HR: 1340h
AN: V53D-1593    [Abstracts]
TI: Deformation at Mount St. Helens from InSAR: What Can We Learn From RADARSAT and ENVISAT Results?
AU: * Poland, M P
EM: mpoland@usgs.gov
AF: USGS, Hawaiian Volcano Observatory P.O. Box 51, Hawaii National Park, HI 96718-0051 United States
AU: Lu, Z
EM: lu@usgs.gov
AF: USGS, National Center for Earth Resources, Observation and Science, Sioux Falls, SD 57198 United States
AB: In late September 2004, seismic unrest signaled the onset of a new eruptive episode at Mount St. Helens, Washington. GPS campaigns conducted in 2000 and 2003 and continuous GPS monitoring from a site located 8 km north of the volcano at Johnston Ridge (JRO1) showed no apparent precursory deformation. However, the motion of JRO1 changed in late September 2004, coincident with the onset of seismicity, and the site has translated towards the crater of Mount St. Helens by over 2 cm since that time. Additional continuous GPS instruments installed by the Cascades Volcano Observatory and Plate Boundary Observatory after the eruption began have also shown horizontal displacements directed radially towards the volcano's crater. This pattern of deformation is consistent with broad deflation of the volcano, probably due to volume loss at depth as magma in a subsurface reservoir is removed by eruption. InSAR has proven to be an ideal tool for imaging the spatial complexities associated with the ongoing eruption of Mount St. Helens. Preliminary results from both RADARSAT and ENVISAT interferograms generated before the eruption show no deformation, supporting the pre-eruptive GPS results. ENVISAT interferograms that span at least several months of the eruption indicate axisymmetric subsidence of the volcano. However, co-eruptive, InSAR-derived displacements are of the same magnitude as topography-correlated atmospheric effects that have been observed in pre-eruptive interferograms. To determine the displacement field at Mount St. Helens from InSAR, we will combine numerous interferograms from both RADARSAT and ENVISAT SAR imagery to minimize the contribution of atmosphere to the apparent displacements. This will include both stacking and time series analysis to measure co-eruptive line-of-sight displacements. Modeling of results, especially when combined with GPS data covering the same time periods, should be helpful in constraining the geometry and history of the deflation source.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
DE: 8419 Volcano monitoring (7280)
DE: 8434 Magma migration and fragmentation
DE: 8485 Remote sensing of volcanoes
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005