HR: 10:50h
AN: G52A-03    [Abstracts]
TI: Surface deformation associated with the 2004-2005 eruption of Mount St. Helens
AU: * Lisowski, m
EM: mlisowski@usgs.gov
AF: USGS Cascades Volcano Observatory, 1300 SE Cardinal Court, Building 10, Suite 100, Vancouver, wa 98683 United States
AU: Dzurisin, D
EM:
AF: USGS Cascades Volcano Observatory, 1300 SE Cardinal Court, Building 10, Suite 100, Vancouver, wa 98683 United States
AU: Iwatsubo, E
EM:
AF: USGS Cascades Volcano Observatory, 1300 SE Cardinal Court, Building 10, Suite 100, Vancouver, wa 98683 United States
AU: LaHusen, R
EM:
AF: USGS Cascades Volcano Observatory, 1300 SE Cardinal Court, Building 10, Suite 100, Vancouver, wa 98683 United States
AB: The eruption of a new lava dome in the crater of Mount St. Helens has been accompanied by slow inward collapse (< 20 mm/yr) and subsidence (<30 mm/yr) at continuous GPS stations (CGPS) located within 15 km of the volcano. No anomalous premonitory deformation was observed in a 50-station network of campaign GPS stations surveyed in 2000 and 2003 nor in the displacement of a CGPS station (JRO1, located 8.5 km to NNW) operating since 1999. Anomalous movement of JRO1 towards Mount St. Helens began at the same time as the initial seismic swarm (September 23, 2004), and slowed following a series of phreatic explosions in early October. Recovery of 7 campaign GPS stations on the volcanic edifice showed no measurable deformation between 2003 and early October 2004. By mid-October 2004, a network of 9 CGPS stations (5 USGS, 4 Plate Boundary Observatory) was installed to monitor ongoing volcanic deformation. Three more PBO CGPS stations were added by November 2004 and two more in February 2005. Average station velocities from October 17, 2004, to May 21, 2005, are consistent with deflation of a spherical magma chamber (volume loss of ~0.016 cubic km) at a depth of about 13 km. Deformation within the crater and growth of the lava dome are tracked with single-frequency GPS stations slung into place with a helicopter. Observed station displacements are small (mm/day) except near or on the growing lava dome, where they are as much as several meters per day. A borehole tiltmeter (1 s sampling) was installed 400 m from the active vent in early August 2005 to track short-term crater deformation. Growth of the dome is accompanied by episodes of slow inflation and deflation (up to several microradians) that last for days and earthquakes that produce small tilt offsets (< 1 microradian) that are slowly recovered in tens of seconds to minutes.
DE: 1200 GEODESY AND GRAVITY
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 7280 Volcano seismology (8419)
DE: 8400 VOLCANOLOGY
DE: 8488 Volcanic hazards and risks
SC: Geodesy [G]
MN: Fall Meeting 2005