77th Annual Meeting of the Southeastern Section of the APS
Volume 55, Number 10
Wednesday–Saturday, October 20–23, 2010;
Baton Rouge, Louisiana
Session BA: The Role of Physics in Atmospheric, Ocean, and Earth Sciences
8:30 AM–10:30 AM,
Thursday, October 21, 2010
Nicholson Hall
Room: 119
Chair: Solomon Bililign, North Carolina A&T University
Abstract ID: BAPS.2010.SES.BA.4
Abstract: BA.00004 : Exploring the interior of an active volcano with deformation models
10:00 AM–10:30 AM
Preview Abstract
Abstract
Author:
Timothy Masterlark
(The University of Alabama)
The migration of restless magma within an active volcano produces a
deformation signature at the Earth's surface. The internal
structure of a
volcano and specific movements of the magma control the actual
deformation
that we observe. Data from radar satellites can map this
deformation for an
entire volcanic system and ground-based seismic instruments can
image the
internal structure. Deformation models simulate this internal
structure,
subjected to the forces of magma movements, and provide the
quantitative
linkage between the observed surface deformation and the
movements of magma
at depth. Satellite radar data indicate that Okmok volcano,
Alaska, subsided
more than a meter during its eruption in 1997. The deformation
pattern
suggests magma extraction from a shallow reservoir. New seismic
tomography
reveals two weak zones within Okmok. The shallow weak zone
corresponds to a
region of fluid-saturated rock that extends from the caldera
surface to a
depth of 2 km. The deep weak zone indicates the presence of the
magma
chamber at a depth of about 4 km. We construct finite element
models (FEMs)
to simulate deformation caused by magma extraction from a chamber
that is
surrounded by a viscoelastic rind of country rock. Thermal models
define the
brittle-ductile transition and thickness of the viscoelastic
rind. This
assemblage, which represents the deep weak zone, is embedded in
an elastic
model domain that includes a shallow weak zone filling the
caldera. Because
the predicted surface deformation is the combined elastic and
viscous
response to magma extraction, these viscoelastic FEMs reduce the
required
magma chamber depressurization (compared to strictly elastic
models) to
within lithostatic constraints, while simultaneously predicting the
magnitude and pattern of deformation observed with satellite
radar data.
More precisely, the satellite radar data are best predicted by an
FEM
simulating a rind viscosity of 7.5$\times $10$^{16}$ Pa$\cdot $s
and a magma
flux of -4.2$\times $10$^{9}$ kg/d from the magma chamber.
Additionally,
the shallow weak zone provides a co-eruption stress regime and
neutral
buoyancy horizon that support lateral magma propagation from the
central
magma reservoir to the observed lava extrusion near the rim of
the caldera.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2010.SES.BA.4