HR: 0800h
AN: C51A-0261    [Abstracts]
TI: Iceberg calving at Rapidly Retreating Tidewater Glacier: Columbia Glacier, AK, USA.
AU: McNamara, D E
EM: mcnamara@usgs.gov
AF: U.S.G.S., National Earthquake Information Center, Golden, CO 80401 United States
AU: * O'Neel, S
EM: shad@colorado.edu
AF: Univ. CO Boulder INSTAAR, 1560 30th st., Boulder, CO 80303 United States
AU: Marshall, H
EM: marshalh@colorado.edu
AF: Univ. CO Boulder INSTAAR, 1560 30th st., Boulder, CO 80303 United States
AU: Pfeffer, T
EM: pfeffer@tintin.colorado.edu
AF: Univ. CO Boulder INSTAAR, 1560 30th st., Boulder, CO 80303 United States
AB: An array of eleven seismometers including one broadband instrument was deployed around the lower Columbia Glacier margin during June 2004 for a period one year. This network recorded small local seismic events (icequakes) and four explosions detonated in boreholes on the glacier. Additionally, we documented changes in glacier geometry with a single time lapse camera. For 25 days we made detailed observations of iceberg calving, noting the time of calving events along with the location and size of the event. Ice motion was measured with GPS 7 km upstream from the terminus for 60 days and within 1 km of the terminus for 25 days using optical methods. Waveforms from the broadband sensor are used to characterize seismic signals originating from calving events. Calving events produce seismic signals which have a 1-3 Hz characteristic frequency, and non-impulsive onsets. Submarine events often contain an additional low frequency component that is not present during sub-aerial events. We use motion and photogrammetric measurements to explore the relationship between calving and ice motion and also between calving and near-terminus glacier geometry.
DE: 0720 Glaciers
SC: Cryosphere [C]
MN: Fall Meeting 2005