Snow-ice-tephra-lava interactions during the 2010 Fimmvorduhals eruption
Abstract
On March 20th a small basaltic fissure opened at the northern edge of Fimmvorduhals, a popular hiking pass between Eyjafjallajökull, to the west, and Myrdalsjökull, to the east. Immediately prior to the eruption, the vent area was covered with typically 1-3 meters of snow and locally snow-covered, isolated remnants of glacial ice. Fieldwork conducted during June and July documented evidence for a variety of different types of interactions between volcanism (tephra and lava) and snow/ice, including direct contact (e.g. ash-covered snow, lava blocks on snow/ice, lava flows on ash-covered snow), indirect melting (e.g. arcuate snow/ice melting patterns at lava flow fronts, partly collapsed sheet lava flows), and the formation of small bomb-cored mounds via post-depositional snow melting. Many of these features are likely ephemeral, and may leave no trace in the geological record; however under certain circumstances they may leave subtle clues that could aide in identifying the presence of snow during eruptions. The field relationships documented are consistent with varied mechanisms of heat transfer during the eruption to the surrounding environment. The arcuate-shaped snow and ice-banks at the edges of flows appear to closely mimic the shape of the adjacent lava lobes. The geometric relationships are consistent with snow/ice melting several meters in front of the advancing flows by radiant heat from the front of the lava lobes. Also, in at least two areas we observed features that are consistent with snow melting beneath lava, possibly by slower heat conduction. One example is a small cave beneath the lava at the lava-snow contact. The other is a ~1 m thick sheet flow that has partly collapsed, forming a fracture that appears to have been controlled by incipient polygonal jointing; melting of underlying snow may have undermined part of the sheet flow based and facilitated its collapse. However, under at least two separate types of conditions lava seems to have little impact on snow/ice. Firstly, where lava flows onto the coarse apron of lapilli generated during the early part of the eruption, the lapilli layer (~13 cm thick) appears to have insulated the snow and prevented it from melting noticeably. Secondly, towards the distal ends of the flows, blocks of lava were heaved onto bounding snow/ice without producing noticeable melting. The bomb-cored mounds, which are the most evocative structures formed by tephra-snow interactions, are also probably the least likely to be preserved. The mounds appear to have formed by a complex sequence of events, and their stratigraphy, from bottom to top, is: snow, icy-snow, volcanic bomb, coarse black lapilli, and medium- to fine, greenish-gray ash. The mounds appear to record melting and deflation of the snow surface sometime after the deposition of the ash layer, which probably originated from the summit vent at Eyjafjallajökull.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMNH11B1130H
- Keywords:
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- 0799 CRYOSPHERE / General or miscellaneous;
- 8408 VOLCANOLOGY / Volcano/climate interactions;
- 8425 VOLCANOLOGY / Effusive volcanism