Glacial lake outburst floods in Alaska and the Himalayas show evolving hazards in a warming world

By Brianna Rick, University of Alaska Anchorage

In August 2023, residents of Juneau, Alaska, watched as the Mendenhall River swelled to historic levels in a matter of hours. The rushing water undercut the riverbank and swallowed whole stands of trees and multiple buildings.

The source for the flood was not heavy rainfall – it was a small glacial lake located in a side valley next to the Mendenhall Glacier.

Glacier-dammed lakes like this are abundant in Alaska. They form when a side valley loses its ice faster than the main valley, leaving an ice-free basin that can fill with water. These lakes may remain stable for years, but often they reach a tipping point, when high water pressure opens a channel underneath the glacier.

The rapid and catastrophic drainage of lake water that follows is called a glacial lake outburst flood, or GLOF for short. The flood waters race downstream over hours or days and often hit unexpectedly.

https://youtu.be/opoTgIj97SU?si=DAoKmDI5kkL1Q3hf

Glacial lake outburst floods have destroyed homes, infrastructure and human life around the world. They have killed hundreds of people in Europe and thousands of people in both South America and central Asia. Globally, an estimated 15 million people live downstream from these lakes, with those in Asia’s high mountains at greatest risk.

Flooding from a glacial lake in the Himalayas on Oct. 5, 2023, left dozens of people dead in India as water swept away bridges, damaged a hydropower station and flooded small towns. Satellite images showed that the lake level dropped markedly within hours.

I study Alaska’s glacial lakes and the hazards that glacier-dammed lakes in particular can create. Our latest research shows how these lakes are changing as global temperatures rise.

When glaciers hold back lakes

Some glacial lakes are dammed by moraines – mounds of rock and debris that are left behind as a glacier retreats. Too much pressure from extreme rainfall or an avalanche or landslide into the lake can burst these dams, triggering a devastating flood.

Read Full Story https://theconversation.com/glacial-lake-outburst-floods-in-alaska-and-the-himalayas-show-evolving-hazards-in-a-warming-world-214829