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Effects of the M7.9 Denali Fault Earthquake on glaciers in the Alaska
Range
by Truffer, M., Craw, P., Trabant, D., and March, R.
ABSTRACT
Glaciers are present in many valleys aligned with the Denali fault. As a
result, more than 40% of the surface rupture resulting from the November 3, 2002 M7.9 event is
on glaciers. Surface rupture was observed on the Susitna, Black Rapids, Canwell, Gakona, and
Chistochina Glaciers. In addition, offset glacier ice was observed near the terminus of the
West Fork Glacier where the Susitna Glacier fault (SGF), a newly discovered fault, intersects
the glacier.
Offsets resulting from the Denali Fault earthquake in glacial ice have
variable morphologies. The earthquake epicenter was located near an icefall in a tributary of
the West Fork Glacier. Almost all seracs in the icefall toppled during the event. The Denali
fault laterally offset pre-existing crevasses on the north side of the Canwell Glacier and
vertical offset was observed at many localities. At some locations, one or more long linear
cracks can be traced along the glacier surface, often following moraines that presumably form
areas of weakness. The SGF appears to make a sharp turn to the west where it follows a looped
moraine across the glacier. At some locations along the Denali fault cracks in the ice are
oriented perpendicular to the fault trace. These observations suggest that careful
examination of glacier morphology must be considered while delineating fault traces in
glaciers.
The most dramatic changes to glaciers resulted from rock, ice and snow
avalanches released by the earthquake. Three rock falls from the south wall of the Black
Rapids Glacier cover about 13 km of the ablation area or about 5% of the total glacier area.
The blanketing effect of these rock falls will increase the glacier's mass balance by about
0.2 ma -1
by insulating the ice from warm summer temperatures. A large rock and ice fall also
occurred on the upper Gakona Glacier. The rock and ice fall will not affect the glacier's mass
balance immediately, because it was deposited onto the glacier's accumulation area. These rock
falls will be a readily visible surface feature for the next 200 to 400 or more years. Prior
to the November 3 event, large rock and ice fall debris cover was not evident on the glaciers
of the region. This suggests that an event of similar consequences has not occurred in the
recent past.
Truffer, M., Craw, P., Trabant, D., and March, R. , Effects of the M7.9 Denali Fault
Earthquake on glaciers in the Alaska Range, Eos Trans. AGU, 83(47), Fall Meet. Suppl.,
Abstract S72F-1334
Poster
 [Full Poster, Acrobat PDF (1.3MB)]
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Maintainer: Rod March
Last update:
Wednesday, January 03, 2007 12:46 PM
URL: http://ak.water.usgs.gov/glaciology/m7.9_quake/reports/2002agu_poster/index.
htm |
