HR: 0800h
AN: C41A-0046    [Abstracts]
TI: Seismic and Glaciological Implications of the 2001 Tsar Mountain Rockslide on a Clemenceau Icefield Group Cirque Glacier, BC, Canada
AU: * Jiskoot, H
EM: hester.jiskoot@uleth.ca
AF: Department of Geography, University of Lethbridge, Lethbridge, AB T1K 3M4, Canada
AB: A long runout rockslide off the south ridge of Tsar Mountain was detected on a Clemenceau Icefield Group cirque glacier. The size, morphology, sedimentology, timing, and possible mechanisms for this rockslide were determined using satellite imaging and airborne photography in combination with analysis of seismic data and automatic snow pillow climate data. Seismic waveform data for the region suggest that several large mass wasting events might have taken place on nearby glaciers over the past 30 years. The Tsar rockslide has a rhomboidal shape with prominent levees around the perimeter. With a length of 1.3 km, footprint area of 1.37 km², an estimated volume of 1 x 10⁷ m³, and a fahrböschung of 13.8° (tan 0.24), it is within the expected range of values for catastrophic rockslides on other glaciers. Slide debris ranges from sand and pebble size to boulders with diameters up to 25 m. The larger clasts appear concentrated on, or close to, the levees and some reverse grading was observed. Sediment thickness varies from 30 m in the levees to an estimated 1-10 m at the centre. No disturbance of the glacier surface or its overridden medial moraines can be detected, suggesting limited interaction between the base of the slide and the substrate. The rockslide covers 24% of the cirque glacier, but the mass balance effects might be limited because of the pre- existing debris cover. However, an increase in basal shear stress from the addition of mass might have resulted in an acceleration of the glacier. Satellite imaging narrowed down the timing of the rockslide between 9 July and 11 August 2001. Of the 13 seismic events recorded within this period, only one had its epicentre close to the cirque, suggesting that the event took place on 13 July 2001 at 18:09 local time. This coincides with the end of winter snowmelt, night-time freezing after a week of high temperatures, and a precipitation event in the order of 20 mm/day. Twenty-two similar shallow seismic events occurred between 1986 and 2007, of which two in the rockslide cirque, and five on the neighbouring Shackleton Glacier. Even though not all of these mass wasting events result in long runout rockslides, a glacier's sediment yield will be significantly affected by this intermittent supraglacial sediment supply.
DE: 0720 Glaciers
DE: 0758 Remote sensing
DE: 1810 Debris flow and landslides
DE: 7215 Earthquake source observations (1240)
SC: Cryosphere [C]
MN: 2007 Fall Meeting