HR: 15:35h
AN: V14A-01 INVITED     [Abstracts]
TI: Volcano-ice Interaction Under Glaciers, Interplay of ice Rheology, Volcano Construction and Subglacial Hydrology
AU: * Gudmundsson, M T
EM: mtg@hi.is
AF: Institute of Earth Sciences, University of Iceland Sturlugata 7, Reykjav¡k, IS-101 Iceland
AU: Sigmundsson, F
EM: fs@hi.is
AF: NORVOL, Institute of Earth Sciences, University of Iceland Sturlugata 7, Reykjav¡k, IS-101 Iceland
AU: Bjornsson, H
EM: hb@raunvis.hi.is
AF: Institute of Earth Sciences, University of Iceland Sturlugata 7, Reykjav¡k, IS-101 Iceland
AU: Hognadottir, T
EM: disah@raunvis.hi.is
AF: Institute of Earth Sciences, University of Iceland Sturlugata 7, Reykjav¡k, IS-101 Iceland
AB: Eruptions under temperate glaciers can be complicated events, controlled by the interplay between ice thickness, surface and bedrock geometry, hydrological conditions at the base, eruption rate and magma composition. However, the most important characteristic is rapid melting of ice during extremly fast heat exchange from magma to ice. Usually this occurs with almost simultaneous subglacial drainage of the meltwater. Ice thickness seems to be a controlling factor in determining the rheological response of a glacier in a volcanic eruption. Where the glacier is thin (100-200 m or less) it responds to the rapid deformation rates caused by melting and drainage mainly with brittle fracturing, leading to rapid penetration of the glacier and subaerial phreatomagmatic eruption. Where the ice is several hundred meters thick, ductile deformation appears to be dominant, leading to rapid inflow of ice towards the eruption site. In this case the rate of melting is controlled by the eruption rate. The best-studied eruption of this type was Gjalp, Iceland, in 1996. At Gjalp, basal water pressure at the vents was 3-6 MPa during early phases of the eruption and all indications suggest that activity was explosive. The buildup of the 6-km long NNE-SSW trending edifice under the glacier modified the subglacial hydraulic regime which in turn influenced the form of the edifice. The southern and central parts of the edifice are steep and narrow as a consequence of ice confinement; water pressure was always much lower than glaciostatic. In the northern part, where the water pressure may have exceeded glaciostatic, the edifice is low and wide, suggesting only minimal confinement by ice. Removal of subglacially-erupted tephra by meltwater was relatively minor at Gjalp. However, where conditions are favourable, a large part of the tephra may be flushed from the eruption site. This tephra may eventually be deposited outside the glacier, on outwash plains or in the ocean.
DE: 1827 Glaciology (1863)
DE: 1863 Snow and ice (1827)
DE: 8414 Eruption mechanisms
DE: 8424 Hydrothermal systems (8135)
DE: 8429 Lava rheology and morphology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly