HR: 15:45h
AN: V34A-02    [Abstracts]
TI: Inferences on Volcano Behaviour and Erupted Volume Based on Times Series of Surface Deformation: Limitations and Physical Models.
AU: * Pinel, V M
EM: Virginie.Pinel@univ-savoie.fr
AF: LGIT-Universite de Savoie, Campus Scientifique 73376 Le Bourget du Lac Cedex Tel (33) 4 79 75 86 51 Fax (33) 4 79 75 94 06, Le Bourget du Lac, 73376 France
AB: New spaced based deformation data have greatly improved the monitoring of volcanoes. Times series of surface deformation that span different eruptive episodes are now available for several stratovolcanoes and show cycles of inflation induced by magma accumulation at small depth (<10 km). Shallow storage zones are fed by replenishment from deeper sources and deformation data provide an insight inside the plumbing system. However in term of risk management,a direct comparison between the level of surface deformation currently observed and the one recorded just before the preceding eruption is not a sufficient information to make any prediction for the timing and amplitude of the next event to occur. One reason for this, is that conditions for rock failure and eruption initiation may change drastically from one eruptive cycle to another mainly because of the mass repartition changes induced by the eruption itself. 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: several km³ were removed in a few seconds on May 1980 at Mount St Helens. 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. These pressure changes act in turn to change failure conditions and exsolved gas content. Variation in exsolved gas content modifies magma compressibility which may induce variations in the time of quiescent between two consecutive eruptions and the volume of eruptive products. We present some analytical and numerical models for pressure changes and surface deformation induced by magma chamber replenishment and withdrawal during an eruptive cycle. We then estimate perturbations induced by a sudden partial destruction of the volcanic edifice. Different volatiles contents are investigated. We show how these calculations can be used as a guideline to interpret deformation data in order to constrain both the geometry and pressure conditions of the plumbing system and improve hazard assessment.
DE: 1560 Time variations--secular and long term
DE: 1734 Seismology
DE: 8419 Eruption monitoring (7280)
DE: 8434 Magma migration
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2005 Joint Assembly