Every summer, people living near the Mendenhall River in Juneau, Alaska, keep a close eye on the water level. When the river level begins to rise rapidly, it’s a sign that Suicide Basin, a small glacier-dammed lake 5 miles up the mountains, has broken through the glacier again and a glacial lake outburst flood is underway.
After nearly 15 straight years of ever-larger and more damaging floods in Alaska’s capital city, the U.S. Army Corps of Engineers is discussing an ambitious and expensive solution: create a permanent drain from the lake that would prevent it from reaching outburst stage.
The initial cost estimates for the project range from US$613 million to $1 billion.
Suicide Basin is just one example of a growing problem from glacial lakes that threaten communities around the world, particularly in the Himalayas and Andes, and is transforming Alaska’s landscape as global temperatures rise.
In a new study, colleagues and I documented the evolution of 140 of the largest glacial lakes in Alaska between 2018 and 2024. We found they are expanding about 120% faster on average today than they were from 1986 to 1999 – more than twice as fast.
Using ice thickness data to reconstruct the shape of the land beneath these glaciers, we found that these glacial lakes could become more than four times larger than they are today as the glaciers melt, increasing the potential for damage to downstream ecosystems and infrastructure from glacial lake outburst floods.
The Hazards of Glacial Lakes
Glacial lakes, often the color of aquamarine gems and sparkling with icebergs, are common around the margins of glaciers around the world. Years of satellite images have documented a dramatic increase in their number, area and volume – a direct response to glaciers retreating as global temperatures rise.
Tenuously held back by moraines – the jumble of rock and sediment deposited by glaciers at their edges – or dammed by glacier ice, these lakes are anything but stable.
Between 1985 and 2020, ice-dammed lakes in Alaska alone broke through their barriers and drained more than 1,150 times. Alaska’s vast landscape and low population density means that the impact of these drainages on human infrastructure was fairly minimal, with a few notable exceptions, including Suicide Basin and Snow Lake, on the Kenai Peninsula.
However, the enormous amount of icy water rushing down rivers with each outburst can transform ecosystems, altering river channels through erosion and sediment deposition, tearing out trees and other vegetation, and damaging fish habitat.
A recent study found that glacial lake outburst floods from moraine-dammed lakes are occurring at an accelerating rate. In the steep, narrow valleys of the Himalayan Mountains, the impact of these events are acute: destroyed hydropower stations, roads and entire villages wiped away, taking hundreds of lives over the years.
More than 15 million people globally live in areas at risk of glacial lake outburst floods. Mapping where these lakes might form and expand can help people living downstream prepare. That’s what we did in Alaska.