Alaska glacier separates – From a Glaciers Perspective

Cordova Glacier retreat and glacier separation revealed by Landsat images from 1987 and 2018, red arrow is the 1987 terminus position of main glacier and tributaries, yellow arrow is the 2018 terminus location. Purple dots indicate the snowline and the pink arrow the former location of Rude Lake.

Cordova Glacier is located at the head of the western fork of the Rude River in the Chugach Mountains, Alaska. In USGS maps the glacier dams Rude Lake which is ~1.5 km long and 0.5 wide (see below). Molnia (2008) noted the lake was gone in 2008 and the former bed was covered by vegetation indicating the lake had not recently drained for the last time. Here we examine changes in the glacier from 1987-2018 using Landsat imagery.

In the USGS map of the region from the 1950’s, Rude Lake is dammed by the terminus of Cordova Glacier, pink arrow. There is a significant tributary entering from the southwest a short distance above the terminus. By 1987 Rude Lake has drained and much of the lake bottom has been occupied by vegetation. The terminus does still extend to the bottom of the West Branch Rude River Valley. The tributary entering from the southwest has detached from Cordova Glacier. The snowline is at 950 m in August 1987. In 9/2016 and 8/2017 the transient snowline is at 1400 m and 1350 m respectively. The former southwest tributary like the main glacier has limited retained snowcover that cannot maintain the glacier at it current size. In early September 2018 the snowline on Cordova Glacier is again at 1400 m. The main terminus has retreated 800 m since 1987. The southwest tributary has both a western and eastern terminus that have retreated 1100 m and 500 m respectively. The total length of the southwest tributary declined from 6.1 km to 4.1 km in length the entire valley reach of the glacier has lost snowpack in 2016-2018. That heralds that this section of the glacier will melt away.

The retreat of this glacier is less significant than many glaciers in the region including Alsek Glacier and Shoup Glacier. The high snowline in 2018 indicative of high ablation, which was also noted on Lowell Glacier.

Alaska Topographic Map of Cordova Glacier indicating Rude Lake, pink arrow.

Cordova Glacier terminus position and snowline revealed by Landsat images from 2016 and 2017, red arrow is the 1987 terminus position of main glacier and tributaries, yellow arrow is the 2018 terminus location. Purple dots indicate the snowline and the pink arrow the former location of Rude Lake.

Fasset Glacier in 1987 and 2016 Landsat images. Red arrow indicates glacier front in 1987, pink arrows indicates areas where glacier retreat has exposed rock/bare ground and purple dots indicate snowline.

Fasset Glacier drains west from The Brabazon Range near Yakutat and had terminated in Tanis Lake for the entire 20th century. (Truessel et al 2013) and Truessel et al (2015) note the rapid retreat and thinning of nearby Yakutat Glacier. Here we examine Landsat imagery that illustrates the retreat from 1987 to 2016.

The glacier extended most the way to the southern end of the Tanis Lake in the 1951 Yakutat map. In 1987 the glacier terminated on the northeast shore of Tanis Lake. The calving front in the lake was 800 m wide. The snowline was at 600 m. In mid-June of 2014 the snowline was already at 600 m, by the end of the melt season it was at 900 m. In 2016 the terminus of the glacier no longer reaches Tanis Lake. The eastern side of the terminus is stagnant and ends 200 m from the shore of the lake. The western edge terminates in a new lake that is forming. The average retreat has been 250 m for the glacier from 1987-2016. The larger changes are upglacier of the terminus where large areas of bedrock have been exposed due to retreat, and several segments of the glacier that used to be joined have separated. The snowline is at 850 m in 2016. There are three large areas of bedrock denoted in the 2014 Google Earth image below. The two at 500 m well above the terminus appeared as medial moraines in 1987 and are now bedrock ridges 600 m and 1100 m long. There is a group of ogives extending below these two locations indicating the annual flow rate is 100 m/year in this reach of the glacier. The new lake is also evident in the Google Earth image.

Walker Glacier, Yakutat Glacier and East Novatak Glacier are nearby glaciers that have experienced greater recent retreat than Fasset Glacier. Fasset Glacier is poised to continue a moderate rate of retreat.