HR: 15:25h
AN: V52E-08    [PDF]
TI: Towards a 4D Viscoelastic Model for Deformation of the Long Valley Caldera 1997 Inflation Episode
AU: * Newman, A V
EM: anewman@lanl.gov
AF: Earth and Environmental Sciences, EES-9 Los Alamos National Laboratory, MS 462, Los Alamos, NM 87544
AU: Dixon, T H
EM: tdixon@rsmas.miami.edu
AF: RSMAS-MGG, University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149
AU: Gourmelen, N
EM: ngourmelen@rsmas.miami.edu
AF: RSMAS-MGG, University of Miami, 4600 Rickenbacker Cswy., Miami, FL 33149
AB: We investigate the effects of viscoelastic rheologies and non-spheroidal sources on time-dependent deformation for a large silicic volcanic body. We focus on surface deformation at Long Valley caldera for the 1997 inflationary episode, but the methods developed here should apply to similar systems elsewhere. We begin with the model in Newman et al. (J. Volc. Geoth. Res., 2001), a spherical magma chamber encased by a 1-km thick viscoelastic shell ($\mu = 5$ GPa, $\nu = 0.25$, $\eta = 10^{16}$ Pa-s -- similar to a 600 degree rhyolite at 5% wt. water) in an elastic half-space ($\mu = 5$ GPa, $\nu = 0.25$) and extend it to include ellipsoidal geometries that better represent magmatic sources. The data include 2-color EDM baselines, 3-D continuous GPS, and temporally limited but spatially dense synthetic aperture radar interferograms. All models fit a source at similar location and depth to the inflation source identified by Langbein et al. (JGR, 1995) for the 1989 inflation episode, indicating the source has not migrated significantly in that 8 year period. Though this technique is unable to uniquely identify the source volume, allowing for significant uncertainty in magma pressure changes, all models that include a modest (500 m thick) viscoelastic shell require only a fraction of the pressure required by purely elastic models ($\sim$20-70 MPa rather than 400$+$ MPa). This is significant because the lithostatic load at 6 km depth is only $\sim$160 MPa and magma pressures that far exceed it would predict eruption.
DE: 1236 Rheology of the lithosphere and mantle (8160)
DE: 8145 Physics of magma and magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting