The Alsek Glacier is a large glacier draining into Alsek Lake and the Alsek River. The first glacier upriver of Alsek Glacier flowing from the east and ending on the Alsek River valley floor is an unnamed glacier, here named North Alsek Glacier. The USGS topographic map compiled from a 1958 aerial image indicates a piedmont lobe spread out on the Alsek River lowland, without a lake, and a series of moraine ridges between the glacier terminus and the Alsek River. This glacier drains a series of peaks of 2000 m in elevation and drains directly west toward the Alsek River, blue arrows indicate glacier flow.
USGS map indicating no lake at end of glacier.
Here we examine Landsat imagery to identify the change in terminus position of the glacier from 1984-2013. In 1984 a small lake has developed along the north shore of the lake that is 1000 m by 500 m. The glacier has retreated to a newly exposed knob, possilby and island, at the red arrow. The red arrow in each image indicates the location of this knob, the yellow arrow indicates the 2013 terminus location on the south side of the glacier near the end of a peninsula. There is no lake downglacier of the yellow arrow in 1984. By 2011 the glacier retreat has led to development of a substantial lake that is 2.5 km north to south and 1.1 to 1.5 km side from east to west. In 2013 the central tongue of the glacier has continued to thin and breakup. The northern margin has retreated 2300 m from 1958 to 2013, the central margin 1500 m and the southern margin 1400 m. The majority of the retreat at the northern margin occurred between 1958-1984, while nearly all the retreat occurred after 1984 for the central and southern portion of the glacier. The glacier will continue to retreat out of the lake basin. The retreat has been nearly identical to nearby Walker Glacier that also had a piedmont lobe, but less than the nearby East Novatak Glacier and Yakutat Glacier.
1984 Landsat image
2011 Landsat image
2013 Landsat image
Google Earth image from 2007
Walker Glacier terminates adjacent to the Alsek River, a popular rafting river route. Many rafting trips visit Walker Glacier since it is close to river, has a low slope and few crevasses.
Google Earth Image
In 1984 the glacier ended as a piedmont lobe separated from the river by meters. Today the terminus has retreated into a lake basin at the terminus. Here we examine Landsat imagery from 1984, 2011 and 2013 to identify retreat and lake development. In 1984 there is no lake at the terminus, red dots indicate glacier margin. The terminus particularly on the northwest side is debris covered. The yellow and red arrows indicate locations where the terminus is in 2013 and where new lakes have developed. The pink arrow indicates the end of a tributary that has fed the Walker Glacier. By 2004 the Google Earth imagery indicates a lake that is 400 m wide and 1500 m long. By 2011 the lake on the north side of the terminus is well developed, yellow arrow, but on the west side of the terminus no lake exists, red arrow. By 2013 the new lake is 750 m wide and 1800 m long. The glacier has retreated 800 m since 1984 on the north side, yellow arrow. A narrow lake has now developed on the west side. The combination of lakes indicates that the entire terminus lobe in the lake basin will soon be lost. The terminus remains quite debris covered, has a gentle slope and is relatively uncrevassed; hence, it is stagnant and will collapse-melt away. The last image is from Colorado River & Trail Expeditions , that shows low glacier slope looking north across new lake. This is similar to the collapse of glacier termini in proglacial lakes such as nearby East Novatak Glacier, Grand Plateau Glacier and Yakutat Glacier.
1984 Landsat image
2011 Landsat image
2013 Landsat image
Google Earth image from 2004
Colorado River & Trail Expeditions image-note low glacier slope looking north across new lake.
Novatak Glacier and a large unnamed south-flowing glacier to the east, here designated as East Novatak Glacier, were connected when first mapped by the International Border Commission in the 1906-08 period. By the 1950’s maps indicated the Novatak and East Novatak Glacier have separated, with a lake (A) developing between them. Here we examined 1984-2013 Landsat images to determined changes over the last 30 years.
Map of East Novatak Glacier area.
Google Earth image
East Novatak Glacier ended in a lake (B) in 1984, this lake then drained a short distance south to the Alsek River. The glacier was separated from the main Novatak Glacier by 3.5 km. In each image the 1984 terminus is marked by red arrow and 2013 image by yellow arrow, N marks the location of a nunatak that develops after 1984. In 1987 glacier retreat has connected the northern and southern half of B Lake. Lake A is still getting glacier runoff leading to a lighter blue color. By 2010 A Lake is no longer getting much glacier runoff and the water color is much darker than B Lake. A nunatak has emerged as well due to thinning ice. East Novatak Glacier has retreated out of the lake basin on the low lying plain, and into the mountain valley. In 2013 the terminus has narrowed and has retreated 2.5 to 3 km since 1984. The glacier is now separated from the retreating Novatak Glacier by 6 km. The tributary that used to connect to the main glacier and is partly obscured by the red arrow, now ends well short of the East Novatak Glacier. Most of the East Novatak Glacier is below 1000 m in elevation, which has been the recent snowline elevation. The retreat of this glacier like that of nearby Yakutat Glacier, indicates how suscpetible the Alaskan glaciers in the region with lower elevation accumulation zones are to our warming climate (Truessel et al, 2013). The retreat is similar to Grand Plateau Glacier, but that glacier does have high elevation accumulation areas, that will allow that glacier to survive.