HR: 14:55h
AN: G13C-06    [Abstracts]
TI: Will Present day Glacier Retreat Cause Increased Volcanic Activity? Stress and its Effect on Magmatism induced by Glacier Retreat after the Little Ice Age at the Vatnajökull ice cap, Iceland
AU: * Pagli, C
EM: carolina.pagli@uni.lu
AF: Faculty of Sciences, Technology and Communication, University of Luxembourg, 162a, Avenue de la Faienceire, Luxembourg, L-1511, Luxembourg
AU: Sigmundsson, F
EM: fs@hi.is
AF: Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Sturlugata 7, Reykjavik, 101, Iceland
AB: Global warming causes retreat of ice cap and ice sheets. Can melting glaciers trigger higher frequency of magmatic events? During the deglaciation of Iceland, at the Pleistocene-Holocene boundary, eruption rate is inferred to have been about 30-100 times its steady state. Increased decompressional mantle melting due to ice removal has been suggested as the main cause of the increase in melt production during deglaciation. A similar situation, on a smaller scale, exists in Iceland today. Since 1890 glaciers in Iceland have been continuously retreating, with the largest mass decrease occurring at the Vatnajökull ice cap. Ice melting is inducing crustal deformation around the ice cap with vertical velocities up to 25 mm/yr. We investigate the possible interactions between ongoing glacio-isostasy and an eventual change in melting rate or eruptive activity at volcanoes underneath Vatnajökull. A recent study of the glacio-isostatic deformation due to ice volume reduction at Vatnajökull since 1890 indicates a viscosity of the lower crust and upper mantle between 4- 10x10¹⁸ Pa s, assuming an elastic plate thickness of 10-20 km. Using these rheological parameters and a model of the ice retreat, we calculate the rate of change of pressure in the melting region. This pressure decrease is about 2x10^-6 GPa/yr, which is an order of magnitude smaller than the rate of change of pressure decrease during deglaciation (about 1.9x10^-5 GPa/yr). However, the current pressure decrease corresponds to moving the melting column upward by ~6 cm/yr. Stress changes also occur in the elastic layer, concentrating at the edges of the ice cap. Stretching of the crust, reducing pressure up to about -0.01 MPa/yr, takes place in the uppermost 5 km, while crustal compression of about 0.003 MPa/yr occurs between 5 and 10 km depth. These stresses are lower than those caused by stretching over the plate spreading region in Iceland (0.01-0.004 MPa/yr) but are likely to modulate the volcanic activity underneath Vatnajökull. The volcano most affected by these processes is the Bárdarbunga volcano, which is located at the ice cap edge. This volcanic system is inferred to have a deep magma chamber in the ductile layer probably connected to a shallow crustal magma chamber through a system of conduits. Glacio-isostatic stresses in the area may be such that both the deep and shallow magma chambers are subject to pressure decrease thus facilitating accommodation of residing magma, while compression of the conduits would prevent magma migration between the magma chambers. In this model current glacio-isostatic stress changes may reduce likelihood of volcanic activity at Bárdarbunga.
DE: 1622 Earth system modeling (1225)
DE: 8164 Stresses: crust and lithosphere
DE: 8488 Volcanic hazards and risks
SC: Geodesy [G]
MN: 2007 Fall Meeting