Glacial Lake Outburst Floods in Alaska and the Himalayas Show Evolving Hazards in a Warming World

Subject :Geography

SECTION: Physical Geography

Context:

A small glacial lake outburst flood (GLOF) occurred in Alaska at Mendenhall Glacier, similar to GLOF event at Chungthang, Sikkim due to bursting of South Lhonak lake.

Glacier Lake Outburst Flood (GLOF):

Glacier-dammed lakes 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 (GLOF).

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.
Glacier-dammed lakes, like Suicide Basin off of Mendenhall Glacier, are instead dammed by the glacier itself.
These glacial lakes tend to repeatedly fill and drain due to a cyclic opening and closing of a drainage path under the ice. The fill-and-drain cycles can create hazards.

How glacier lake hazards are changing in Alaska

The glacier-dammed lakes in Alaska have decreased in volume since 1985 but the frequency of outbursts remains unchanged.
Warming air temperatures are causing glaciers to melt and thin, lowering the tub walls and therefore accommodating less water. That reduces the total volume of water available for a potential glacial lake outburst flood.
Smaller lakes have had less significant change in area over time.
GLOF in Alaska: Suicide Basin, near Juneau; Skilak Glacier-Dammed Lake, which affects the Kenai River; and Snow Lake, which impacts the Snow River.

How will rising temperatures affect these lakes?

Glacier loss in Alaska is accelerating as temperatures rise, that may result in formation of more glacial lakes thus more potential hazards.

Source: The Wire