Glaciers alongside the coastal plain of southeastern Alaska are quickly retreating, spilling meltwater into increasing proglacial lakes. One such lake—fed by the receding Alsek Glacier—has grown a lot that it reworked a small mountain into a brand new island.
The Alsek Glacier as soon as enveloped this rocky mound—often known as Prow Knob—close to its terminus. Over the previous 40 years, each of the glacier’s arms have retreated greater than 3 miles (5 kilometers), creating Alsek Lake. Landsat photos captured in 1984 and 2025 doc this transformation, exhibiting that the glacier lastly misplaced contact with Prow Knob this summer season, in accordance with a statement from NASA Earth Observatory. Now, the 2-square-mile (5-square-kilometer) landmass is totally surrounded by the waters of Alsek Lake.
In accordance with Mauri Pelto, a glaciologist at Nichols Faculty, this development is more likely to proceed. Certainly, rising world temperatures have accelerated the speed of glacial retreat all over the world. Now that the Alsek Glacier has misplaced contact with Prow Knob, its ice is much less steady and extra susceptible to calving, which might additional speed up its retreat.
Alsek Glacier’s surprising resilience
Glaciologists have been monitoring the Alsek Glacier and its proglacial lake for many years. Photographer and self-educated glaciologist Austin Post (1922-2012) imaged the glacier’s terminus in 1960 and later advised Pelto that he named the rocky mound for its resemblance to a ship’s prow, in accordance with the NASA assertion.
Based mostly on the speed of the Alsek Glacier’s retreat between 1960 and 1990, Publish and Pelto beforehand predicted it could disconnect from Prow Knob in 2020. Surprisingly, the glacier held on 5 years longer than anticipated, at the same time as world temperatures have continued to rise.
NASA’s satellite tv for pc observations point out that the Alsek Glacier formally separated from Prow Knob someday between July 13 and August 6, finishing the mound’s transformation into an island. This occasion affords scientists a uncommon likelihood to match long-term predictions with real-world glacier conduct.
Utilizing eyes within the sky to trace glacial soften
NASA’s Landsat satellites have been significantly helpful for monitoring glacial retreat because the first launched in 1972. These two photos had been captured by the Thematic Mapper instrument on Landsat 5 and the Operational Land Imager-2 instrument on Landsat 9. Evaluating them reveals how icemelt has reshaped the area over the many years.
Since 1984, Alsek Lake has grown from roughly 17 sq. miles (45 sq. kilometers) to about 29 sq. miles (75 sq. kilometers) right this moment. Although it’s primarily fed by meltwater from Alsek Glacier, it’s additionally fed and impounded by a quickly thinning tongue of the Grand Plateau Glacier, in accordance with the National Park Service.
Glacial retreat is a significant driver of worldwide sea degree rise, however the modifications at Alsek Glacier present the way it can even reshape total landscapes. This could have ecological and sociocultural penalties, in accordance with NPS. By way of satellite tv for pc observations and different types of monitoring, scientists will proceed to trace the Alsek Glacier’s retreat to know how this ever-changing area fares in a warming local weather.
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