Gilkey Glacier Retreat Leads to Rapid Lake Expansion in 2019

On September 17, 2019April 24, 2024 By mspeltoIn alaska glacier retreat

Gilkey Glacier in 1984 and 2019 Landsat images indicating retreat of 4300m, tributary separation and 5 km² lake expansion. A=Terminus tongue, B=Battle Glacier, G=Gilkey Glacier and T=Thiel Glacier.

Gilkey Glacier draining the west side of the Juneau Icefield has experienced dramatic changes since I first worked on the glacier in 1981. The Gilkey Glacier is fed by the famous Vaughan Lewis Icefall at the top of which Juneau Icefield Research Program (JIRP) has its Camp 18 and has monitored this area for 70 years. Here we examine the changes using Landsat images from 1984, 2014, 2018 and 2019. Landsat images are a key resource in the examination of the climate change response of these glaciers (Pelto, 2011). The August 17th 1984 image is the oldest high quality Landsat image, I was on the Llewellyn Glacier with JIRP on the east side of the icefield the day this image was taken. JIRP was directed by Maynard Miller at that time and by Seth Campbell now.

In 1984 Gilkey Glacier terminated in a new proglacial lake that had and area of 1.5 km² (#1). At #2 Thiel and Battle Glacier merged and then joined Gilkey Glacier. Arrow #3 and #4 indicates valleys which tongues of the Gilkey Glacier flow into, at #3 the glacier extended 1.6 km upvalley. At arrow #4 the glacier extended 1.5 km up Avalanche Canyon. At #6, #7 and #9 tributaries flow into the Gilkey Glacier. At #8 Antler Glacier is a distributary glacier terminus that spilled into a valley terminating short of Antler Lake.

By 2014 the proglacial lake had expanded to 3.65 km² as the glacier has retreated 3200 m. Thiel and Battle Glacier have separated from Gilkey Glacier and from each with a retreat of 2600 m for Thiel Glacier and 1400 m for Battle Glacier. The glacier no longer flows into the valley at #4. Tributaries at #6 and #9 no longer reach Gilkey Glacier. At #7 there is not a direct flow connection, but is still an avalanche connection. At #8 Antler Glacier has retreated 2200 m.

In 2018 and 2019 the snowline on the Juneau Icefield has been the highest of any year since observations began in 1984. This will accelerate mass loss and lead to continued extensive retreat. In 2018 the snowline was at 1600-1650 m on Sept. 16. In 2019 the snowline on Gilkey Glacier was 1650-1700 m on Sept. 10. In July of 2019 the terminus tongue of the glacier reached across the junction of the Gilkey and Battle Valley, separating the two proglacial lakes. By September 10, the glacier tongue had broken off leading to the two lakes joining expanding the size of the proglacial lake to 6.5 km². The terminus has retreated 4300 m since 1984, while the lake has increased in size by more than 400%. The retreat will continue leading to additional lake expansion just as is occurring at Meade and Field Glacier.

The expansion of Gilkey Lake into the Battle Valley in 2019 Landsat images.

Gilkey Glacier in 1984 and 2019 Landsat images indicating retreat of 4300m, tributary separation and 5 km² lake expansion. A=Terminus tongue, B=Battle, Bu=Bucher, G=Gilkey, T=Thiel, V=Vaughan Lewis. Snowline=purple dots.

Gilkey Glacier in 2014 and 2018 Landsat images indicating retreat, snowline elevation and lake expansion.

Widespread Retreat Gilkey Glacier System, Alaska

Gilkey Glacier drains the west side of the Juneau Icefield and has experienced widespread significant changes since I first worked on the glacier in 1981. Here we examine the changes from the August 17, 1984 Landsat 5 image to the August 21, 2014 image from newly launched Landsat 8. Landsat 5 was launched in 1984, Landsat 8 launched in 2013. The Landsat images have become a key resource in the examination of the mass balance of these glaciers (Pelto, 2011). The August 17th 1984 image is the oldest Landsat image that I consider of top quality. I was on the Llewellyn Glacier with the Juneau Icefield Research Program (JIRP) on the east side of the icefield the day this image was taken. JIRP was directed by Maynard Miller at that time and by Jeff Kavanauagh now. The Gilkey Glacier is fed by the famous Vaughan Lewis Icefall at the top of which JIRP has its Camp 18 and has monitored this area for 60 years. Here I examine changes both in images and text below. The same analysis in a more depth is contained in the screen capture video of the same images. Choose the format you prefer and let me know which works for you.

There are seven locations noted in the 1984 and 2014 image that are the focus of more discussion in a set of three more focused images

1984 Landsat Image

2014 Landsat image

Arrow #1 indicates the Gilkey Glacier terminus area. Gilkey Glacier had begun to retreat into a proglacial lake by 1984, the lake was still just 1 km long. A short distance above the terminus the Gilkey was joined by the sizable tributaries of the Thiel and Battle Glacier. By 2014 the main glacier terminus has retreated 3200 m, the lake is now 4 km long. A lake that did not exist in USGS maps from 1948. Thiel and Battle Glacier have separated from the Gilkey Glacier and from each other. Thiel Glacier retreated 2600 m from its junction with Gilkey Glacier from 1984-2014 and Battle Glacier 1400 m from its junction with Thiel Glacier and 3500 m from the Gilkey Glacier. Melkonian et al (2013) note the fastest thinning in the Gilkey Glacier system from to is near the terminus and in the lower several kilometers of Thiel Glacier.

Above: 1984-2014 Comparison of Gilkey Glacier terminus area with Landsat imagery

Arrow #3 and #4 indicates valleys which tongues of the Gilkey Glacier flow into. In 1984 at #3 the glacier extended 1.6 km upvalley ending where the valley split. The portion of the Gilkey flowing into the valley had a medial moraine in its center. At arrow #4 the glacier extended 1.5 km up Avalanche Canyon. In 2014 at #3 the glacier tongue ends 1.2 km from the valley split, and the medial moraine does not enter the valley. At #4 the glacier has retreated 1.3 km, leaving this valley nearly devoid of a glacier.

Above: Comparison of the Avalanche Canyon area 1984-2014.

Further upglacier arrow #5 indicates a side glacier that in 1984 featured an unending system of glacier flowing down the steep mountain sides into the valley bottom. By 2014 two rock ribs extend along most of the east and west valley walls separating the glaciers on mountain side from the main valley glacier, which has as a result been reduced in width and velocity. At arrow #6 a tributary glacier is seen merging with Gilkey Glacier in 1984. By 2014 this tributary no longer reaches the Gilkey Glacier, ending 300 m up the valley wall. At arrow #7 the Little Vaughan Lewis Icefall in 1984 is seen merging with the Gilkey Glacier across a 300 m wide front. This I can attest from seeing the glacier that summer to be an accurate observation. By 2014 at arrow #7 the Little Vaughan Lewis Icefall no longer feeds ice directly to the Gilkey Glacier. There is still avalanching but not a direct flow connection. JIRP has Camp 19 in this area, a spectacular area of ongoing research by JIRP. The main Vaughan Glacier Icefall is still impressive, just south of the rib beyond arrow #7. Measurements of snowpack are made annually by JIRP above the icefall, and indicate a mean snow depth exceeding 3 m in early August, note image below of measuring annual snow layers in a crevasse at head of the icefall. Pelto et al (2013) summarize the results of this ongoing research that Chris McNeil (USGS) is working to enhance with newer technology. The terminus change of all Juneau Icefield glaciers from 1984-2013 has been summarized in a previous post. The 2015 season will be of interest, since the area had a remarkably warm yet wet winter. This will lead to high ablation at lower elevations, likely a higher snowline than usual, but above the Vaughan Lewis Icefall will those warm wet events dumped snow? The 2014 winters season was warm and the snowline seen in the 2014 satellite imagery was at 1500 m, yet snowpack at 1760 m on the Vaughan Lewis Glacier was 3.3 m deep in late July. This has been the case in the past with warm wet winters featuring heavy snow above 1600 meters on the icefield. JIRP will be in the field answering this question in 2015.

Above: Comparison 1984-2014 of the Vaughan Lewis Glacier area

Crevasse stratigraphy Vaughan Lewis Glacier.

Gilkey Glacier Ogive Spacing and Retreat

On May 29, 2011April 1, 2014 By mspeltoIn alaska glacier retreat, Glacier Observations3 Comments

The Gilkey Glacier is a 32 km long outlet glacier flowing west from the Juneau Icefield. From 1948 to 1967 the Gilkey Glacier retreated 600 m and in 1961 a proglacial began to form. By 2005 Gilkey Glacier has retreated 3900 m from the 1948 terminus location. The glacier is currently terminating in this still growing lake, notice the new bergs and rifting at the glacier terminus. The retreat has been resulted from and in a thinning of in the lower reach of the glacier and the separation from Battle and Thiel Glacier. A major tributary to Gilkey Glacier, is Vaughan Lewis Glacier. At the base of the Vaughan Lewis Icefall where the Vaughan Lewis Glacier joins the larger Gilkey Glacier ogives form, as seen from above and below the icefall (Scott McGee). The ogives form annually and provide a means to assess annual velocity in this section of the glacier. Aerial photography of the ogives from the 1950’s combined with current satellite image provide the opportunity to assess ogive wavelength over a 50 year period, providing a long term velocity record for Gilkey Glacier. An ogive is a bulge-wave that forms annually due to a seasonal acceleration of the glacier through an icefall. The acceleration is enhanced in icefalls that are horizontally restricted. In most cases we do not have specific measurements of velocity through all season to ascertain the timing of the accelerated period, though typically spring would be the fastest. After formation the bulges move down glacier and a new bulge is formed the following year. The resulting train of ogives extending down glacier can be used to estimate the ice velocity by measuring the peak to peak separation between adjacent waves. Ogives can be visually identified as a series of arcuate wave crests and troughs pointing down glacier. Downglacier from this formation point the crests and troughs gradually flatten until the ogives are merely arcuate light and dark bands on the surface of the glacier. The dark bands are dense, blue and dusty ice that is compressed during summer, whereas the light bands are bubbly, white, air-filled ice that is compressed during winter.
In 1981 one of my tasks was to ski out through the top of the icefall inserting stakes in the crazily crevassed region to track summer velocity for the Juneau Icefield Research Program (JIRP). This has been completed often but not most years by JIRP. What we discovered was that velocity in 1981 had not changed from the 1960’s and 1970’s. Today we have frequent satellite imagery of the ogives to ascertain annual velocity that can be compared to the few aerial photographic records, in this case from 1056 and 1977. In several recent years Scott McGee of JIRP has specifically surveyed the distance between the first 11 ogive crest below the icefield. A comparison of the the ogives in 1956, 1977 and 2005 is possible by overlaying the images below. . The distance from the first to the 40th ogive has gone from 6.8 km in 1956 to 6.75 km in 1977 to 6.2 km in 2005. In 1956 and 1977 the first ten ogives spanned 1500 meters indicating an annual glacier velocity of 150 meters. From 2003-2007 the distance of the first ten ogives averaged 1440 m, or 144 meters per year. The change in velocity is quite small, compared to the large retreat of the glacier. One other key measure of the ogive surveying program is the surface elevation. A longitudinal profile containing 179 survey points was established at the base of the Icefall in 2001-2007. This profile begins in the trough immediately upglacier of the crest of the first wave ogive and continues downglacier nearly 1.8 kilometers to a point where the amplitude of the ogives becomes zero (Graphs and data from JIRP) During this six year time period, the surface has lowered an average of 17 meters – nearly 3 meters per year – along the longitudinal survey profile, with a maximum of 22 meters. This substantial thinning at the base of the icefall indicates reduced discharge through the icefall from the accumulation zone above. This will lead to further retreat and velocity reduction of Gilkey Glacier.