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Every summer, residents near the Mendenhall River in Juneau, Alaska, watch water levels with great care. When the river swells quickly, it often signals that a nearby lake called Suicide Basin has broken its ice dam. This event triggers a powerful glacial lake outburst flood. For nearly fifteen years, these floods in Alaska's capital have grown larger and more destructive. These events release a sudden rush of icy water that can cause immense damage.
To stop this threat, the U.S. Army Corps of Engineers is planning a major new project. The plan involves building a permanent channel to drain the lake before water levels rise too high. This engineering solution aims to prevent future outbursts completely. Early cost estimates suggest the project could cost between $613 million and one billion dollars. However, Suicide Basin is not just a local issue. It is a sign of a global environmental crisis. As the Earth warms, glacial lakes are growing fast everywhere, especially in mountain ranges like the Himalayas and the Andes. This change is rapidly altering the physical landscape of Alaska.
A recent study analyzed 140 of Alaska's largest glacial lakes from 2018 to 2024. The results were clear: these lakes are now growing at more than twice the speed seen between 1986 and 1999. To predict future growth, researchers used satellite pictures and estimates of glacier thickness. This process helped them map the shape of the land hidden under the ice. The analysis shows that as glaciers keep melting, these lakes could eventually grow to be more than four times their current size. Such a huge expansion would make outburst floods much more dangerous for ecosystems, transportation routes, and people downstream.
Glacial lakes are common spots found at the edges of melting glaciers. They often look like bright blue-green pools with floating icebergs. Years of satellite observations show that the number of these lakes and their total water volume are increasing fast. This trend is a direct result of glaciers moving backward due to rising global temperatures. These lakes are held back by unstable natural dams made of glacier ice or piles of rocky debris called moraines. Because these dams are often weak, the lakes they hold can be extremely dangerous.
Between 1985 and 2020, lakes in Alaska held back by glacier ice broke through their barriers more than 1,150 times. Since Alaska has few people, most of these outbursts did not damage many buildings. However, there are critical exceptions, such as Suicide Basin and Snow Lake on the Kenai Peninsula, where more people live near the danger zones. When an outburst happens, a huge volume of icy water rushes down river valleys. This sudden flood can change the environment with immense power. The floodwaters erode riverbanks, drop new dirt and rocks, rip up trees, and destroy habitats for fish.
The problem is getting worse globally. Another study found that outburst floods from lakes held by moraine dams are happening more often. In the steep, narrow valleys of the Himalayas, these events have caused devastating results. They have destroyed hydropower stations and roads, washed away entire villages, and caused hundreds of deaths over the years. Globally, more than 15 million people live in areas at risk from glacial lake outburst floods. Scientists are working to predict where new lakes will form to help communities prepare.
Glacial lakes can form in a few different places: on top of a glacier, in valleys next to it, or directly at its toe. The study found that the fastest-growing lakes are located at the glacier's toe. Many of these lakes sit inside deep basins carved out by the glacier's heavy weight over thousands of years. Researchers mapped these hidden basins, which are technically called glacial-bed overdeepenings. They did this by using satellite data to measure ice height and then subtracting estimates of ice thickness. The remaining shape reveals the depression in the bedrock under the glacier.
The findings were clear. More than 80% of the observed lake expansion happened inside these mapped basins. This shows that finding these overdeepened areas is a reliable way to predict where lakes are most likely to form. Using this method, the research team calculated that existing glacial lakes in the region could eventually expand to four times their current area. This growth could cover an extra 1,640 square miles, or 4,250 square kilometers. One lake alone at the end of the massive Malaspina Glacier could grow by an extra 570 square miles. This expansion would make it the second-largest lake in the entire state.
As glaciers keep retreating, they will expose thousands of these basins. Many will eventually fill with meltwater. In total, Alaska has over 5,500 square miles of overdeepened land. This points to a landscape that will look very different in the coming decades. The presence of a lake can also speed up a glacier's retreat. When a glacier ends in a lake, the relatively warmer water melts the ice much faster than air would. This causes the glacier to flow more quickly and pull back further. The study confirmed this cycle, finding that glaciers ending in lakes are shrinking 23% to 56% faster than glaciers that end on dry land.
Scientific models mixing future climate predictions with glacier physics paint a serious picture of what lies ahead. By the year 2100, glaciers are expected to lose between 26% and 41% of their total volume. This represents the potential disappearance of 49% to 83% of all glaciers worldwide. This large-scale ice loss is worrying for many reasons. First, melting glaciers are currently the single largest cause of rising sea levels. Second, glaciers act as natural water towers. Their meltwater feeds major rivers, particularly in Asia. Changes in the timing and volume of this meltwater could affect water supplies for millions of people. Finally, the retreat of glaciers creates new dangers, including outburst floods. The landscapes we know are visibly changing. With these changes come increased risks that communities around the world must learn to manage effectively.