Eldfjallafræði flæðibasaltsyrpa frá míósen á Austfjörðum

Included in the supplementary files are seven photogrammetric panels and one geological map (1:100 000) of eastern Iceland.Flood basalt groups in the Neogene lava piles of eastern Iceland are subject to investigation. The groups form the stratigraphic section above the Reyðarfjörður central volcano up to the Thingmuli central volcano, mapped by the British geologist G. P. L. Walker and his students in the 1950s and 60s. The groups were chosen as representative of the three predominant basalt types in Iceland, namely the Hólmar and Grjótá olivine basalt groups, the Kumlafell, Hólmatindur and Hjálmadalur aphyric basalt groups (mostly tholeiitic) and the Grænavatn porphyritic basalt group. Ground mapping and aerial photogrammetry were applied to assess the facies architecture of the groups, map their extent and distribution, measure the thickness of the lava flows and log the internal structure of representative flows. The source origin of each group was identified and the mode of emplacement of the flow types assessed with constraints on effusion rates. A new tectono-magmatic model for scale, geometry and evolution of the Neogene rift systems and mantle anomaly in Iceland is put forward, building on structural volcanological and geochemical evidence.Í jarðlagastafla Austfjarða eru mjög víðáttumiklar hraunlagasyrpur sem myndast hafa í miklum flæðigosum á míósen. Sex syrpur voru rannsakaðar en þær liggja í staflanum á milli megineldstöðva sem kenndar eru við Reyðarfjörð og Þingmúla. Syrpurnar endurspegla meginflokka íslenskra basalthrauna samkvæmt feltskiptingu G. P. L. Walkers, sem kortlagði þær ásamt samstarfsmönnum sínum upp úr miðri síðustu öld. Hólmasyrpa og Grjótársyrpa eru úr ólivínbasalti, Kumlafellssyrpa, Hólmatindssyrpa og Hjálmadalssyrpa að mestu úr dílalitlum hraunum af þóleiískri gerð en Grænavatnssyrpan að mestu úr dílabasalti. Uppbygging hraunlagasyrpanna var könnuð með nákvæmri loftljósmyndun. Þá var innri gerð hraunlaganna athuguð og henni lýst með aðferðum eðlisrænnar eldfjallafræði og strúktúrjarðfræði. Bergsýni úr dæmigerðum hraunlögum voru efnagreind, bæði aðal- og snefilefni. Í kjölfarið var upprunasvæði hraunsyrpanna áætlað, flæðiferli hraunanna lýst og kvikustreymi úr gosrás við myndun þeirra áætlað. Þessar athuganir og aðrar hafa leitt til framsetningar nýs líkans um stærð, lögun og þróun rekbeltisins og möttulstróksins á Íslandi á míósen, en það býður upp á mögulegar úrlausnir á gömlum þrætueplum í túlkun á jarðfræði Íslands.The Ph.D. project was funded by Nordic Volcanological Center - NORDVULK, and the Icelandic Centre for Research - RANNÍS (granted to Morten S. Riishuus, grant number 130529-051)

The Skerin ridge on Eyjafjallajökull, south Iceland: Morphology and magma-ice interaction in an ice-confined silicic fissure eruption

Skerin ridge is a 4.5 km long and on average 100 m wide ridge, situated on a radial fissure trending NW from the summit caldera of the ice-capped central volcano Eyjafjallajökull, south Iceland. Results from previous studies on tephrochronological dating of deposits produced by jokulhlaups originating in the Skerin area indicate that the ridge was formed by an intraglacial (or within glacier) eruption in the 10th century. Recent glacial recession has exposed the Skerin ridge and thus enabled a detailed examination of the ridge structure and architecture, in particular features that indicate confinement and rapid cooling by meltwaters as expected for lava-ice interaction. In this study, the ridge and associated formations were mapped in detail, the petrographic and chemical characteristics documented and the thickness of ice surrounding the ridge measured with a mobile radio-echo sounder. Skerin ridge is primarily constructed by trachytic lavas (volume ~0.043 km3) but also includes lesser mafic (basaltic icelandite/hawaiite) and intermediate (trachyandesite) tephra deposits (volume ~0.012 km3). Lithostratigraphy correlations indicate that the initial stage of the Skerin eruption was marked by a basaltic eruption creating a scoria cone on the NW end of the ice-free fissure with a phreatomagmatic eruption of same composition creating a tuff deposit on the SE ice-covered section of the fissure. At synchronous time an explosive eruption took place forming pumice deposits followed by an effusive eruption of trachyte lavas from a row of vents along the volcanic fissure. The lavas confined by wet cavities and canyons in the thin ice (~100 m) formed a marginal carapace of glassy columnar joints representing the area cooled by the meltwaters and a brecciated flow top being the subaerial expression of the flow as the lavas broke through the glacier. A massive microcrystalline flow interior with flow structures and fabrics formed within the crust typical for lavas cooled within an insulated environment. The eruption ended with a strombolian phase forming scoria deposits of intermediate composition on top of the trachyte lavas. Evidence is for at least one previous eruption episode to Skerin ridge of unknown age forming a glacio-confined lava flow field of basaltic composition north of the ridge. Petrographic examination shows that the erupted magma features numerous examples of disequilibrium textures confirming that magma mixing/mingling took place shortly before onset of eruption in which the silicic eruption appears to have been triggered by a mafic intrusion. The eruption products plot on the transitional line of the alkali versus silica diagram which is a characteristic trend for the south Iceland flank zone. The products and related eruption styles at Skerin ridge provide important data for paleo-ice thicknesses as well as constraints on ice melting rates. Volume constrains on ice melting and the application of a simple modeling of meltwater generation gave meltwater volumes of 500-2500 m3/s for the initial phreatomagmatic phase (<2 hrs) and 10-100 m3/s for the effusive phase (5 to 50 days). Thus an eruption of this type although not large demands precaution by civil protection authorities since flooding may cause hazard for e.g. popular tourist routes and farmland by Markarfljót.Viðlagatrygging Ísland

Volume, effusion rate, and lava transport during the 2021 Fagradalsfjall eruption: Results from near real‐time photogrammetric monitoring

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