Ellsworth Glacier, Alaska Calves Major Iceberg in 2020

On September 23, 2020April 23, 2024 By mspeltoIn alaska glacier retreat2 Comments

Ellsworth Glacier in Landsat images from 2018, 2019 and 2020. Red arrow is the 2016 terminus location, yellow arrow is the 2020 termins location, pink arrow is the rift, purple dots is the snowline, iceberg is Point A. Glacier retreated 2.4 km, main iceberg 1 km²

Ellsworth Glacier is a valley glacier draining south from Sargent Icefield on the Kenai Peninsula in Alaska. Along with the Excelsior Glacier it has been the longest glacier of the icefield. The glacier retreated into an expanding proglacial lake in the early 20th century (USGS-Molnia, 2008). The terminus in 2000 was reported to be 3.5 to 4.5 km from the 1908 position (USGS-Molnia, 2008). In a previous post we examined Landsat images from 1989-2016 to identify the changes including a 500 m retreat on the east margin of the lake and a 3400 m retreat on the west margin. It as noted that “this rapid lake expansion indicates that the lower 3 km of the glacier occupies a basin that will become a lake and that the tongue is partially afloat and given the narrowing thinning tongue is poised for collapse”. Here we document that collapse with Landsat images from 2016-2020.

In 2016 the snowline is at 975 m, the lake has now extended 3 km along the western edge. The terminus is just east of a former tributary glacier, red arrow. The number of icebergs in 2016 indicates that significant ice calved during that year. The retreat of the eastern margin has been 500 m, with a 3.4 km retreat on the west margin. The main tongue in the lower two kilometers is 800 m wide versus 1200 m wide in 1989. In 2018 the snowline is at 1100 m, the terminus remains just west of a former tributary glacier. There is a rift forming near the pink arrow, where an iceberg will eventually detach (A). In late June of 2019 the rift has further developed, but the iceberg to be (A) has not detached. By mid-August of 2019 the rift has nearly led to detachment of an iceberg (A), the snowline is at 1075 m. In June of 2020 the iceberg has detached and there is a considerable melange of ice between the iceberg (A) and the main terminus. By Sept. 11, 2020 the iceberg remains in much the same position.

The glacier has retreated 2.4 km since 2018, and now terminates at yellow arrow 1 km downglacier of the junction of the two main tributaries. The iceberg has maintained an area of ~1 km². The snowline in 2020 is at 1125 m indicating another of mass balance loss for the glacier. The lake is now 7 km long and the lake area is ~7.5 km²up from 5 km²in 2016. The retreat of this glacier paralells that of its neighbor Excelsior Glacier that retreated 4.7 km from 1994-2018. This continues to be a developing lake district including Grewingk Glacier.

Ellsworth Glacier in Landsat images from 2016-2020. Red arrow is the 2016 terminus location, yellow arrow is the 2020 termins location, pink arrow is the rift, purple dots is the snowline, iceberg is Point A.

Ellsworth Glacier in 2019. Point A is future iceberg is, yellow arrow is 2020 terminus locations and pink arrow is rift. Image from Johnstone Adventure Lodge.

Yalik Glacier, Alaska Retreat and Lake Expansion 1986-2019

On March 23, 2020April 24, 2024 By mspeltoIn alaska glacier retreat1 Comment

Yalik Glacier (Y) in 1986 and 2019 Landsat images. Red arrow is the 1986 terminus location and yellow arrow the 2019 terminus location. Petrof Glacier (P) is the western neighbor.

Yalik Glacier drains an icefield on the Kenai Peninsula, glaciers draining east are in the Kenai Fjords National Park, which has a monitoring program. From 1950-2005 all 27 glaciers in the Kenai Icefield region examined retreated (Giffen et al 2014). Yalik Glacier retreated 1057 m from 1950-1986, a rate of-29 m/year and 797 m from 1986-2000, a rate of 57 m/year (Giffen et al 2014). Here we update the retreat using Landsat images from 1986, 2000, 2018 and 2019.

In the 1950 USGS map of the region Yalik Glacier terminates on a braided outwash plain, and does not have a proglacial lake. By 1986 there is a 300-400 m wide fringing proglacial lake particularly on the eastern margin with an area of 0.6 km². The glacier has retreated from the outwash plain into the developing proglacial lake basin. By 2000 the proglacial lake has expanded to 1.3 km² due to the ~800 m retreat. In 2018 the proglacial lake has expanded to 2.1 km² and a second proglacial lake has formed on the eastern margin. This proglacial lake will merge with the main lake as the terminus retreats from a peninsula extending from the eastern margin. A bedrock knob has emerged east of Point 1 indicating substantial glacier thinning since 2000. In 2019 the total proglacial lake area is 2.4 km². The glacier has retreated 1500 m since 1986 and 700 m since 2000, the latter period has a retreat rate of 34 m/year. The former braided river that exited the glacier is now a single meandering stream channel as it leaves the proglacial lake. The retreat of Yalik Glacier is more than nearby Grewingk Glacier and less than nearby Excelsior Glacier.

What is driving the retreat is continued warming including warm summers. The glacier generated few icebergs during this retreat, indicating melting not calving is the key factor. The 2019 Alaska Climate Review indicates 2019 was the state’s warmest year, see Anchorage example from this report below. Temperatures in nearby Homer averaged 4.2 F above normal with June-August averaging 4.4 F above normal. These conditions also led to forest fires in the area reducing the 2019 image clarity due to forest fire smoke from the Swan Lake fire that burned ~167K acres.

Yalik Glacier in 2000 and 2018 Landsat images. Red arrow is the 1986 terminus location and yellow arrow the 2019 terminus location. Point 1 is west of a bedrock knob that has emerged due to glacier thinning.

USGS map of Yalik Glacier in 1951

From the 2019 Alaska Climate Review .

Retreat of Grewingk Glacier, Alaska 1986-2014

Grewingk Glacier drains west toward the Kachemak Bay, Alaska terminating in a proglacial lake in Kachemak Bay State Park. The glacier drains an icefield on the Kenai Peninsula, glaciers draining west are in the Kenai Fjords National Park. The glaciers that drain east toward are in the Kenai Fjords National Park, which has a monitoring program. Giffen et al (2008) observed the retreat of glaciers in the region. From 1950-2005 all 27 glaciers in the Kenai Icefield region examined are retreating. Giffen et al (2008)observed that Grewingk Glacier retreated 2.5 km from 1950-2005. Here we examine Landsat imagery from 1986-2014 to illustrate the retreat of the glacier. The icefront continues to calve into the expanding pro-glacial lake.

1951 based USGS Topographic map Seldovia C-3

The red arrow is the 1986 terminus location at the midpoint, the yellow arrow is the 2014 mid-point terminus location. In 1951 the glacier extended beyond the peninsula at the red arrow into the wider portion of the lake. By 1986 the glacier had retreated into the narrow section of the lake extending east into the mountains, the southern margin of the terminus is further advanced than the northern margin. The orange dots indicate discoloration of the glacier surface from volcanic ash deposited on the glacier surface from Augustine Volcano in 1986. In 1989 there is not a marked change. In a 1996 Google Earth image, there is considerable icebergs indicating a recent collapse of a section of the terminus. The pink arrow indicates concentric crevasses, indicating a depression, the red line is the terminus in 1996 and the brown line the 2003 terminus.

By 2001 the terminus has retreated m, and the glacier front is now oriented north-south across the lake. In 2003 the depression from 1996 now has a small supraglacial lake, the terminus has retreated 500 m on the southern margin and 200 m on the northern margin. In 2013 the glacier has retreated an additional 600 m and the southern margin has now receded further upvalley than the northern margin. Blue arrows indicate direction of glacier flow. By 2014 the glacier has retreated 1.4 km since 1986, 50 m per year. There is an increase in the glacier slope 2.5 km above the terminus where crevassing increases. This suggests the lake will end by or at this point, which would then lead to a reduction in retreat rate.

This retreat follows that of Pederson Glacier, Four-Peaked Glacier and Spotted Glacier. The continued reduction in glacier size leads to changes to the Kachemak Bay estuary. Kachemak Bay is the largest estuarine reserve in the National Estuarine Research Reserve System. It is one of the most productive, diverse estuaries in Alaska, with an abundance of Steller sea lions, seals, sea otters, five species of Pacific salmon, halibut,herring, dungeness crabs and king crabs (NERRS, 2009). The estuary salmon fishing industry is, one of Kachemak Bay’s most important resources and livelihoods.

1986 Landsat Image