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.

Excelsior Glacier, Alaska Retreat Leads to Lake Doubling in Size

On April 29, 2019April 25, 2024 By mspeltoIn alaska glacier retreat3 Comments

Excelsior Glacier retreat from 1994 to 2018 in Landsat images from 1994, 2011 and 2018. The red arrow is the 1994 terminus location and the yellow arrow is the 2018 terminus location. Point A and B are on the south and northwest side of the eastern tributary of the glacier.

Excelsior Glacier is an outlet glacier of the Sargent Icefield, on the Kenai Peninsula of Alaska, that has terminated in an expanding Big Johnstone Lake since 1941. Here we examine the retreat of Excelsior Glacier from 1994-2018 using Landsat imagery. In 1909 the glacier ended on the strip of forested land between the lake and the ocean (Molnia, 2007). By 1950 the glacier had retreated 2 km from this strip of land creating the new lake (USGS-Molnia, 2008). This blog post is source of an article published by the Washington Post and from NASA Earth Observatory.

In 1994 the glacier was 21 km long and had retreated 5.5 km from the southern margin of Big Johnstone Lake, this is a rate of ~100 m/year since the lake began forming 1941. There is a glacier dammed lake just south of Point A named Excelsior Lake. By 2001 the glacier had retreated 800 m from the 1994 position, a rate of ~100 meters per year, and the glacier dammed lake south Point A remains, along with a few large icebergs. By 2011, the glacier had retreated beyond the former glacier dammed lake and ended at the prominent ridge just north of this former lake, adjacent to Point A, and the new inlet that replaces it. The glacier has retreated 2200-2500 m depending where on the front the measurement is made. By 2013 the glacier has retreated back to the junction of the two main tributaries between Point A and B. The snowline is at 900 m, with more than 80% of the glacier falling below the snowline. A calving Alaskan glacier typically needs at least 60% of its area above the snowline consistently to be in equilibrium. In 2011 and 2013 images there are large icebergs in Big Johnstone Lake indicating active calving. In 2018 the snowline is at 925 m again leaving an insufficient accumulation zone to support the glacier. Big Johnstone Lake has expanded to a length of 10.2 km, with an area of 18 km². The glacier has retreated 4.7 km from 1994-2018, a rate of ~200 m/year, twice the previous rate. The eastern and western tributaries have now fully separated. Johnstone Adventure Lodge visited the eastern tributary, they call it Roan Glacier, glacier in May of 2019, the photograph they provided below indicates the glacier has receded from the lake. The glacier in 2018 is 15 km long having lost ~30% of its length in 24 years. Big Johnstone Lake is nearing its maximum size as the glacier surface slope steepens within 1 km of the current terminus, indicating a substantial increase in elevation of the base of the glacier. The lake width has changed little and is 1.4-1.8 km wide in the region the terminus has been retreating through during the last 25 years are has doubled from 9 to 18 km². There will be a reduction in calving and retreat rate as the lake development nears completion, in 2018 for the first time there are no visible icebergs. Johnstone Adventure Lodge observed 15-20 harbor seals during their first visit to the glacier front in 2019, 10 of them had pulled out on icebergs. A reduction in icebergs will make the lake less attractive to harbor seals.

Excelsior Glacier follows the pattern of retreat of the neighboring Ellsworth Glacier and Pedersen Glacier of the Harding Icefield. This glacier is seen as a model for the impending retreat of Brady Glacier (Pelto et al, 2013).

Excelsior Glacier retreat from 1994 to 2018 in 1984 USGS map and Landsat images from 2001 and 2013. The red arrow is the 1994 terminus location and the yellow arrow is the 2018 terminus location. Point A and B are on the south and northwest side of the eastern tributary of the glacier.

“Roan Glacier” the eastern tributary of Excelsior Glacier in May 2019 now terminating on an outwash plain. Image from Johnstone Adventure Lodge.

Excelsior Glacier Retreat, Alaska

On June 6, 2013June 6, 2013 By mspeltoIn Glacier Observations3 Comments

Excelsior Glacier in Alaska has terminated in a lake for the last century. Here we examine the retreat of this glacier from 1984 to 2011 using Landsat imagery. This glacier is seen as a model for the impending retreat of Brady Glacier examined in a paper we just published (Pelto et al, 2013). In 1909 the glacier ended on the strip of forested land between the lake and the ocean (Molnia, 2007). By 1950 the glacier had retreated 2 km from this strip of land creating the new lake (USGS-Molnia, 2008) In 1909 the glacier had ended on land at the south end of the lake, indicating a retreat of 4.5-5.0 km in approximately a 75 year period. In 1984 (first image below) Excelsior Glacier ended at the pink arrow and the lake extending beyond the terminus was 4.7 km long, the yellow arrow indicates the 2011 position and just south (under) the arrow is a glacier dammed lake. The lake width has changed little and is 1.4-1.8 km wide in the region the terminus has been retreating through during the last 30 years. By 1989 the glacier had retreated 500 m and the lake was filled with numerous icebergs. By 2001 the glacier had retreated 1500-1700 m from the 1984 position, a rate of 100 meters per year, and the glacier dammed lake south of the yellow arrow is still apparent, as are a couple of large icebergs. The 2003 Google Earth image indicates further retreat and again a couple of large icebergs and a large crack near the center of the terminus indicating a new iceberg getting ready to separate. By 2011 the glacier had retreated past the formerly glacier dammed lake and ended at the prominent ridge just north of this former lake and the new inlet that replaces it. The glacier has retreated 3400-3700 m depending where on the front the measurement is made. This is a rate of over 100 meters per year since 1984.
Another big change is the thinning and narrowing of the tributary entering on the east side of the glacier north of the terminus. This is illustrated in the last image with a combined 1989 image left and 2011 rigth and the red arrows pointing out three significant points of thinning and new rock-moraine exposure. This glacier has behaved in a similar fashion to so many Alaskan glacier from the nearby Bear Glacier, to British Columbia’s Melbern Glacieror Porcupine Glacier and southeast Alaska’s Chickamin and Norris Glaciers of southeast Alaska