HR: 1340h
AN: V53C-1428    [Abstracts]
TI: Influence of surface load variations on the monitoring and behaviour of a volcanic system: Application to Katla subglacial volcano, Iceland.
AU: * Pinel, V
EM: Virginie.Pinel@univ-savoie.fr
AF: LGIT-Universite de Savoie, Campus Scientifique, Le Bourget du Lac, 73376, France, Metropolitan
AU: Sigmundsson, F
EM: fs@hi.is
AF: Nordic Volcanological Center, Institute of Earth Science, Askja, University of Iceland Sturlugata 7, Reykjavik, IS-101, Iceland
AU: Sturkell, E
EM: sturkell@hi.is
AF: Nordic Volcanological Center, Institute of Earth Science, Askja, University of Iceland Sturlugata 7, Reykjavik, IS-101, Iceland
AU: Geirsson, H
EM: dori@vedur.is
AF: Icelandic Meteorological Office, Bustadavegur 9, Reykjavik, 150, Iceland
AU: Einarsson, P
EM: palli@hi.is
AF: Institute of Earth Science, Askja, University of Iceland Sturlugata 7, Reykjavik, IS-101, Iceland
AU: Gudmundsson, M T
EM: mtg@hi.is
AF: Institute of Earth Science, Askja, University of Iceland Sturlugata 7, Reykjavik, IS-101, Iceland
AU: Albino, F
EM: tom.fabien@wanadoo.fr
AF: LGIT-Universite de Savoie, Campus Scientifique, Le Bourget du Lac, 73376, France, Metropolitan
AB: Surface mass redistribution in the vicinity of volcanoes is a common process. Many volcanoes are covered by ice cap or glaciers which thickness evolves through time because of climate warming or seasonal effects. However most of changes of surface load are even directly linked to the volcano activity. The eruptive products contribute to the building of the edifice: a few millions m³ dome may rise in several months. Stress changes induced by mass redistribution can even be more important in case the edifice gets partially destroyed during the eruptive event. Such load variations around a volcanic edifice act both to induce a surface deformation signal and to produce pressure changes inside and around the storage zone. In a perspective of risk assessment, this deformation signal has to be discriminated from the effect of magma displacement at depth. Besides pressure changes act in turn to change failure conditions and exsolved gas content. We calculated the displacement induced by the variation of the Mýrdalsjökull ice cap thickness, Iceland, where an annual cycle in ice load occurs as well as a gradual ice retreat as a consequence of climate warming. Seasonal vertical displacements measured from 2000 to 2006 at two continuous GPS stations located near the edge of Mýrdalsjökull ice cap fit well to a model of an elastic response to the annual variation in ice load. A comparison of model displacements and observations provides a minimum value of 29 ± 5 GPa for the effective static local value of the Young's modulus. We infer long-term displacements induced compared to GPS measurements used to monitor the Katla volcano lying beneath the Mýrdalsjökull ice cap. A forward model considering an elastic thickness of 5 km can explain a fraction of the uplift recorded from 1999 to 2004, but it cannot account for the observed horizontal velocities. The study confirms that magma inflow is required to explain observed inflation of the Katla volcano 1999-2004. We, then, estimate the pressure change induced inside a magma storage zone by seasonal and long-term ice load variations. Results show that the seasonal effect can induce pressure changes of the order of 0.3 bar inside an underlying magma chamber.
DE: 7218 Lithosphere (1236)
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8419 Volcano monitoring (7280)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting