Warming world triggers Glacial floods in Alaska and Himalayas

In August 2023, the Mendenhall River in Juneau, Alaska, experienced a historic rise in water levels within hours. This surge wasn’t due to heavy rainfall, but rather a small glacier-formed lake situated next to the Mendenhall Glacier.

Glacier-dammed lakes are common in Alaska. They form when a side valley loses its ice faster than the main valley, creating an ice-free valley that fills with water. These lakes can remain stable for years until they reach a breaking point where the immense water pressure opens a section beneath the glacier.

This sudden and catastrophic release of water from a glacier-fed lake is known as a glacial flood or GLOF. These floods can cause significant damage as they move downstream over hours or days.

Glacier Lake Bursts threaten millions globally

Glacier-fed lake bursts have caused destruction worldwide, destroying homes, infrastructure, and even claiming lives. They have resulted in hundreds of fatalities in Europe and thousands in South America and Central Asia. Approximately 1.5 million people globally live downstream of these lakes, with those residing in Asia’s high mountains being most at risk.

A glacier-fed lake flood in the Himalayas on October 5, 2023, resulted in numerous fatalities in India as it swept away bridges, damaged a hydroelectric power station, and flooded small towns. Satellite imagery revealed a significant drop in the lake level within hours.

Researchers are currently studying the threats posed by Alaska’s glacier-formed lakes, especially those created by glacier breakage. They are examining how these lakes are changing as global temperatures rise.

When glaciers block lakes, some glacier-formed lakes are dammed by moraines - piles of rock and debris left behind as the glacier retreats. Excessive pressure build-up in the lake due to heavy rainfall, avalanches or landslides can breach these dams, leading to devastating floods. People believe that Lonak Lake in the Himalayas flooded Indian cities in October 2023 when it occurred.

Glacier-dammed lakes like Mendenhall Glacier’s Suicide Basin are dammed by the glacier itself. These glacial lakes undergo repeated cycles of filling and draining due to the periodic opening and closing of drainage channels beneath the ice. This cycle can pose a threat if it occurs every two years or even several times a year.

Alaskan Glacier lakes dry up repeatedly

A recent study published in Nature Communications revealed that researchers have identified 120 glacier-formed lakes in Alaska, with 106 of them having dried up at least once since 1985. These lakes have collectively dried up 1,150 times in the past 35 years, averaging 33 incidents per year where a lake spills its contents downstream, potentially creating hazardous conditions.

Remote areas host many of these lakes and often remain unnoticed, while communities locate others nearby. For instance, Suicide Basin is within five miles of the state capital and has frequently dried up over the past decade.

The study found that the volume of lakes formed by glacier rupture in Alaska has decreased since 1985, while the frequency of eruptions has remained constant. This suggests a regional decline in threats from glacier melt lakes due to less stored water being available, a trend observed for glacier melt lakes globally.

As temperatures rise, glacier loss in Alaska is accelerating rapidly. Given Alaska’s abundance of glaciers and ice-filled valleys, there’s a high likelihood that melting valleys will lead to new lake formation, creating new hazards.

People believe that many of these lakes formed in remote locations and satellite images showing changes over time are the only way to detect them. Given the increasing number of glacier-formed lakes and their potential threat to human life, there is a severe lack of early warning and monitoring systems.

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