Tag: Landsat images glacier retreat

Glacier Retreat on Yakutat Foreland, Alaska Generates Fastest Lake Growth in United States

On By mspeltoIn alaska glacier retreat, glacier climate change, Glacier Observations2 Comments
Yakutat, Alsek and Grand Plateau Glacier retreat from 1984 to 2024 has led to the three lakes expanding from 130 km2 to 240 km2 as illustrated by this pair of Landsat images. Fastest lake expansion in the nation in this period.

Three adjacent glaciers terminating on the coastal plain near Yakutat, Alaska have had a spectacular retreat in the last 40 years leading to rapid lake growth; Yakutat Glacier, Alsek Glacier and Grand Plateau Glacier. This is the story of the most rapid area of lake growth in the United States this century.

Alsek Glacier descends from the Fairweather Range terminating in Alsek Lake on the coastal plain. In the early part of the 20th century the glacier terminated at Gateway Knob (G) near the outlet of Alsek River from Alsek Lake, with just a small fringing lake present (Molnia, 2005). At that time it had a joint terminus with Grand Plateau Glacier. In 1960 the glacier had a single terminus downstream of an unnamed island in Alsek Lake, that Austin Post (USGS Glaciologisst) told me reminded him of a boats prow. This “Prow Knob” (P) much like Gateway Knob a century ago stabilized the terminus (Pelto, 2017).  The glacier retreated 5-6 km by 1984 from Gateway Knob with the lake growing to an area of 45 km2. From 1984-2024 the retreat has been: 5.3 km for the northern terminus,  5.5 km for the southern terminus and 7.8 km for the northern arm of Grand Plateau Glacier. Alsek Lake has grown from 45 km2 to 75 km2 since 1984. In Octobrer 2024 there remains a narrow connection to Prow Knob that will not survive another year.

Alsek Glacier retreat from 1999-2013 in Landsat images. Red arrows mark the 1984 terminus location, yellow arrows the 2022 terminus location, AR=Alsek River, GP=Grand Plateau, PK=Prow Knob, G=Gateway Knob, A=glacier junction, B=tributary separation, C=tributary separation, D=tributary confluence.

Alsek Glacier retreat from 2018-2021 in Landsat images. Red arrows mark the 1984 terminus location, yellow arrows the 2022 terminus location, pink arrows indicate tributary separation, AR=Alsek River, GP=Grand Plateau, PK=Prow Knob, G=Gateway Knob, A=glacier junction, B=tributary separation, C=tributary separation, D=tributary confluence.

Yakutat Glacier, Alaska experienced a spectacular retreat losing 45 km² from 2010-2018, as a result of rising ELA leading to rapid thinning of the lower glacier (Truessel et al, 2013).  The Yakutat Glacier during the 1894-1895 Alaskan Boundary Survey ended near a terminal moraine on a flat coastal outwash plain. By 1906 the glacier had retreated from the moraine and a new lake was forming, Harlequin Lake.  By 1984 the lake had expanded to an area of 50 km2. The 2018 image compares the 2010 position (yellow dots) with 2018 (orange dots), indicating an area of 45 km² lost in less than a decade (NASA EO, 2018). There are some small icebergs in 2018.  By 2024 further retreat has expanded the total lake area to 105 km2.  The main terminus retreated 7 km. The ability to produce icebergs as large as in 2015 has been lost as the calving front has been restricted by the Peninsula which is now 3 km long, leaving less than a 3 km wide calving front.   The narrower calving front and reduced water depth should in the short term reduce retreat. Truessel et al (2015) modelling indicated a reduced rate of retreat from 2020-2030, which supports the expected reduced calving.  Their model also indicates the glacier will disappear between 2070 and 2110 depending on the warming scenario.  

Expansion of Harlequin Lake due to retreat of Yakutat Glacier indicated on these 2010 and 2018 Landsat images. Yellow dots mark the ice front, orange dots the 2010 margin in 2018.
Expansion of Harlequin Lake due to retreat of Yakutat Glacier, yellow boundary marks the deglaciated region on these Landsat images from 1999 and 2020.

Grand Plateau Glacier drains southwest from Mount Fairweather in southeast Alaska. The glacier advanced during the Little Ice age to the Alaskan coastline. Early maps from 1908 show no lake at the terminus of the glacier. The 1948 map (below) shows three small distinct lakes at the terminus of the main glacier and a just developing lake at the terminus of the southern distributary terminus (D). The distance from the Nunatak (N) to the terminus was 11 km in 1948. The lake at D is 400 m wide.In 2024 the lake area has grown further to 49 km2, as a result of a retreat of 8 km since 1948 and 5.5 km since 1984. Today a second island is emerging at the terminus, Point A. The distributary tongue to the southeast now terminates in a lake that is now 5.2 km long, a 4.8 km retreat since 1948 and 2.6 km since 1984. The combination of higher snowlines and increased calving into the terminus lake will continue to lead to retreat of this still mighty river of ice (Pelto, 2024).

There will be continued glacier retreat and lake expansion in 2025, as the new lake district continues to expand as a result of climate change.  Loso et al (2021) note that retreat of Grand Plateau Glacier will change the outlet of Alsek Lake from Dry Bay to the Grand Plateau Lake, creating one larger lake. 

Grand Plateau Glacier retreat from 1984 to 2013 in Landsat images. Main tributaries indicated by red arrows also showing snowline. Orange arrows indicate 1984 terminus and pink arrows 2013 terminus.

Bas d’Arolla Glacier, Switzerland No Longer Reaches Valley

On By mspeltoIn switzerland glacier retreat

Bas d’Arolla Glacier in Landsat images from 1990, 2001 and 2017.  Red arrow is 1985 terminus, yellow arrow 2017 terminus location, purple dots annual snowline. A=Bas d’Arolla O=Otemma

Bas D’Arolla Glacier is one of the glaciers where the terminus is monitored annually by the Swiss Glacier Monitoring Network (SCNAT). Here we examine changes in this glacier from 1985 to 2017 including changes in the terminus, snowline elevation and tributary connection during this period using Landsat Imagery. SCNAT reports that the glacier advanced 136 m from 1972-1987, retreated at a rate of 17.6 m/year from 1987-2001, and  23 m/year from 2001-2017.  The main accumulation zone between Pigne d’Arolla and Mont Collon extends from 2900 m to 3400 m, with a saddle to Otemma Glacier at 3000 m. An icefall extends from 2400 m to 2900 m. In 1985 the glacier had a low elevation terminus tongue extending from the base of an icefall at 2400 m to just below 2200 m (see map below).

In 1985 the glacier terminates at the red arrow at an elevation of 2160 m and the snowline is at 2940 m.  In 1990 the terminus had advanced slightly up to 1987 and then retreated slightly with not significant overall change and the snowline is again at 2940 m.  By 2001 the glacier has retreated 220 m, and the snowline is at 2900 m.  In 2015 the snowline is at 3100 m with the saddle to Otemma Glacier not in the accumulation zone.  This saddle should always be snow-covered.  In 2017 the snowline is at 3200 m, the saddle with Otemma Glacier is again exposed and is in fact glacier ice, indicating that snow and firn has been lost and this is no longer part of the persistent accumulation zone.  The main terminus tongue in 1985 that occupied the valley floor and extended 500 m from 2400 m to the terminus is gone, with a total retreat of 600 m since 1985.  The glacier retreat is similar to that of neighboring Otemma Glacier and more substantial than Gietro Glacier, and reflects an annual snowline that is too high to maintain the glacier terminus tongue.  the Bas d’Arolla valley floor is now glacier free. The river discharges into the Rhone River Basin, which has substantial hydropower south of Lac Geneva.  Schaefli et al (2018) observe that of the 50% of Swiss power that comes from hydro, glacier mass loss alone has provided 3-4% of the total, not a sustainable model.  Bliss et al (2014) indicate that the Swiss Alps have passed peak glacier runoff.

Bas d’Arolla Glacier in Landsat images from 1985 and 2017.  Red arrow is 1985 terminus, yellow arrow 2017 terminus location, purple dots annual snowline. A=Bas d’Arolla O=Otemma

Map of the Bas d’Arolla Glacier and Mont Collon area, from Swisstopo

Google Earth image indicating flow, and the fact that the glacier now terminates in the icefall region, no longer reaching the valley floor.

Alsek Glacier, Alaska Retreat & Glacier Separation

On By mspeltoIn alaska glacier retreat

Alsek Glacier in a 1984 Landsat image and 2017 Sentinel image.  Red arrows indicate 1984 terminus, yellow arrows 2017 terminus location, pink arrows tributaries that joined the glacier in 1984 and purple dots the snowline.  AR=Alsek River, G=Gateway Knob and P=Prow Knob.

Alsek Glacier descends from the Fairweather Range terminating in Alsek Lake on the coastal plain. The glacier terminated at Gateway Knob (G) near the outlet of Alsek River from Alsek Lake in the early part of the 20th century (Molnia, 2005). At that time it had a joint terminus with Grand Plateau Glacier. The glacier retreated 5-6 km by 1984 along the central margin from Gateway Knob. The glacier remained connected with the Grand Plateau Glacier in 1984. In 1960 the glacier had a single terminus joining downstream of an unnamed island in Alsek Lake, that Austin Post told me reminded him of a boats prow. This “Prow Knob” (P) much like Gateway Knob a century ago stabilizes the terminus. Retreat from this knob will lead to an increase in retreat of Alsek Glacier. Here we examine the change from 1984-2017 with Landsat and Sentinel imagery.

In 1984 the terminus location is denoted with red arrows it has separated into two termini on either side of “Prow Knob”. The northern terminus tongue is located on a narrow island on the north side of Alsek Lake. The southern tongue merges with the northern arm of Grand Plateau Glacier. Two tributaries at the pink arrows merge with the main glacier. In 1984 the snowline is at 900 m. By 1999 the northern tongue has retreated from the narrow island, which exposes the terminus to enhanced calving. The southern terminus has separated from the Grand Plateau Glacier. In 1999 the snowline is at 900 m. By 2013 the northern terminus has retreated almost to the northern end of “Prow Knob” and the southern terminus is directly south of “Prow Knob” in a 1.8 km wide channel. By 2016 two tributaries of Alsek Glacier are fully detached from the glacier, pink arrows. In 2017 the northern terminus tongue has retreated 3.7 km since 1984 into the 2.0 km wide channel on the northeast side of “Prow Knob”. The center of the southern terminus has retreated 3.0 km since 1984 and remains in the channel on the south side of “Prow Knob”. The length of the calving front has declined from an 8 km long calving front in 1984 to a 4 km calving front in 2017. In both 2016 and 2017 the snowline is at 1200 m, at this elevation the mass balance of the glacier will be significantly negative driving further retreat. Larsen et al (2007) indicate thinning in the lower Alsek Glacier of 3+m/year in the last half of the 20th century, indicating the glacier is a in a long term adjustment to climate change.  The retreat of this glacier is similar to that of Walker Glacier and North Alsek Glacier, and less than that of the northern arm Grand Plateau Glacier to which it was connected in 1984 or Yakutat Glacier a short distance north.   

Alsek Glacier in a 1999 Landsat image .  Red arrows indicate 1984 terminus, yellow arrows 2017 terminus location, pink arrows tributaries that joined the glacier in 1984 and purple dots the snowline.   P=Prow Knob.

Alsek Glacier in 2014 Google Earth Image,indicating flow directions. 

Alsek Glacier in a 2016 Landsat image .  Red arrows indicate 1984 terminus, yellow arrows 2017 terminus location, pink arrows tributaries that joined the glacier in 1984 and purple dots the snowline.   P=Prow Knob.