amy Gilmer [email protected] University of Bristol

Joachim Gottsmann [email protected] University of Bristol

Tanya Gray [email protected] University of Bristol

Robert Green [email protected] University of Cambridge

David Green [email protected] AWE Blacknest

Tim Greenfield [email protected] University of Cambridge

106 VMSG 2013 – List of Delegates

Clayton Grove [email protected] University of Durham

Leanne Gunn [email protected] The Open University

Derya Gurer [email protected] University of Oslo

Jonathan Hanson [email protected] University of Bristol

Margaret Hartley [email protected] University of Cambridge

Ben Hayes [email protected] Cardiff University

Brioch Hemmings [email protected] University of Bristol

James Hickey [email protected] University of Bristol

Kelby Hicks [email protected] University of Cambridge

Anna Hicks [email protected] University of East Anglia

Melanie Hinrichs [email protected] The Open University

Murray Hoggett [email protected] University of Birmingham

Marian Holness [email protected] University of Cambridge

Eoghan Holohan [email protected] University College Dublin Adrian Hornby University of Liverpool

Martin Hughes [email protected] Mineralogical Society

Sion Hughes [email protected] The Open University

Hannah Hughes [email protected] Cardiff University

Madeleine Humphreys [email protected] University of Oxford

Will Hutchinson [email protected] University of Oxford

Evgenia Ilyinskaya [email protected] Bristish Geological Survey

Paul Jarvis [email protected] University of Bristol

Alia Jasim [email protected] University of Bristol

Adam Jeffrey [email protected] Keele University

Susanna Jenkins [email protected] University of Bristol

Eleanor Jennings [email protected] University of Cambridge

Lisa Jepson [email protected] University of Manchester

Dougal Jerram [email protected] Dougal Earth Limited

Emma Johnston [email protected] University of Bristol

Adrian Jones [email protected] University College London

Rosie Jones [email protected] The University of Edinburgh

Nina Jordan [email protected] University of Leicester

Maren Kahl [email protected] University of Leeds

Jessica Kandlbauer [email protected] University of Bristol

Michael Kendall [email protected] University of Bristol

Jackie Kendrick [email protected] Ludwig-Maximilan University

Christopher Kilburn [email protected] University College London

Geoff Kilgour [email protected] University of Bristol

Marthe Klocking [email protected] University of Cambridge

Tom Knott [email protected] University of Leicester

Stefan Lachowycz [email protected] University of Oxford

Oliver Lamb [email protected] University of Oxford Yan Lavallee University of Liverpool

Phillip Leat [email protected] British Antarctic Survey

Julien Leuthold [email protected] University of Bristol

David Litchfield [email protected] University College London

Marion Louvel [email protected] Institut Neel

John Maclennan [email protected] University of Cambridge

Heidy Mader [email protected] University of Bristol

Craig Magee [email protected] Imperial College

Sue Mahony [email protected] University of Bristol

Ben Manton [email protected] Cardiff University

Freya Marks [email protected]

Peter Marshall [email protected] The Open University

Tamsin Mather [email protected] University of Oxford

Hannes Mattsson [email protected] ETH Zurich

Brendan McCormick [email protected] Queens College

Dave McGarvie [email protected] The Open University

Iona McIntosh [email protected] Durham University

Charlotte McLean [email protected] University of Glasgow

Claire McLeod [email protected] University of Houston

Sorcha McMahon [email protected] University of Bristol

Fiona Meade [email protected] Uppsala University

Ian Meighan [email protected] SUERC

Vali Memeti [email protected] University of Durham

Hilary Milroy [email protected] University of Bristol

Helena Moretti [email protected] University of Bristol

Dan Morgan [email protected] University of Leeds

Duncan Muir [email protected] University of Bristol

Cyril Muller [email protected] University of Bristol

Irving Munguia [email protected] University of Bristol

Laura Murdoch [email protected] University of Strathclyde

Joanne Murray [email protected] University of Birmingham

John Murray [email protected] The Open University

Claire Nattrass [email protected] University of Durham

David Neave [email protected] University of Cambridge

Peter Nicholls [email protected] Uppsala University

Emma Nicholson [email protected] University of Bristol

Graeme Nicoll [email protected] Neftex

Svetlana Novikova [email protected] University of Cambridge

Andy Nowacki [email protected] University of Bristol

Henry Odbert [email protected] University of Bristol

107 VMSG 2013 – List of Delegates

Julie Oppenheimer [email protected] University of Bristol

Pablo Palacios [email protected] University of Bristol

Kris Palubicki [email protected] The Open University

Matthew Pankhurst [email protected] University of Leeds

Amy Parker [email protected] University of Bristol

Chiara Maria Petrone [email protected] The Natural History Museum

Stacy Phillips [email protected] Memorial University of Newfoundland

Jeremy Phillips [email protected] University of Bristol

Joe Pickles [email protected] University of Bristol

Mattia Pistone [email protected] ETH Zurich

Melissa Plail [email protected] University of East Anglia

Lucy Porritt [email protected] University of Bristol

Gemma Prata [email protected] University of Oxford

Katie Preece [email protected] University of East Anglia

Jacqueline Ratner [email protected] University of Oxford

Heather Rawcliffe [email protected] University of Glasgow

Marco Reichow [email protected] University of Leicester

Peter Reynolds [email protected] University of Durham

Hannah Reynolds [email protected] Lancaster University

Jenny Riker [email protected] University of Bristol

Teal Riley [email protected] British Antarctic Survey

Elspeth Robertson [email protected] University of Bristol

Mel Rodgers [email protected] University of South Florida

Alison Rust [email protected] Bristol University

Hazel Rymer [email protected] The Open University

Lois Salem [email protected] University of Cambridge

Christopher Satow [email protected] Royal Holloway

Kate Saunders [email protected] University of Bristol

Andy Saunders [email protected] University of Leicester

Nick Schofield [email protected] University of Birmingham

Anne Schopa [email protected] University of Bristol

Thomas Sheldrake [email protected] University of Bristol

Jessica Shields [email protected] University of Bristol

Isobel Sides [email protected] University of Cambridge

Bethany Simons [email protected] Cambourne School of Mines

Susanne Skora [email protected] University of Bristol

Jean-Francois Smekens [email protected] Arizona State University

Vicki Smith [email protected] University of Oxford

Kate Smith [email protected] University of Exeter

Carmen Solana [email protected] University of Portsmouth

Stephen Sparks [email protected] Bristol University

Charlotte Stamper [email protected] University of Bristol

John Stevenson [email protected] University of Edinburgh

Michael Stock [email protected] University of Oxford

Ellen Stofan [email protected]

Jonathan Stone [email protected] University of East Anglia

Karen Strehlow [email protected] University of Bristol

Finlay Stuart [email protected] SUERC

Elizabeth Swanson [email protected] University of Bristol

Yoshihiko Tamura [email protected] JAMSTEC

Bob Tarff [email protected] Birbeck College

Andrew Thomson [email protected] University of Bristol

Emma Tomlinson [email protected] Trinity College Dublin

Valentin Troll [email protected] Uppsala University

Marie Turnbull [email protected]

Marit Van Zalinge [email protected] University of Bristol

Geoff Wadge [email protected] University of Reading

Richard Wall [email protected] University College London

Matt Watson [email protected] University of Bristol

Sebastian Watt [email protected] Southampton University

Daniel Weidendorfer [email protected] ETH Zurich

Bradley West [email protected] University of Bristol

Robert White [email protected] Cambridge University

Rebecca Williams [email protected] University of Leicester

Lionel Wilson [email protected] Lancaster University

Penelope Wilson [email protected] Kingston University

Mark Woodhouse [email protected] University of Bristol

Christine Yallup [email protected] University of Cambridge

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