The Suicide Basin Problem
Every summer, residents near the Mendenhall River in Juneau, Alaska, watch the water. When the river level begins rising unusually fast, they know what is happening: Suicide Basin, a small glacially-dammed lake about five miles upstream, has breached. Water that accumulated over weeks behind a glacier dam is now rushing downstream in what glaciologists call a glacial lake outburst flood — a GLOF. The events are unpredictable, powerful, and as Alaska's glaciers retreat under warming temperatures, they are becoming more frequent.
Suicide Basin has become a case study in the growing hazard of glacially-dammed lakes, but it is far from the only one. New research examining satellite imagery across Alaska's glaciated regions finds that the area covered by glacial lakes has increased substantially over the past two decades, tracking closely with glacier mass loss. As ice retreats, it leaves behind terrain that is increasingly likely to trap meltwater — and release it catastrophically.
How Outburst Floods Work
Glacially-dammed lakes form when a glacier acts as a natural dam, trapping meltwater in adjacent or subglacial basins. The ice dam can fail in several ways: warm water can melt through the base of the glacier in a process called subglacial drainage; the lake water level can rise to the point where it floats the glacier off its bed; or structural weakening can allow sudden drainage.
When the dam fails, stored water can be released extremely rapidly — volumes that took weeks to accumulate can drain in hours, producing flood waves far larger than drainage basin rivers can accommodate. The resulting floods carry sediment, boulders, and debris with enormous destructive force. In populated valleys, they damage bridges, roads, and buildings; destroy fish habitat; and threaten lives.
The Research Findings
The new study, using multi-decade satellite records combined with ground-truth measurements from instrumented sites, documents both the expansion of glacial lake area and changes in outburst flood characteristics. Among the key findings: the total area of proglacial and ice-marginal lakes in Alaska has grown substantially, with the largest increases concentrated where glacier retreat has been most rapid.
Importantly, the study finds that lake size alone is insufficient to predict which lakes will drain suddenly. A small lake at a structurally weak ice margin can produce a dangerous flood; a large lake with a more stable dam configuration may drain gradually. This makes hazard assessment particularly challenging and strengthens the case for real-time monitoring infrastructure: lake level sensors, GPS monitoring of glacier movement, and early warning systems that can give downstream communities enough lead time to evacuate.
This article is based on reporting by Phys.org. Read the original article.
