Taku Glacier, near Juneau, was a tidewater glacier until the 1940s when it created and overrode a terminal moraine above sea level, ending calving. It advanced at higher rates than most tidewater glaciers until 1988, when its terminus stopped advancing. This advance is unusual in that most of the surrounding glaciers draining the same icefield have retreated. Critical to the understanding of this tidewater glacier’s dynamics is knowledge of its thickness and depth below sea level (BSL).

During the summer of 1993, we measured the depth along several transverse cross sections of Taku Glacier using seismic reflection techniques, in cooperation with the Alaska Department of Natural Resources (DNR-DGGS). Seismic methods were needed because the expected depths were beyond the range of ice radar equipment. The results show that Taku Glacier is the thickest temperate ice yet measured. The maximum thickness is 1477 m, placing the base of the glacier over 600 m BSL. These data were combined with previous thickness measurements to create a longitudinal cross section running the entire length of the glacier. This cross section shows that the glacier fills a 40 km long fjord.

What is perhaps most significant about these depths is the fact that Taku Glacier’s last retreat, which began about 1750, ended over 25 km from the fjord’s head where the bed was over 300 m BSL. This is unusual for tidewater glaciers in Alaska, which typically retreat until reaching shallow water near the head of their fjords. As our seismic depth measurements are separated by many kilometers, it is possible that an undetected bedrock ridge exists between our measurements which could have acted as a pinning point during the last retreat.

Alaska DNR Department of Geological and Geophysical Surveys Grant ???? and NFS Grant OPP91-22783: Scientific personnel; Matt Nolan, Keith Echelmeyer, Chris Larsen, and Roman Motyka (Alaska DNR-DGGS).