DOCSLIB.ORG

An Iceland Hotspot Saga

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
An Iceland Hotspot Saga Reviewed research article An Iceland hotspot saga Ingi Þorleifur Bjarnason Institute of Earth Sciences, University of Iceland, Sturlugata 7, IS-101 Reykjavík, Iceland [email protected] Abstract — Is Iceland a hotspot, with ridge-centered plume? In Iceland vigorous volcanism has built up a plateau 3.0 km higher than at a normal mid-ocean ridge with 3 to 4 times thicker crust than average oceanic crust. This volcanism can be associated with anomalous volcanism for 56–61 Ma in the form of aseismic ridges that stretch across the North Atlantic Ocean through Iceland, i.e. the Greenland-Iceland-Ridge (GIR) and the Faeroe-Iceland-Ridge (FIR). Iceland is a “meltspot” and an hotspot and the GIR and FIR may be hotspot trails. The trends or age progressions of the GIR and FIR are too uncertain to conclude if the Iceland hotspot can be a fixed reference point. There is a large seismic low-velocity anomaly (LVA) in the mantle under Iceland at least down to 400–450 km depth and with globally low velocities down to ∼200 km depth. The center of the LVA is at 64◦40’N and 18◦10’W between the glaciers Hofsjökull and Vatnajökull. The shape of the LVA is approximately that of a cylinder in the depth range 100–450 km, but at certain depths elongated in the north- south direction. The LVA extends at least up to 30–40 km depth beneath Central Iceland and the rift zones. The shallower part of the LVA (i.e. above ∼150 km depth) extends at least ∼700 km outside of Iceland to the southwest, along the Reykjanes Ridge. The LVA has been numerically modelled with geodynamic methods by several authors as a ridge-centered convecting plume. They try to fit crustal thickness of the Iceland hotspot and neighbouring ridge, and the magnitude and shape of the LVA. The latest of these models find a best fit: A plume 135–150◦C hotter than background mantle, retaining in general 1% partial melt in a maximum ∼90 km thick melting zone, but reaching up to 2–3% partial melt in the shallowest mantle. The rest of produced melt goes into forming the crust. Considerable work has been carried out on various plume models to explain these and other observations in Iceland, but the models are still some way from reaching a mature state. As long as important observations are lacking and some key questions remain unanswered, alternatives to the plume model or more realistic variants of it in a larger tectonic framework, including heterogeneous mantle, should not be discouraged. INTRODUCTION canic activity over much broader regions, i.e. large Hotspot definition igneous provinces. Hotspots place their mark on the plate with a trail of past locations of their volcanism, Hotspots are places with vigorous volcanism over mil- called a hotspot trail or track (aseismic ridge or vol- lions or tens of millions of years. They warm up canic chain). In the oceans larger hotspots build up the crust in their locality. The main volcanic ac- a high plateau over their surroundings, with thicker tivity is confined to a relatively narrow area, usu- crust. Hotspot volcanism is mostly basaltic in the ally under 500 km in diameter, that builds up a re- oceans, but a mix of rhyolite and basalt on the con- gion approximately oval in shape. It is often pro- tinents. Hotspots are here defined as a crustal feature, posed that hotspots may be related to vigorous vol- JÖKULL No. 58, 2008 3 I. Þ. Bjarnason but in the literature their deeper source is sometimes it and 1000 times less viscous than the lower man- also referred to as a hotspot. There is consensus that tle (Steffen, 2007). Hence the general movement of the sources of hotspots are in the mantle, but not of the mantle under the asthenosphere, and lateral move- their actual nature or depth extent. It is even debated ments of plumes should be slower than those of the if hotspots are hot spots at all (Foulger and Anderson, plates. Early on it was realised that not all hotspot 2005), whereas all agree that they are regions of in- sources are fixed with respect to each other although creased melt production, "meltspots". The number of in many cases they do move slower than the plates defined active hotspots has gradually risen to over 40, (Molnar and Atwater, 1973; Molnar and Francheteau, varying in ages from 5–200 Ma (Steinberger, 2000). 1975). There are, however, hotspots which are rel- Hotspot proliferation has been criticised. atively stable with respect to each other. They are The deep plume hotspot-source hypothesis Pacific hotspots called the Hawaii group, Northeast- Atlantic hotspots (the Iceland group) and African, At- The Canadian geoscientist J. Tuzo Wilson (1908– lantic and Indian ocean hotspots (the Tristan group) 1993) first proposed in a number of articles (e.g. (Pilger, 2003; mesoplates in Wikipedia). Through Wilson, 1963) that a hotspot source is deep in the Cenozoic time (since 65 Ma) misfits in hotspot traces mantle and probably moves slower than the overrid- of the Hawaiian (Pacific) group and hotspots in the ing plate (i.e. rheological lithosphere). He suggested Tristan (Indo-Atlantic) group imply relative motion of that hotspot sources provide a fixed reference frame 5–80 mm/yr between the groups, with the lower num- for the plates, and that trends and age progression ber in more recent times (Raymond et al., 2000). A of hotspot trails indicate the absolute motion of the global hotspot-fixed reference frame with respect to plates during geological time. The American geo- the mantle is not as fixed as previously thought, and physicist W. J. Morgan proposed that hotspot sources further research is needed in this field. However, it is are upwellings of hot buoyant rock rising all the way still an important tool together with magnetic stratig- from the lower mantle, and called them "Convection raphy of the oceans for plate reconstruction (i.e. the plumes from the lower mantle" (Morgan, 1971). As history of the movements and changes in the size of the plume material reaches a shallow depth in the the plates). The relative movement of the Iceland mantle it starts to partially melt, because of the high group with respect to the other two large groups is temperature of the plume and the positive relation be- not much reported on in the literature, probably due to tween solidus temperature and pressure (i.e. lowered rather large uncertainties in the hotspot tracks within solidus temperature at lower pressure causing decom- the Iceland group. pression melting). The melt has lower density than the surrounding mantle and percolates upwards. Part Other hotspot-source hypotheses of the melt that reaches the crust rises all the way Anderson (2000), later joined by Foulger (2002), have to the surface, which may supply vigorous volcan- led a vigorous campaign opposing the lower mantle ism; the rest is intruded at depth. With the assump- plume source of hotspots, and even mantle plumes tion that the hotspot sources are fixed in the mantle, in general. They prefer to call hotspots “meltspots”. the absolute motions of the Earth’s plates have been They argue that mid-plate volcanic island chains are calculated from the directions and age progressions loci of maximum strain in the plates, and that heat of several hotspot trails. One of the arguments for in the asthenosphere can vary considerably producing the fixity of plumes relative to the plates comes from shallow “pseudo-plume-like” structures without deep the large difference in viscosity of the different man- thermal instabilities, i.e. small scale convection move- tle layers. The asthenosphere, a relatively thin shal- ments without deep thermal sources. They also argue low zone in the mantle (∼160 km thick on average that the mantle is intrinsically heterogeneous (agreed in the depth range 80–220 km), decouples the plates by many), and hence variably fertile for melt produc- from the rest of the upper mantle. It is approximately tion. Where a fertile mantle and large strain areas 10 times less viscous than the upper mantle beneath in plates coincide, meltspots will form. It follows 4 JÖKULL No. 58, 2008 An Iceland Hotspot Saga that if hotspot sources are confined to the shallow tral Iceland rift system, beneath northwest Vatnajök- low-viscosity asthenosphere then it is unlikely that ull glacier (Sæmundsson, 1979). Later we will see hotspots can provide a mantle-fixed reference frame. that the locus of the hotspot source in the mantle is at ◦ ◦ It seems, at least in theory, that meltspots cannot 64 40’N and 18 10’W, between the glaciers Hofsjök- escape being crustal hot spots unless they are vigor- ull and Vatnajökull. The shape of the volcanic edifice ously cooled. Melt is an efficient transporting medium that the I-hotspot has built in the last ∼25 Ma is oval for bringing heat up towards the surface from the man- with approximately 500 km N-S minor and 800 km E- 2 tle. If small-scale convections in the asthenosphere W major axis, or 0.3 million km in area including the exist that “... give rise to pseudo-plume-like struc- Iceland shelf. The high plateau of Iceland stands ∼3.0 tures...”, a phenomenon that the no-plume advocates km above the -2.3±0.3 km average depth of hotspot- have not excluded (Anderson, 2000), they are in my unaffected young crust farther south in the North At- opinion thermal mantle plumes, only shallow ones. lantic Ocean (Malinverno, 1990). To assess the crustal Other hypotheses for hotspot sources include me- (melt) production in the I-hotspot, it is necessary to teorite impacts, that would provide additional heat know the average crustal thickness in Iceland.
Load more

Recommended publications
  • Volcanic Ash Over Europe During the Eruption of Eyjafjallajökull on Iceland, April–May 2010 In: Atmospheric Environment (2011) Elsevier
    Final Draft of the original manuscript: Langmann, B.; Folch, A.; Hensch, M.; Matthias, V.: Volcanic ash over Europe during the eruption of Eyjafjallajökull on Iceland, April–May 2010 In: Atmospheric Environment (2011) Elsevier DOI: 10.1016/j.atmosenv.2011.03.054 1 Volcanic ash over Europe during the eruption of Eyjafjallajökull on Iceland, 2 April-May 2010 3 4 Baerbel Langmann1), Arnau Folch2), Martin Hensch3) and Volker Matthias4) 5 6 1) Institute of Geophysics, University of Hamburg, KlimaCampus, Hamburg, Germany, 7 e-mail: [email protected] 8 2) Barcelona Supercomputing Center - Centro Nacional de Supercomputación, Barcelona, 9 Spain, e-mail: [email protected] 10 3) Nordic Volcanological Center, University of Iceland, Reykjavik, Iceland, e-mail: 11 [email protected] 12 4) Institute of Coastal Research, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany, 13 e-mail: [email protected] 14 15 Abstract 16 During the eruption of Eyjafjallajökull on Iceland in April/May 2010, air traffic over Europe 17 was repeatedly interrupted because of volcanic ash in the atmosphere. This completely 18 unusual situation in Europe leads to the demand of improved crisis management, e.g. 19 European wide regulations of volcanic ash thresholds and improved forecasts of theses 20 thresholds. However, the quality of the forecast of fine volcanic ash concentrations in the 21 atmosphere depends to a great extent on a realistic description of the erupted mass flux of fine 22 ash particles, which is rather uncertain. Numerous aerosol measurements (ground based and 23 satellite remote sensing, and in situ measurements) all over Europe have tracked the volcanic 24 ash clouds during the eruption of Eyjafjallajökull offering the possibility for an 25 interdisciplinary effort between volcanologists and aerosol researchers to analyse the release 26 and dispersion of fine volcanic ash in order to better understand the needs for realistic 27 volcanic ash forecasts.
    [Show full text]
  • Hot Spots and Plate Movement Exercise
    Name(s) Hot Spots and Plate Movement exercise Two good examples of present-day hot spot volcanism, as derived from mantle plumes beneath crustal plates, are Kilauea, Hawaii (on the Pacific oceanic plate) and Yellowstone (on the continental North American plate). These hot spots have produced a chain of inactive volcanic islands or seamounts on the Pacific plate (Fig. 1) and volcanic calderas or fields on the North American plate (Fig. 2) – see the figures below. Figure 1. Chain of islands and seamounts produced by the Hawaiian hot spot. Figure 2. Chain of volcanic fields produced by the Yellowstone hot spot. The purposes of this exercise are to use locations, ages, and displacements for each of these hot spot chains to determine 1. Absolute movement directions, and 2. Movement rates for both the Pacific and western North American plates, and then to use this information to determine 3. Whether the rates and directions of the movement of these two plates have been the same or different over the past 16 million years. This exercise uses the Pangaea Breakup animation, which is a KML file that runs in the standalone Google Earth application. To download the Pangaea Breakup KML file, go here: http://csmgeo.csm.jmu.edu/Geollab/Whitmeyer/geode/pangaeaBreakup /PangaeaBreakup.kml To download Google Earth for your computer, go here: https://www.google.com/earth/download/ge/agree.html Part 1. Hawaiian Island Chain Load the PangaeaBreakup.kml file in Google Earth. Make sure the time period in the upper right of the screen says “0 Ma” and then select “Hot Spot Volcanos” under “Features” in the Places menu on the left of the screen.
    [Show full text]
  • Iceland Is Cool: an Origin for the Iceland Volcanic Province in the Remelting of Subducted Iapetus Slabs at Normal Mantle Temperatures
    Iceland is cool: An origin for the Iceland volcanic province in the remelting of subducted Iapetus slabs at normal mantle temperatures G. R. Foulger§1 & Don L. Anderson¶ §Department of Geological Sciences, University of Durham, Science Laboratories, South Rd., Durham, DH1 3LE, U.K. ¶California Institute of Technology, Seismological Laboratory, MC 252-21, Pasadena, CA 91125, U. S. A. Abstract The time-progressive volcanic track, high temperatures, and lower-mantle seismic anomaly predicted by the plume hypothesis are not observed in the Iceland region. A model that fits the observations better attributes the enhanced magmatism there to the extraction of melt from a region of upper mantle that is at relatively normal temperature but more fertile than average. The source of this fertility is subducted Iapetus oceanic crust trapped in the Caledonian suture where it is crossed by the mid-Atlantic ridge. The extraction of enhanced volumes of melt at this locality on the spreading ridge has built a zone of unusually thick crust that traverses the whole north Atlantic. Trace amounts of partial melt throughout the upper mantle are a consequence of the more fusible petrology and can explain the seismic anomaly beneath Iceland and the north Atlantic without the need to appeal to very high temperatures. The Iceland region has persistently been characterised by complex jigsaw tectonics involving migrating spreading ridges, microplates, oblique spreading and local variations in the spreading direction. This may result from residual structural complexities in the region, inherited from the Caledonian suture, coupled with the influence of the very thick crust that must rift in order to accommodate spreading-ridge extension.
    [Show full text]
  • Mantle Transition Zone Structure Beneath Northeast Asia from 2-D
    RESEARCH ARTICLE Mantle Transition Zone Structure Beneath Northeast 10.1029/2018JB016642 Asia From 2‐D Triplicated Waveform Modeling: Key Points: • The 2‐D triplicated waveform Implication for a Segmented Stagnant Slab fi ‐ modeling reveals ne scale velocity Yujing Lai1,2 , Ling Chen1,2,3 , Tao Wang4 , and Zhongwen Zhan5 structure of the Pacific stagnant slab • High V /V ratios imply a hydrous p s 1State Key Laboratory of Lithospheric Evolution, Institute of Geology and Geophysics, Chinese Academy of Sciences, and/or carbonated MTZ beneath 2 3 Northeast Asia Beijing, China, College of Earth Sciences, University of Chinese Academy of Sciences, Beijing, China, CAS Center for • A low‐velocity gap is detected within Excellence in Tibetan Plateau Earth Sciences, Beijing, China, 4Institute of Geophysics and Geodynamics, School of Earth the stagnant slab, probably Sciences and Engineering, Nanjing University, Nanjing, China, 5Seismological Laboratory, California Institute of suggesting a deep origin of the Technology, Pasadena, California, USA Changbaishan intraplate volcanism Supporting Information: Abstract The structure of the mantle transition zone (MTZ) in subduction zones is essential for • Supporting Information S1 understanding subduction dynamics in the deep mantle and its surface responses. We constructed the P (Vp) and SH velocity (Vs) structure images of the MTZ beneath Northeast Asia based on two‐dimensional ‐ Correspondence to: (2 D) triplicated waveform modeling. In the upper MTZ, a normal Vp but 2.5% low Vs layer compared with L. Chen and T. Wang, IASP91 are required by the triplication data. In the lower MTZ, our results show a relatively higher‐velocity [email protected]; layer (+2% V and −0.5% V compared to IASP91) with a thickness of ~140 km and length of ~1,200 km [email protected] p s atop the 660‐km discontinuity.
    [Show full text]
  • Oaklands School Geography Department - Iceland Trip 2019
    Oaklands School Geography Department - Iceland Trip 2019 Skogafoss Waterfall Name: __________________________________ Tutor Group: _____________________________ 1 Part A: Where is Iceland? Iceland is an island formerly belonging to Denmark. It has been a Republic since 1944 and is found in the middle of the North Atlantic Ocean. We will fly to Keflavik and stay near Hvolsvollur in the SW of the island. The map above is an enlargement of the box drawn on the map of Iceland below left. Map area on next Clearly, we are only visiting a small section of page the island, but in this small area you will be blown away by what you will see. Perhaps your visit to the island will prompt you to come back to explore further in the future? 2 Part B: History of Iceland Iceland is only about 20 million years old! It was formed by a series of volcanic eruptions at the Mid- Atlantic ridge. In fact the plume of magma called the Iceland ‘Hot Spot’ is responsible for its continued existence and almost continuous volcanic activity. Exact dates for first human occupancy is uncertain, but the accepted date is 874 for the first permanent settlers from Scandinavia. They settled near Reykjavik (which means ‘smokey cove’ – due to the Geothermal heat). Settlers continued to come from Norway, Scotland and Ireland. The first parliament was held at Thingvellir (pictured right), where chieftains met and agreed laws and rules for the country. The country converted to Christianity in the 11th Century, but pagan worship was tolerated if it was in secret. Civil war followed and the end result was that Iceland accepted Norwegian sovereignty and were ruled by the Norwegian kings.
    [Show full text]
  • Cenozoic Changes in Pacific Absolute Plate Motion A
    CENOZOIC CHANGES IN PACIFIC ABSOLUTE PLATE MOTION A THESIS SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAI`I IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN GEOLOGY AND GEOPHYSICS DECEMBER 2003 By Nile Akel Kevis Sterling Thesis Committee: Paul Wessel, Chairperson Loren Kroenke Fred Duennebier We certify that we have read this thesis and that, in our opinion, it is satisfactory in scope and quality as a thesis for the degree of Master of Science in Geology and Geophysics. THESIS COMMITTEE Chairperson ii Abstract Using the polygonal finite rotation method (PFRM) in conjunction with the hotspot- ting technique, a model of Pacific absolute plate motion (APM) from 65 Ma to the present has been created. This model is based primarily on the Hawaiian-Emperor and Louisville hotspot trails but also incorporates the Cobb, Bowie, Kodiak, Foundation, Caroline, Mar- quesas and Pitcairn hotspot trails. Using this model, distinct changes in Pacific APM have been identified at 48, 27, 23, 18, 12 and 6 Ma. These changes are reflected as kinks in the linear trends of Pacific hotspot trails. The sense of motion and timing of a number of circum-Pacific tectonic events appear to be correlated with these changes in Pacific APM. With the model and discussion presented here it is suggested that Pacific hotpots are fixed with respect to one another and with respect to the mantle. If they are moving as some paleomagnetic results suggest, they must be moving coherently in response to large-scale mantle flow. iii List of Tables 4.1 Initial hotspot locations .
    [Show full text]
  • Deep Earth Structure: Lower Mantle and D"
    This article was originally published in Treatise on Geophysics, Second Edition, published by Elsevier, and the attached copy is provided by Elsevier for the author's benefit and for the benefit of the author's institution, for non-commercial research and educational use including without limitation use in instruction at your institution, sending it to specific colleagues who you know, and providing a copy to your institution’s administrator. All other uses, reproduction and distribution, including without limitation commercial reprints, selling or licensing copies or access, or posting on open internet sites, your personal or institution’s website or repository, are prohibited. For exceptions, permission may be sought for such use through Elsevier's permissions site at: http://www.elsevier.com/locate/permissionusematerial Lay T Deep Earth Structure: Lower Mantle and D″. In: Gerald Schubert (editor-in-chief) Treatise on Geophysics, 2nd edition, Vol 1. Oxford: Elsevier; 2015. p. 683-723. Author's personal copy 00 1.22 Deep Earth Structure: Lower Mantle and D T Lay, University of California Santa Cruz, Santa Cruz, CA, USA ã 2015 Elsevier B.V. All rights reserved. 1.22.1 Lower Mantle and D00 Basic Structural Attributes 684 1.22.1.1 Elastic Parameters, Density, and Thermal Structure 684 1.22.1.2 Mineralogical Structure 685 1.22.2 One-Dimensional Lower Mantle Structure 686 1.22.2.1 Body-Wave Travel Time and Slowness Constraints 687 1.22.2.2 Surface-Wave/Normal-Mode Constraints 688 1.22.2.3 Attenuation Structure 688 1.22.3 Three-Dimensional
    [Show full text]
  • Geological Survey of Finland
    Geological Survey of Finland Bulletin 357 Paleoproterozoic volcanism in the Kühtelysvaara - Tohmajärvi district, eastern Finland by Lauri J. Pekkarinen and Heikki Lukkarinen Geologian tutkimuskeskus Espoo 1991 - - ----- --- - - Geological Survey of Finland, Bulletin 357 P ALEOPROTEROZOIC VOLCANISM IN THE KIIHTELYSVAARA - TOHMAJÄRVI DISTRICT, EASTERN FINLAND by LAURI J. PEKKARINEN AND HEIKKI LUKKARINEN with 17 figures, 1 table and 3 appendices GEOLOGIAN TUTKIMUSKESKUS ESPOO 1991 Pekkarinen, L.J. & Lukkarinen, H., 1991. Paleoproterozoie volcanism in the Kiih­ telysvaara - Tohmajärvi distriet, eastern Finland. Geological Survey 0/ Finland, Bulletin 357,30 pages, 17 figures, I table and 3 appendiees. The numerous episodes of Paleoproterozoie volcanism and assoeiated sedimen­ tation preserved in the Kiihtelysvaara - Tohmajärvi distriet represent both prolonged and episodie rifting of eratonie erust. V-Pb zireon age determinations from two mafie dykes intruded in eonjunetion with the basalmost lava flows indieate an age of ca. 2120 - 2100 Ma for this earliest mafie magmatism. However, no informa­ tion is yet available eoneerning the age of the younger flows, dykes or sills. Pyroclastie units are also present and have, along with the mafie lava flows and intrusions, been metamorphosed under greenschist facies eonditions. Volcan­ ism took plaee in an intraeratonie, within-plate setting, with predominantly basal­ tie eompositions. Hydrothermal alteration oeeurred both during and after erup­ tion. This affeeted the chemical composition of the earlier lava in particular, the younger lava flows as weil as the dykes and sills generally showing less evidence of ehemical alteration. The volcanogenic and sedimentary formations of the Kiihtelysvaara area have been renamed according to local geographical place names and regional correla­ tions and comparisons have been made between the study area and similar sequences elsewhere in Finland, particularly with respect to the mafie units.
    [Show full text]
  • Scientific Research of the Sco Countries: Synergy and Integration 上合组织国家的科学研究：协同和一体化
    SCIENTIFIC RESEARCH OF THE SCO COUNTRIES: SYNERGY AND INTEGRATION 上合组织国家的科学研究：协同和一体化 Materials of the Date: International Conference November 19 Beijing, China 2019 上合组织国家的科学研究：协同和一体化 国际会议 参与者的英文报告 International Conference “Scientific research of the SCO countries: synergy and integration” Part 1: Participants’ reports in English 2019年11月19日。中国北京 November 19, 2019. Beijing, PRC Materials of the International Conference “Scientific research of the SCO countries: synergy and integration”. Part 1 - Reports in English (November 19, 2019. Beijing, PRC) ISBN 978-5-905695-74-2 这些会议文集结合了会议的材料 - 研究论文和科学工作 者的论文报告。 它考察了职业化人格的技术和社会学问题。 一些文章涉及人格职业化研究问题的理论和方法论方法和原 则。 作者对所引用的出版物，事实，数字，引用，统计数据，专 有名称和其他信息的准确性负责 These Conference Proceedings combine materials of the conference – research papers and thesis reports of scientific workers. They examines tecnical and sociological issues of research issues. Some articles deal with theoretical and methodological approaches and principles of research questions of personality professionalization. Authors are responsible for the accuracy of cited publications, facts, figures, quotations, statistics, proper names and other information. ISBN 978-5-905695-74-2 © Scientific publishing house Infinity, 2019 © Group of authors, 2019 CONTENTS ECONOMICS 可再生能源发展的现状与前景 Current state and prospects of renewable energy sources development Linnik Vladimir Yurievich, Linnik Yuri Nikolaevich...........................................12 JURISPRUDENCE 法律领域的未命名合同 Unnamed contracts in the legal field Askarov Nosirjon Ibragimovich...........................................................................19
    [Show full text]
  • COURSE NOTES V0
    Sheep in the Land of Fire and Ice Sauðfé í landi elds og ísa COURSE NOTES v0 Sheep in the land of Fire and Ice COURSE NOTES v0 Contents PART 1. COURSE INTRODUCTION SECTION 1.1 SHEEP IN THE LAND OF FIRE AND ICE About this course Meet the experts Navigating the course PART 2. SHEEP GRAZING IN THE NORTH SECTION 2.1 SHEEP GRAZING IN THE NORTH Grazing in Nordic regions Studying herbivory in the North – the need for coordinated research efforts SECTION 2.2 SHEEP GRAZING IN ICELAND Environmental conditions in Iceland How do these conditions influence the impacts of grazing? SECTION 2.3 SHEEP GRAZING CAN LEAD TO SOIL EROSION PART 3. HISTORICAL PERSPECTIVE OF SHEEP GRAZING IN ICELAND SECTION 3.1 ICELAND BEFORE SHEEP What Iceland could have looked like before human settlement SECTION 3.2 MODELLING THE ECOSYSTEM State and transition models SECTION 3.3 THEN, SHEEP ARRIVED Sheep over time: from landnám to our days SECTION 3.4 EFFORTS TO MITIGATE ENVIRONMENTAL DEGRADATION PART 4. THE PRESENT AND THE FUTURE OF SHEEP GRAZING IN ICELAND SECTION 4.1 SHEEP IN ICELAND TODAY Current grazing systems in Iceland SECTION 4.2 CURRENT EFFORTS IN ECOLOGICAL RESEARCH Grazing research SECTION 4.3 SUSTAINABLE SHEEP GRAZING? The future of sheep grazing PART 5. SUMMARY AND CONCLUSIONS SECTION 5.1 SUMMARY AND CONCLUSIONS USEFUL LINKS REFERENCES 2 Sheep in the land of Fire and Ice COURSE NOTES v0 Part 1. Course introduction Section 1.1 Sheep in the Land of Fire and Ice About this course Sheep in the Land of Fire and Ice is a short Massive Open Online Course (MOOC) about sheep grazing in Iceland.
    [Show full text]
  • The Plate Tectonics of Cenozoic SE Asia and the Distribution of Land and Sea
    Cenozoic plate tectonics of SE Asia 99 The plate tectonics of Cenozoic SE Asia and the distribution of land and sea Robert Hall SE Asia Research Group, Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 0EX, UK Email: robert*hall@gl*rhbnc*ac*uk Key words: SE Asia, SW Pacific, plate tectonics, Cenozoic Abstract Introduction A plate tectonic model for the development of SE Asia and For the geologist, SE Asia is one of the most the SW Pacific during the Cenozoic is based on palaeomag- intriguing areas of the Earth$ The mountains of netic data, spreading histories of marginal basins deduced the Alpine-Himalayan belt turn southwards into from ocean floor magnetic anomalies, and interpretation of geological data from the region There are three important Indochina and terminate in a region of continen- periods in regional development: at about 45 Ma, 25 Ma and tal archipelagos, island arcs and small ocean ba- 5 Ma At these times plate boundaries and motions changed, sins$ To the south, west and east the region is probably as a result of major collision events surrounded by island arcs where lithosphere of In the Eocene the collision of India with Asia caused an the Indian and Pacific oceans is being influx of Gondwana plants and animals into Asia Mountain building resulting from the collision led to major changes in subducted at high rates, accompanied by in- habitats, climate, and drainage systems, and promoted dis- tense seismicity and spectacular volcanic activ- persal from Gondwana via India into SE Asia as well
    [Show full text]
  • Azores and Iceland
    13th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 2369 A COMPARATIVE STUDY ON STRONG GROUND MOTION IN TWO VOLCANIC ENVIRONMENTS: AZORES AND ICELAND Carlos S. OLIVEIRA1, Ragnar SIGBJÖRNSSON2, Simon ÓLAFSSON3 SUMMARY The objective of this paper is to present the main results of a comparative study of strong ground motion on the Azores and Iceland. These islands are a super-structural part of the Mid Atlantic Ridge, which marks the boundary between the North-American Plate and the Eurasian Plate and creates a north-south oriented belt of seismic and volcanic activity. The tectonic environments are described and compared emphasising the similarities in the geological structure, including surface geology and its effects on strong ground motion. Furthermore, the seismicity of the Azores and Iceland is compared based on earthquake catalogues using statistical analysis. The strong-motion networks on the islands are described along with the strong-motion data used in the subsequent analysis. The strong-motion data are compared using statistical analysis. The main emphasis is put on attenuation of strong-motion data, characterised by root mean square acceleration and peak ground acceleration. The attenuation is also compared to some of the common attenuation relationships, used by the engineering community in Europe and America. The main findings are that there are significant similarities between the tectonic environments of the Azores and Iceland. Furthermore, the similarities found in seismicity are statistically significant. The attenuation is characterised by rapid decay with increasing distance and high acceleration in the near source area. It is found that the same ground motion estimation models can be applied on the Azores and in Iceland.
    [Show full text]