HR: 0800h
AN: V51D-0775    [Abstracts]
TI: Ground Tilt Associated with the 2004-Present Eruption of Mount St. Helens, Washington
AU: * Anderson, K
EM: kander@stanford.edu
AF: Stanford University, 397 Panama Mall, Stanford, CA 94305, United States
AU: Lisowski, M
EM: mlisowski@usgs.gov
AF: Cascades Volcano Observatory, 1300 SE Cardinal Court, Suite 100, Vancouver, WA 98683, United States
AU: Segall, P
EM: segall@stanford.edu
AF: Stanford University, 397 Panama Mall, Stanford, CA 94305, United States
AB: Tiltmeters in the near-vent region of effusively erupting volcanoes may shed important light on the mechanics of lava extrusion and dome growth. Tiltmeters installed in the crater at Mount St. Helens, Washington, during the ongoing eruption (2004 to present) have recorded cyclic, repeating tilt events throughout the course of the eruption. Individual tilt events last from minutes to hours, are remarkably coherent between different tiltmeters within the crater, and frequently display a clear saw-tooth shaped temporal evolution. Azimuths of the tilt events have remained remarkably consistent over time, and point to a source located generally beneath the south part of the 1980-86 lava dome. Local seismic activity strongly affects the tilt signals, introducing both an instrument response unrelated to real ground tilt, and also in many cases triggering real tilt events that may last for many minutes. Teleseisms are easily detected by the tiltmeters, and have also been observed to trigger longer-period tilt events. It seems likely that ground tilt is related to the motion of (nearly solid) magma as it moves up the conduit at Mount St. Helens, and its diversion to the south beneath the 1980-86 lava dome. While the eruption appears to be steady over longer time scales, the tilt signals require episodic behavior. Inversion of the tilt data for a generalized source should reveal the kinematics of this transient process.
DE: 8419 Volcano monitoring (7280)
DE: 8425 Effusive volcanism
DE: 8499 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting