September 27, 2022

Tebenkof Glacier, Alaska Snowcover Loss Exposes Century of Annual Layers

Posted by Mauri Pelto

Tebenkof Glacier in 2018 ESRI World Image with annual layers numbered. from near the divide to near the terminus. A couple of layers of layers buried near top of glacier by snowcover. This indicates 90-100 annual layers exposed at the surface as they emerge at the surface.

Tebenkof Glacier is a land terminating glacier on the Kenai Peninsula just west of Blackstone Bay. WGMS (2021) documented the retreat rate from 1910-2009 as ~20 m/year. Black and Kurtis (2022) examined 19 tidewater glaciers on the Kenia Peninsula identifying a 42 km² area loss from 1984-2021.  From 1986-2022 Landsat imagery indicates a retreat of 1100 m. During the summers of 2018-2020 the glacier lost all or nearly all snowpack, this allowed atellite imagery to reveal ~90-100 annual layers exposed from divide to near the terminus during years when the glacier was stripped of snowpack such as in 2018-2020.

Tebenkof Glacier retreat from 1986-2022 generating proglacial lake as it retreated 1100 m.

Tebenkof Glacier has an unsually low elevation and consistent gentle slope with the main glacier divide at 650 m and terminus at 200 m, with a length of 9 km. From 650 m where the first annual line layer is visible to 275 m where the last annual layer is visible is a distance of 6.5 km, with an average slope of 3.3 degrees. Above the equilbrium annual layers are submergent and below this line annual layers are emergent.The observed velocity at the blue and orange X show a remarkable consistency just as the slope with the 2017-2021 average fron the NASA ITS_LIVE of 60.72 at the orange point and 60.68 m/year at the blue x. This translates to travel time of 100 years from the divide to the end of the annual layer area. This is slightly more than the number of visible annual layers, however a few years have had no retained accumulation and hence no layer would form.

Tebenkof Glacier in Landsat images in 2018 and 2020 with less than 2% retained snowcover exposing annual layers.

Tebenkof Glacier velocity data at two locations, both averaging 60 m/year, velocity from NASA ITS_LIVE