Influence of surface load variations on eruption likelihood: application to two Icelandic subglacial volcanoes, Grímsvötn and Katla

• Published in: Geophysical Journal International
• Main Authors: Albino, F., Pinel, V., Sigmundsson, F.
• Other Authors: Laboratoire de Géophysique Interne et Tectonophysique (LGIT), Observatoire des Sciences de l'Univers de Grenoble (OSUG), Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut polytechnique de Grenoble - Grenoble Institute of Technology (Grenoble INP )-Institut national des sciences de l'Univers (INSU - CNRS)-Institut national de recherche en sciences et technologies pour l'environnement et l'agriculture (IRSTEA)-Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS)-Laboratoire Central des Ponts et Chaussées (LCPC)-Institut de Recherche pour le Développement (IRD)-Centre National de la Recherche Scientifique (CNRS), Nordic Volcanological Center, Institute of Earth Sciences, Institute of Earth Sciences University of Iceland, University of Iceland Reykjavik -University of Iceland Reykjavik
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2010
• Subjects: Numerical solutions; Mechanics; Magma chamber processes; [SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology; Ice cap; Katla; Mýrdalsjökull
• Online Access: https://insu.hal.science/insu-00543303; https://insu.hal.science/insu-00543303/document; https://insu.hal.science/insu-00543303/file/ark%20_67375_HXZ-WT09DSXZ-W.pdf; https://doi.org/10.1111/J.1365-246X.2010.04603.X

International audience We investigate how surface load variations around volcanoes act on shallow magma chambers. Numerical calculations are carried out in axisymmetric geometry for an elliptical chamber embedded in an elastic medium. Magma compressibility is taken into account. For variable chamber shape, size and depth, we quantify how unloading events induce magmatic pressure change as well as variation of the threshold pressure required for dyke initiation at the chamber wall. We evaluate the triggering effect of these surface events on onset of eruptions and find it depends strongly on the surface load location and the magma chamber shape. We apply this model to two active Icelandic subglacial volcanoes: Grímsvötn and Katla. The 2004 eruption of Grímsvötn was immediately preceded by a jökulhlaup, a glacial outburst flood of 0.5km3. We show that this event may have triggered the eruption only if the system was very close to failure conditions. Katla volcano is covered by the Mýrdalsjökull ice cap. An annual cycle, with up to 6m change in snow thickness, occurs from winter to summer. As the seasonal snow load is reduced, a pressure decrease of the same order of magnitude as the load is induced within the magma storage zone. Our model predicts that, in the case of a spherical or horizontally elongated magma chamber, eruptions are more likely when the snow cover is smallest, which appears consistent with the fact that all the last nine major historical eruptions at Katla occurred during the summer period. The model predicts an increase in Coulomb stress around the caldera, up to 7km from its centre, during unloading periods, enough to trigger earthquakes. Stress due to snow load variations, with focusing of it in weak zones near the caldera boundary, is considered a contributing factor to seasonal seismicity observed beneath Mýrdalsjökull.