Retreating glaciers and expanding meltwater lakes in Alaska

Today’s Image of the Day from NASA Earth Observatory features a satellite view of retreating glaciers in Alaska, where meltwater is rapidly expanding glacial lakes. The image was captured on August 4, 2024 by the Landsat 8 satellite.

“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,” said NASA.

Retreating glaciers in Alaska

“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,” noted NASA. 

The retreat of the glaciers, as well as the growth of the lakes, are visible in the image. When compared to an image captured by Landsat 5 in the summer of 1984, the changes are even more evident.

NASA elaborated on the extent of the glacier retreat from 1984 to 2024. “During this period, Yakutat Glacier’s main arm retreated 4.3 miles, while Alsek Glacier’s northern and southern arms retreated 3.3 miles and 3.4 miles, respectively. Grand Plateau Glacier’s northern arm lost the most, retreating 4.8 miles.”

Glacial lakes doubled in size 

“Collectively, the three lakes more than doubled in size over 40 years. In 1984, they covered about 50 square miles. By 2024, they spanned 90 square miles. 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,” said NASA.

Pelto noted that the lakes 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.

“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,” said NASA.

Understanding glacier retreat 

Glacier retreat is a significant phenomenon driven primarily by global warming the results from rising greenhouse gas emissions. 

As temperatures rise, glaciers lose more ice during the summer melt than they can regain in winter snowfall, causing them to shrink over time. This process has profound implications for ecosystems, water resources, and global sea levels.

Glacial lakes

When glaciers retreat, they often leave behind depressions in the landscape that can fill with meltwater, forming glacial lakes. These lakes are typically bounded by natural dams made of rock, ice, or moraine – accumulations of debris left behind by the glacier’s movement. 

Over the past century, the number and size of glacial lakes worldwide have increased significantly due to the accelerating pace of glacier retreat. This trend is especially evident in high-altitude regions like the Himalayas, the Andes, and the Alps, as well as in polar areas such as Alaska and Greenland.

Positive and negative impacts 

Glacial lakes can have both positive and negative impacts. They provide critical water sources for downstream communities, support biodiversity, and sometimes offer opportunities for hydropower development or tourism. 

However, they also pose serious risks. The dams holding back these lakes can fail suddenly, causing glacial lake outburst floods (GLOFs). These catastrophic events can devastate downstream areas, destroying infrastructure, agricultural lands, and habitats while endangering human lives.

Monitoring changes

Understanding glacier retreat and glacial lake formation requires a multidisciplinary approach, combining climate science, hydrology, and geology. 

Monitoring these changes is essential to mitigate associated risks and adapt to the evolving landscape shaped by a warming planet.

Glacier retreat worldwide

Studies and satellite observations show that most glaciers in almost all regions of the world are shrinking. 

Melting glaciers contribute significantly to global sea level rise, which threatens coastal communities and ecosystems.

The retreat of glaciers is considered one of the clearest indicators of climate change. Some glaciers are retreating at unprecedented rates, indicating accelerating climate impacts.

Image Credit: NASA Earth Observatory

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