ERUPTIVE DYNAMICS AND PETROLOGICAL EVOLUTION OF RECENT VOLCANISM ON THE EL HIERRO ISLAND. IMPLICATIONS FOR VOLCANIC HAZARD ASSESSMENT PhD Thesis Stavros Meletlidis Tsiogalos Barcelona 2017 Eruptive dynamics and petrological evolution of recent volcanism on the El Hierro Island. Implications for volcanic hazard assessment by Stavros Meletlidis Tsiogalos A thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy Programa de Doctorat de "Ciències de la Terra" Department of Geodynamic and Geophysics Faculty of Geology Universidad de Barcelona Thesis Supervisor: Prof. Joan Martí Molist Institute of Earth Sciences Jaume Almera - CSIC Thesis Tutor: Prof. Joan Manuel Vilaplana Fernández Faculty of Geology - UB June 2017 On the cover: Monogenetic volcano located in the west sector of El Hierro Island, by the lighthouse of Orchilla. Pahoehoe lava flows originating on the lower flank of the cone, fed by parasitic vents, can be distinguished. Photo: Stavros Meletlidis Eruptive dynamics and petrological evolution of recent volcanism on the El Hierro Island. Implications for volcanic hazard assessment Stavros Meletlidis Tsiogalos "ἓν οἶδα ὅτι οὐδὲν οἶδα" - Socrates (470 - 399 B.C.) - To Sonia, Paris & Hector, because they always understood ACKNOWLEDGEMENTS I would like to thank all the people who have contributed in some way to this thesis, without whose support and encouragement it would not have been possible. First and foremost, I thank my academic supervisor, Professor Joan Martí Molist, for supporting and guiding me through this journey. During this adventure he contributed to a rewarding PhD experience by giving me intellectual freedom in my work and engaging me in new ideas. Also a big thank you goes to my tutor Professor Joan Manuel Vilaplana Fernández, who had the patience to deal with me all this time and being a good listener and guide. This thesis would not have been possible without the generous support of the Instituto Geográfico Nacional (I.G.N.), where I work since 2007, which provided me with all the necessary infrastructure and logistical support. Every result achieved in this thesis was accomplished with the help and support of fellow workmates, not only from Tenerife office (Centro Geofísico de Canarias, del I.G.N.) but also from Observatorio Geofísico Central del I.G.N. (Madrid headquarters). Particularly thanks to Alicia Felpeto, Itahiza Dominguez, Pedro Torres, Laura Garcia, Sergio Sainz-Maza Aparicio and Carmen del Fresno Rodríguez-Portugal, for their friendship, support and help. You provided a friendly and cooperative atmosphere at work and also useful feedbacks and insightful comments on my work. I am still missing those endless days in the field or the nights in duty while the eruption. I was fortunate to have the chance to work under the direction of two exceptional women and scientists, María Jose Blanco (my boss in Tenerife) and Carmen Lopez (my big boss in Madrid). Their effort to understand my spanish-greek-english semi-constructed thoughts and their support to all my crazy ideas were gone beyond this world and to different extents. Particular thanks to the Italian team: Alessio, Massimo, Antonella and Paola. They have become my personal rescue team when times of storm and uncertainty drew near. I shared great moments with them, field work, lab work, and hours of discussion (thank you Skype!). Many times they were my source of scientific knowledge, and I am grateful for sharing and been taught, tirelessly and with much enthusiasm. I am also indebted to Professor Michael Fytikas, for introducing me in that "volcanic" world and giving me the possibility to work, learn and love volcanoes. I am very grateful to Dr. George Vougioukalakis who accepted and suffered, years ago, a graduate student as a teammate in his field work all over Greece, and passed me over his knowledge and his enthusiasm in studying the volcanoes. It's a pity that an ocean and a continent lay between us. I would like to acknowledge friends and family who have supported me during my time here. First and foremost I would like to thank my beloved spouse Sonia for her constant love and unyielding support. I am sure she will never forget these long periods of me away from home, monitoring El Hierro eruption, taking samples, working on monitor network deployment on other islands, congress trips or lab work abroad. Thank you for having faith in my work, standing behind me and sacrificing so many things. Also I would like to thank my two sons, Paris and Hector, they were always there to have my mind occupied (and my body) when too much work was accumulated. However, I have to apologize for the loss of so many moments due to my odd work and I hope that someday Hector could forgive me for abandoning him as a newborn (5 days of life) because of El Hierro eruption; Έκτωρα, το είδες; Τελικά τα καταφέραμε! To my Mom, Theodora, and my recently passed away Dad, Lazaros, all I have to say is thank you for the effort and support to make me study and also thanks for understanding and suffer these tons of rocks and laundry bags at home, whenever I returned from a field trip. To my parents-in-law, María and Belio, I want to thank you for being part of this, supporting and helping in every aspect of our family life. Without you, we would not have managed to survive. Finally, I would like to thank Chris Satow and Maite Martín González, for proof-reading the English manuscript and their constructive comments. Thanks, you all have my eternal gratitude and love Stavros June 2017 CONTENTS Abstract III 1. Introduction 1 1.1. Thesis overview - Canary Islands, magmas and eruptions 1 1.2. Products of a newborn volcano 6 1.3. An explosive felsic eruption on an oceanic island 11 1.4. Clarifying the dubious origin of the xenopumices 15 1.5. Modelling through instrumental data and erupted products 19 1.6. Not a calm basaltic eruption 27 2. Results 35 3. Discussion 51 4. Conclusions 63 5. References 67 6. Annexes 79 6.1. Meletlidis, S., A. Di Roberto, M. Pompilio, A. Bertagnini, I. Iribarren, A. Felpeto, P. A. Torres, and C. D'Oriano (2012). Xenopumices from the 2011-2012 submarine eruption of El Hierro (Canary Islands, Spain): Constraints on the plumbing system and magma ascent, Geophys. Res. Lett., doi:10.1029/2012GL052675 6.2. Pedrazzi, D., Becerril, L., Martí, J., Meletlidis, S., Galindo, I. (2014). Explosive felsic volcanism on El Hierro (Canary Islands). Bull of Volcanology, 76:863. doi: 10.1007/s00445-014-0863-1 6.3. S. Del Moro, A. Di Roberto, S. Meletlidis, M. Pompilio, A. Bertagnini, S. Agostini, F. Ridolfi, A. Renzulli (2015). Xenopumice erupted on 15 October 2011 offshore of El Hierro (Canary Islands): a subvolcanic snapshot of magmatic, hydrothermal and pyrometamorphic processes. Bull of Volcanology, Volume 77:53. doi: 10.1007/s00445-015-0940-0 6.4. S. Meletlidis, A. Di Roberto, I. Domínguez Cerdeña, M. Pompilio, L García-Cañada, A. Bertagnini, M. A. Benito-Saz, P. Del Carlo, S. Sainz-Maza Aparicio (2015). New insight into the 2011-2012 unrest and eruption of El Hierro Island (Canary Islands) based on integrated geophysical, geodetical and petrological data. Annals of Geophysics, [S.l.], v. 58, n. 5, p. S0546, doi: 10.4401/ag-6754 6.5. Di Roberto, A.; Bertagnini, A.; Del Carlo, P.; Meletlidis, S.; Pompilio, M. (2016). The 1909 Chinyero eruption on Tenerife (Canary Islands): insights from historical accounts, and tephrostratigraphic and geochemical data. Bull of Volcanology, 78:88. doi 10.1007/s00445-016-1083-7 I II ABSTRACT The Canarian archipelago, extends over approximately 500 km in total along the passive continental margin off NW Africa, comprises seven major and four minor islands, and it is part of the so called Macaronesia region, together with the archipelagos of Azores, Madeira, Salvajes and Cape Verde. Within the oceanic geodynamic context, the Canary archipelago is located on oceanic crust of the big African plate, specifically upon the passive continental margin, with thickness exceeding 20 km. It is a good example of oceanic intraplate alkaline volcanism. According the radioisotopic data available (Carracedo et al., 1998) the archipelago has been formed during the last 60 Ma and is still volcanically active. Multiple periods of volcanic activity accompanied with extreme range in magma compositions and eruptive styles have been exhibited during the evolution. A wide variety of models have been proposed for the origin of the Canary Islands, such as, hot spot, decompressing fusion, Atlas generated propagating fracture, or the "block" model based on regional fractures that helped elevate the islands. Holocene sub-aerial activity has occurred on all islands, except La Gomera, with 18 eruptions in the last 520 years (historic activity) on Tenerife, La Palma, Lanzarote and El Hierro. All these eruptive events consist of monogenetic basaltic eruptions along structures or zones identified as rifts (only the 1798 of Montaña Chahorra in Tenerife, expulsed intermediate composition magma and was located at the base of the Teide-Pico Viejo volcanic complex). Although monogenetic volcanism is the most extended type of volcanic activity on the planet (Walker 2000) and is characterized by a large diversity of eruptive styles and products, it is generally associated to low level volcanic hazard and many times it is underestimated in the hazard assessment. The main structures generated by these type of eruptions (concentrated as volcanic fields or long rift zones) are cinder cones, formed by the pyroclastic products and lava flows, that can reach several kilometres length. Eventually, can generate phreatomagmatic deposits, when an interaction between magma and water occurs (shallow submarine volcanism or littoral cones). These eruptions, traditionally, are associated with a single batch and pulse of magma and are greatly influenced by local and regional stress fields.