November 23, 2014

South Sheep River Glacier Retreat, Alaska

Posted by Mauri Pelto

South Sheep River Glacier is the informal name of the longest glacier in the Talkeetna Mountains of Alaska. This glacier is the headwaters of the Sheep River and is comprised of two major glacier branches from the east and west meeting and turning north down the Sheep River valley. Molnia (2007) noted that all glaciers in the region have retreated since the early 1950’s when the area was mapped. Molnia (2007) noted that all the major termini were retreating and thinning in 2000. Here we examine Landsat imagery from 1986 to 2014. In the early 1950’s the glacier extended 5.5 km north down the Sheep River Valley from the main glacier junction, red arrow.
sheep river glacier map
In each image the red arrow indicates the early 1950 terminus position, the yellow arrow the 1986 terminus and the pink arrow the 2014 terminus position. In 1986 the glacier had retreated 2.5 km from the 1950’s position. The terminus is at the mouth of the first significant glacier valley draining into the Sheep River from the west. The medial moraine extending to the terminus from the glacier junction is quite prominent. There is a small tributary at Point A that joins the eastern branch of the glacier. In 1989 the snowline on the glacier is at 1700 m. By 2001 the glacier has retreated substantially from the yellow arrow and side valley from the west. In 2009 the snowline is quite high at 2000 m. Th eastern tributary is quite thin beyond the junction, and adds little ice to the now short northward flowing segment. The late Sept. 2014 Landsat image is after a fall snowstorm and the snowline has lowered. The terminus is now at the pink arrow a 4.5 km retreat since the early 1950’s. The glacier has retreated 2 kilometers since 1986. The tributary at Point A now terminates 600 meters from the eastern branch. The glacier flows just 1 km north from the main junction versus 5.5 km in 1950. The terminus remains thin, and the narrow eastern tributary appears ready to separate from the west flowing tributary. This is not an imminent change, but is inevitable. The retreat is the same as that of nearby Sovereign Glacier and glaciers to the south, Pedersen Glacier and Fourpeaked Glacier
sheep river glacier 1986
1986 Landsat image

sheep river glacier 1989
1989 Landsat image

sheep river glacier 2001
2001 Landsat image

sheep river glacier 2009
2009 Landsat image

sheep river glacier 2014
2014 Landsat image