Park, M., Clark, D. and Caplan-Auerbach, J., 2010, Ground penetrating radar survey of the ice-filled active crater of Mount Baker, Washington Abstract C33C-0530 presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec.

Ground penetrating radar survey of the ice-filled active crater of Mount Baker, Washington Abstract C33C-0530 presented at 2010 Fall Meeting, AGU, San Francisco, Calif., 13-17 Dec.

Sherman Crater, the center of volcanic activity at Mount Baker, in northwest Washington, provides an excellent site to study glacier dynamics in an active crater because of its history of sudden, significant increases in geothermal activity, its confined geometry, the potential hazards it poses to downstream reservoirs, and the paucity of recent research related to these hazards. We present results from a ground penetrating radar (GPR) survey of the crater conducted in the summers of 2009 and 2010, including characterization of the subglacial crater morphology, estimates for the crater glacierís volume, maximum depth, annual mass balance and surface velocity and for the craterís geothermal flux density. We used a GSSI SIR-3000 GPR system and a low frequency (80 MHz) antenna in common-offset (reflection) collection mode to image subglacial conditions along several west-east and south-north transects within the crater. We processed the GPR data with GSSIís RADAN 6.0 and paired the surface elevations of each transect to the ice-surface topography using GPS locations and spot altimeter readings. GPR profiles reveal several sets of distinct basal and englacial reflectors. Along west-east (longitudinal) transects, the craterís bedrock topography largely follows the glacierís surface (high to the west, descending to the east), but the ice thins dramatically along the margin nearest the crater rimís eastern breach. The prominent basal reflectors in the GPR transects are consistent with an ice/hydrothermally altered rock interface, but short more well-defined segments suggest the presence of bedrock (towards the center of the crater) and water (near the eastern breach) at the base of the ice. GPR data combined with surface ice melting measurements yield a first-order estimate for the area-averaged accumulation rate of 4.8 +/- 0.1 m yr-1 and ablation rate of 2.4 +/- 0.3 m yr-1 water equivalent from surface melting. The resulting calculated geothermal flux for Sherman Crater of ~20 Wm-2 is consistent with published calculations for active calderas (Mt. Veniaminof) and volcanic lakes. We estimate the maximum ice thickness to be ~50 m, and the ice velocity to range from ~3 to 4 m/month during the summer months. Highest surface ice velocities are found on moderate slopes above the deepest part of the crater, where the ice is thickest (inferred from GPR profiles).