In parts of Alaska, water is replacing ice. As glaciers thin and retreat, meltwater collects at their fronts, forming proglacial lakes. According to an analysis by Mauri Pelto, a glaciologist at Nichols College, three such lakes in the southeastern part of the state have grown rapidly in recent decades.
A trio of glaciers—Yakutat, Alsek, and Grand Plateau—descend from inland mountains and flow onto the coastal plain southeast of Yakutat borough, ending at Harlequin Lake, Alsek Lake, and Grand Plateau Lake. The retreat of the glaciers and growth of the lakes is evident in this image pair, acquired with the Landsat 5 and Landsat 8 satellites in the summers of 1984 (left) and 2024 (right).
During this period, Yakutat Glacier’s main arm retreated 7.0 kilometers (4.3 miles), while Alsek Glacier’s northern and southern arms retreated 5.3 kilometers (3.3 miles) and 5.5 kilometers (3.4 miles), respectively. Grand Plateau Glacier’s northern arm lost the most, retreating 7.8 kilometers (4.8 miles).
Lakes now fill the void left by the retreating glaciers. Collectively, the three lakes more than doubled in size over 40 years. In 1984, they covered about 50 square miles (130 square kilometers). By 2024, they spanned 90 square miles (240 square kilometers). That’s an area larger than Seneca Lake (67 square miles)—one of the Finger Lakes in New York, which also have a glacial origin.
“The lakes that are forming in this region are immense, starting at the mountains and spreading toward the coast, making this a new lake district that is unique in our nation,” Pelto said.
Millions of other lakes, named and unnamed, dot the state. But this system has grown fast, so much so that Pelto thinks it might represent the fastest lake growth in the United States this century.
The lakes are also changing in other ways. Alsek Lake appears much bluer in the 2024 image, indicating that the lake is receiving less fine-grained sediment, or “glacial flour,” from meltwater streams. As the lake receives less sediment, it will turn darker blue, Pelto said, allowing more light to penetrate the water and aid aquatic life and fishery development.
NASA Earth Observatory image by Wanmei Liang, using Landsat data from the U.S. Geological Survey. Story by Kathryn Hansen.
