January 2, 2011

Thiel Glacier Alaska ongoing retreat

Posted by Mauri Pelto

Thiel Glacier is a valley glacier in the Juneau icefield of Alaska. The glacier was a tributary of the Gilkey Glacier and is shown as such in USGS maps. From 1948-2005 the glacier has retreated 2100 meters from its former junction with the Gilkey Glacier. Below is the USGS map of the area showing the junction of the Battle, Gilkey and Thiel Glacier. The same view from the 2005 Google Earth imagery indicates the separation of the three glaciers and the emergence of a new deglaciated valley section. In 1984 looking down at the glacier from its highest elevation, it was clear that the glacier had too small of an accumulation area to support the long, low elevation valley tongue of the glacier. From that vantage I could not see the terminus. The snowline at the end of the summer typically is at 4000-4500 feet at the end of the melt season, leaving only 45% of the glacier in the accumulation zone. For a glacier to be in equilibrium at least 60% of the glacier needs to be in the accumulation zone. The upper margin of the glacier is outlined in blue and the snowline indicated with blue arrows in the image below. The current glacier terminus is stagnant and the retreat is ongoing. At the terminus a close examination of the 2005 imagery forth indicates a series of concentric crevasses at the terminus. Such crevasses typically are the indicative of a collapse feature. Usually it is a subglacial lake that drains that had supported the terminus to some extent. Above this point the ice is stagnant lacking tranverse crevasses that would indicate movement. The surface of the glacier has a rough cross profile as a result without active movement to even out the profile. Areas of debris generally are prominent as the debris is insulating the ice underneath. The 2005 terminus is at 650 feet, compared to the same location in the USGS maps of 1500 feet. This nearly 900 feet of thinning is depicted by the surface wall overlay added to Google Earth, the top of this wall is at 1500 feet. In the foreground is the Gilkey Glacier which the Thiel formerly joined and the new deglaciated valley. This glacier will continue to retreat rapidly with the current climate much like the nearby Hoboe Glacier and Tulsequah Glacier and Lemon Glacier