Glacier Effects of the M7.9 Denali Fault Earthquake of November 3, 2002

Avalanches cover 13 sq. km. of lower Black Rapids Glacier. Photo on Nov. 7, 2002 by R. March, USGS.

On November 3, 2002 a magnitude 7.9 earthquake struck the Denali Fault in central Alaska. It was the largest earthquake in the United States since 1986 and ties for the 9th largest earthquake in the United States in the last 200 years (top 15 list). The earthquake ruptured 260 kilometers of the Denali Fault with measured offsets as much as 8 meters as of this writing. The fault is of interest to glaciologists because 130 kilometers, or about half, of the rupture lies under glaciers. The fault rupture crosses the West Fork, Susitna, Black Rapids, Canwell, Gakona, Chistochina, and numerous smaller glaciers.

November 7 Flight Observations

Double fault trace running down upper West Fork Chistochina Glacier. Photo on Nov. 7, 2002 by R. March, USGS.

On November 7, 2002 Dennis Trabant and Rod March (US Geological Survey, Fairbanks, AK), and Dr. Martin Truffer (University of Alaska, Geophysical Institute, Fairbanks, AK) flew by fixed wing Cessna 206 to document the effects of the Nov. 3, 2002 magnitude 7.9 Denali Fault earthquake. We were able to fly and photograph the fault trench from near Cantwell to just NW of Mentasta Lake and additionally south of the fault trench between the Richardson Highway and Susitna Glacier to observe the areas around Eureka, Maclaren, and East Fork Glaciers. The north flank of the central and eastern Alaska Range was obscured by clouds and was not investigated. Deep shadows due to low sun angles made some areas difficult to see and photograph. Features observed and photographed included numerous rock, snow, and ice avalanches, single linear faults, sub-parallel linear fault pairs, shear zones with multiple sub parallel faults, long curved faults that appear to follow glacial structures, zigzag faults, at least one significant fault perhaps 1 km south of the Denali Fault that was not parallel to the Denali Fault trench, odd looking holes on a glacier surface along the main fault that may be surrounded by blast debris, avalanche-debris dammed lakes both on and off glaciers, numerous small glacier surficial lakes that had drained, cracking in lake ice, glacier cracks that indicate drainage of subglacial lakes (these may be pre-quake features), dark rims around lakes that may have been evidence of seiches. The most dramatic features by far were the very large, mostly rock avalanches onto Black Rapids and the very large glacier collapse/avalanche onto Gakona Glacier.

Map and Photo galleries arranged by 8 regions along the fault rupture.

Detailed chronological description of flight observations.

Reports

Truffer, M., Craw, P., Trabant, D., 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 [abstract and poster]