Is Harlequin Lake, Alaska the fastest Growing Glacier Lake in North America this Century?

On January 6, 2021April 23, 2024 By mspeltoIn alaska glacier retreat

Yakutat Glacier, Alaska in 1999 and 2020 Landsat image illustrating expansion of Harlequin Lake by 40.5 km². Yellow line is the 1999 margin, orange line is the 2020 margin, and yellow dots indicate the margin of the lake shoreline. Point A indicates the 1987 terminus location, Point X and Y the 1999 terminus location. Main terminus now extends south near Point C. Northern terminus extends west from Point B.

Yakutat Glacier, Alaska has experienced a spectacular retreat in the last decade losing 45 km² from 2010-2018 (Pelto, 2018). During the 1894-1895 Alaskan Boundary Survey Yakutat Glacier ended on a flat coastal outwash plain. A decade later the glacier had retreated from the plain and a new lake was forming, Harlequin Lake. From 1906-1987 the glacier retreated ~10.5 km. From 2000-2010 the terminus area thinned ~10 m/year, the glacier retreated ~1200 m losing 5.8 km² of area (Trussel et al 2013). Here we examine Landsat imagery to quantify the retreat from 1999-2020 to identify Harlequin Lake expansion during this century.

In 1999 the glacier has a single terminus extending 4.1 km across the lake from Point Y to Point X. Point B is under the glacier near the junction of the tributaries, while Point C is in the midst of the glacier. A ~1.4 km retreat up to 2010 with faster retreat on the north side and an expansion of the lake along the southern margin led to a 5.7 km long main calving front, and a 4 km long southern margin. An aerial image of the glacier in 2010 indicates significant rifting, blue arrows, that pre-conditioned the glacier for a substantial 2013 breakup. The rifts extend through the width of the glacier and typically form when thinning has led to a glacier region reaching approximate flotation (Benn, Warren and Mottram, 2007). In 2013 the glacier has separated into two separate calving fronts. The calving front extending west from Point B is 3 km wide, and the calving front extending south from Point B is 6.5 km long. There is a large area of icebergs and ice melange in front of the terminus, yellow dots in image below, resulting from the collapse. In 2015 the snowline is quite high at 2200 m, leaving very little of the glacier in the accumulation zone. In 2015 a large iceberg detached pink arrow, that is ~3.7 km², indicating continued rapid calving retreat. From 2013 to 2018 the glacier retreated from Point B to Point C on the northern side a distance of 4.6 km in five years 920 m/year. By 2018 the Peninsula extending across the lake from Point C is 2.5 km long. The terminus is resting on this and adjacent shoals across 50% of its width. The northern terminus extending west from Point B has changed little from 2013-2018. The 2018 image compares the 2010 position (yellow dots) with 2018 (orange dots) indicating an area of 45 km² lost in eight years, though not all of it is lake (Pelto, 2018; NASA 2018). The comparison of 1999 to 2020 illustrates the area of lake expansion between the 1999 (yellow) terminus position, 2020 terminus position (orange) and yellow dots along the lake shoreline. The lake area growth is 40.5 km² since 1999 with an overall area loss of ~56 km².

Landsat images from 2010 and 2018 with terminus indicated by yellow dots in both, the orange dots indicate 2010 margin on 2018 image, and pink arrows indicate icebergs.

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 of the main terminus. The northern terminus is at a narrow point, as it recedes further the embayment widens and the retreat should increase.

The glacier thinned at a rate of ~4 m/year from 2000-2010 indicating how far out of equilibrium the glacier has been (Trussel et al 2013). The Yakutat Glacier does not have a high accumulation zone and the recent increase in the snowline elevation and thinning of the glacier have led to a substantial shrinking of the accumulation zone and thinning of the glacier in the accumulation (Truessel et al 2013). This glacier does not have a persistent significant accumulation zone in 2015, 2016 and 2018 and 2019 cannot survive (Pelto, 2010; NASA 2018).

2010 image of the Yakutat Glacier terminus reach with blue arrows indicating rifts.

Yakutat Glacier in 2013 Landsat image.

Yakutat Glacier in 2015 Landsat image.

Yakutat Glacier Terminus Collapse Nears Completion, 45 km2 lost 2010-2018

On September 14, 2018April 27, 2024 By mspeltoIn alaska glacier retreat

Landsat images from 2010 and 2018 with terminus indicated by yellow dots in both, the orange dots indicate 2010 margin on 2018 image. Point A indicates the 1987 terminus location, pink arrows indicate icebergs. Main terminus now extends south near Point C. Northern terminus extends west from Point B.

Yakutat Glacier, Alaska has experienced a spectacular retreat in the last decade losing 45 km² from 2010-2018. 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. From 1906-1948 the glacier retreated an additional 5 km. From 1948-1958 the glacier retreated 3.6 km. Here we examine Landsat imagery to quantify the retreat from 2010-2018. This is an update to a Yakutat Glacier 2016 post

In 2010 the glacier has just retreated from the peninsula at Point A, the valley at D was deglaciated, a small strip of bedrock-sediment was exposed at C from that had been beneath the glacier, and B was still well inland of the terminus. An aerial image of the glacier indicates significant rifting, blue arrows, in 2010 that leads to the substantial 2013 breakup. Rifts are not just crevasses, as they typically extend to the base of the glacier along part of the glacier. They typically form in areas of a glacier that are near flotation. In this case an area that has thinned until approximate flotation (Benn, Warren ann Mottram, 2007). In 2013 there is a large area of icebergs and melange in front of the terminus, yellow dots. By 2013 the northern arm of the glacier had retreated 6.4 km from the peninsula at A toward the peninsula at B. The central arm of the glacier toward C had retreated 7.5 km and the retreat on the southern edge of the glacier was 6.5 km. In 2015 the snowline is quite high at 2200 m, leaving very little of the glacier in the accumulation zone. In 2015 a large iceberg detached pink arrow, that is 5 km by ~1 km. In 2016 the snowline is again around 2200 m. From 2013 to 2016 the glacier retreated from Point B to Point C on the northern side and to Point E on the southern side this is a distance of 10.2 km in thirty years since 1987 or 340 m/year. In 2016 the Peninsula extending across the lake from Point C is 2.5 km long. The terminus is resting on this and adjacent shoals across 50% of its width. The iceberg has diminished to 2.5 km long and 700 m wide, pink arrow. The northern terminus extending west from Point B has changed little from 2013-2016. The 2018 image compares the 2010 position (yellow dots) with 2018 (orange dots), indicating an area of 45 km² lost. The main terminus retreated 7 km. There are some small icebergs in 2018. 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. The northern terminus near Point B has experienced limited retreat since 2013.

The glacier has thinned by more 200 m on average according to the preliminary thickness change maps from a U. Alaska-Fairbanks project (Truessel et al 2013) and updated by Truessel et al (2015). The Yakutat Glacier does not have a high accumulation zone and the recent increase in the snowline elevation and thinning of the glacier have led to a substantial shrinking of the accumulation zone and thinning of the glacier in the accumulation (Truessel et al 2013). This glacier does not have a persistent significant accumulation zone in 2015, 2016 and 2018 and cannot survive (Pelto, 2010). Truessel et al (2015) modelling indicates 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. For a calving glacier to be in equilibrium it needs to have more than 60 % of its area snowcovered at the end of the summer, this was not achieved in 2015, 2016 or 2018.. The glacier is in the midst of a large ongoing retreat. The retreat rate and calving mechanism is similar to that of Grand Plateau Glacier, Alsek Glacier and Gilkey Glacier. However, unlike these Yakutat Glacier lacks an accumulation zone, a better analog is East Novatak Glacier, which also has a lower elevation accumulation zone.

2010 image of the Yakutat Glacier terminus reach with blue arrows indicating rifts.

Landsat images from 2013 with terminus indicated by yellow dots. Point A indicates the 1987 terminus location. Note large area of melange and icebergs.

Landsat images from 2015 with terminus indicated by yellow dots. Point A indicates the 1987 terminus location. Main terminus now extends south near Point C. Northern terminus extends west from Point B. Note large iceberg that calved in 2015, pink arrow.

Landsat images from 2016 with terminus indicated by yellow dots. Point A indicates the 1987 terminus location. Main terminus now extends south near Point C. Northern terminus extends west from Point B.Note large iceberg that calved in 2015, pink arrow.

Yakutat Glacier Terminus Collapse, 10 km retreat 1987-2016

On April 21, 2017May 1, 2024 By mspeltoIn alaska glacier retreat

Landsat images from 1987 and 2016 with terminus indicated by yellow dots. Point A indicates the 1987 terminus location and Point E the 2016 terminus location.

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. Surveys of the terminus of the glacier indicated a retreat of 1 kilometer in that decade. From 1906-1948 the glacier retreated an additional 5 km. From 1948-1958 the glacier retreated 3.6 km. The retreat is evident in comparing the Yakutat B-3 quadrangle, from 1958 photography, and Landsat imagery from 1987, 2010, 2013 and 2016. Points A-E are the same in each image and the yellow dots are the terminus. In 1987 the terminus was just retreating from a peninsula marked A, the valley at D was filled with ice, there was no break in the surface at C and B was well inland of the terminus. By 2010 the glacier had retreated from A, the valley at D was deglaciated, a small strip of bedrock-sediment was exposed at C from what had been beneath the glacier, and B was still well inland of the terminus. By 2013 the northern arm of the glacier had retreated 6.4 km from the peninsula at A toward the peninsula at B. The central arm of the glacier toward C had retreated 7.5 km and the retreat on the southern edge of the glacier was 6.5 km. The glacier had retreated on average more than 6.6 km in 27 years, a rate of 240 m/year. From 2013 to 2016 the glacier had retreated from Point B to Point C on the northern side and to Point E on the southern side this is a distance of 10.2 km in thirty years 340 m/year.

Recently the glacier has been the focus of a study by the University of Alaska, Faribanks they have set up a time lapse camera to record frontal changes. The goal is to understand the controls on calving into Harlequin Lake of this glacier. More amazing than the retreat has been the observed thinning of the glacier. The glacier has thinned by more 200 m on average according to the preliminary thickness change maps from the UAF project (Truessel et al 2013) and updated by Truessel et al (2015). The Yakutat Glacier does not have a high accumulation zone and the recent increase in the snowline elevation and thinning of the glacier have led to a substantial shrinking of the accumulation zone and thinning of the glacier in the accumulation (Truessel et al 2013). This glacier does not have a persistent significant accumulation zone and cannot survive (Pelto, 2010), Truessel et al (2015). modelling suggests the glacier will disappear between 2070 and 2110 depending on the warming scenario. For a calving glacier to be in equilibrium it needs to have at least 60 % of its area snowcovered at the end of the summer. The glacier is in the midst of a large ongoing retreat. The retreat rate and calving mechanism is similar to that of Grand Plateau Glacier, Bear Lake Glacier and Gilkey Glacier. However, unlike these Yakutat Glacier lacks an accumulation zone, a better analog is East Novatak Glacier, which also has a lower elevation accumulation zone.

Yakutat terminus map