July 15, 2021
Sheridan Glacier, Alaska Retreat Causes Rapid Lake Expansion
Posted by Mauri Pelto
Sheridan Glacier in 2002 and 2020 Landsat images illustrating retreat of the margin and expansion of the lake. Red arrow is 2002 margin on small island, yellow arrow is 2020 terminus location just north of Sherman Glacier stream and purple dots are the snowline.
Sheridan Glacier in the Chugach Mountains of Alaska begins at 1500 m and flow southwest out of the mountains with the terminus spreading out in a lake basin on the low slope coastal plain. Sheridan Lake is a proglacial lake at the terminus that drains into the Sheridan River which 12 km later reaches tidewater. From 1950 to 2000 Sheridan Glacier experienced modest retreat, with the terminus, with a fringing proglacial Sheridan Lake persisting, followed by a terminus disintegration from2000-2016. (Shugar et al 2018). Here we examine Landsat imagery from 2002-2020 to identify the retreat and resultant lake expansion.
In 2002 the proglacial lake has an area of 3.8 km2, with the terminus crossing one small island in the lake. The snowline is at 750 m. In 2013 there is a 4 km2 terminus area that has disintegrated, the terminus has retreated off of the island. The snowline is at 850 m. By 2016 the terminus has retreated north of the glacier stream from Sherman Glacier entering from the east, though much of the lake is still filled with an iceberg melange. The snowline is at 925 m. In 2020 the Sheridan Lake area has expanded to 11.2 km2, representing a retreat of 7.4 km2 since 2002. The snowline in 202o is at 970 m. In June 2021 there are a significant number of new icebergs indicating ongoing lake expansion during 2021. Sheridan Lake is not a large glacial lake by Alaskan standards, but is bigger than any glacial lake in most alpine regions such as the Himalaya. The ability to be so large is in large part due to the ability to develop larger basin on low sloped terrain near the coastline.
The amount of terminus retreat here is less than that at Excelsior Glacier or Yakutat Glacier, but the lake expansion rate is comparable to Excelsior Glacier.
Sheridan Glacier in 2013 and 2016 Landsat images illustrating the breakup of a large terminus region generating a melange of icebergs. Red arrow is 2002 margin on small island, yellow arrow is 2020 terminus location just north of Sherman Glacier stream and purple dots are the snowline.
June 2021 Sentinel Image indicating considerable new iceberg activity leading to ongoing lake expansion in 2021.