HR: 11:35h
AN: V42A-06    [Abstracts]
TI: Co-eruptive Strain Changes and Constraints on Magma Reservoir Incompressibility: Examples from Hekla and Montserrat
AU: * Linde, A T
EM: linde@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, United States
AU: Sacks, I S
EM: sacks@dtm.ciw.edu
AF: Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road NW, Washington, DC 20015, United States
AU: Sturkell, E
EM: sturkell@hi.is
AF: Nordic Volcanological Center, University of Iceland, Sturlugata 7, Askja, Reykjavík, 101, Iceland
AU: Hidayat, D
EM: hidayat@geosc.psu.edu
AF: College of Earth and Mineral Sciences,Penn. State University, 334A Deike Bldg., University Park, PA 16802, United States
AB: Borehole strainmeters have the capability of providing continuous (50 sps) monitoring of deformation with a sensitivity that, for durations up to many days, is much greater than any other measurement type currently available (e.g. roughly 1000 times that for GPS observations). Thus, by installing small arrays of such instruments close enough to an active volcano, it is possible to record deformation due to subsurface magma movement. We examine here data recorded during the 2000 eruption of Hekla, Iceland and a small explosion at Soufriere Hills, Montserrat. In both cases a small network of Sacks-Evertson borehole dilatometers recorded strain changes before and following the surface manifestation of the activity; from these changes we constrain the subsurface geometry of the magmatic system including the reservoir and conduit or dike that forms to connect the reservoir to the surface. Additionally, for the interval preceding surface release of material, we can apply conservation rules for a closed system: we use the relation dV/V= -dP/K (dV is volume change, V is volume, dP pressure change, K is incompressibility). From the data we can estimate values for the dike (or conduit) volume which is also (assuming constant density) the change in reservoir volume and the product dP*V for the reservoir. This allows calculation of the bulk modulus (more correctly a lower limit). Our results indicate that for Montserrat the bulk modulus of the reservoir is quite low (implying a few volume percent of gaseous phases); for Hekla the modulus is very high implying a gas poor (free?) reservoir.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 8428 Explosive volcanism
DE: 8434 Magma migration and fragmentation
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2007 Joint Assembly