The phrase “moving at a glacial pace” denotes plodding progress. But there are circumstances where glaciers move at the speed of massive landslides. Glacial landslides, or glacial detachments, are a phenomenon of a warming planet. They happen quickly like a landslide or avalanche, and they also pose a threat to areas downslope from the glacier.
Glacial landslides occurred in 2013 and 2015 in the St. Elias Mountains, Alaska. Both events involved the Flat Creek Glacier. Between the two events, the volume of material released was 24 to 31 million cubic meters of ice and rock. When these glacial detachments occurred, the outflow traveled more than 11 kilometers (7 miles) downslope and into the valleys and canyons below.
The Flat Creek Glacier detachments also have similarities to documented detachments in the Aru mountains of Tibet.
Detachment mechanisms
A common causal factor in the Alaskan and Tibetan glacial landslides was meltwater. These slides occurred during summer months at the height of the melt season. But meltwater wasn’t the only factor.
The Flat Creek detachment was the result of two processes. So, the thin tongue of the glacier, near its downslope edge, froze solid to the underlying rock. This frozen tongue then prevented the normal forward creep that allows the glacier to move downslope gradually. Pressure from the ice accumulating at higher elevations created a 70-meter bulge above the tongue.
But in addition to the increasing stress at the tongue, another factor was at work. The frozen tongue blocked normal meltwater drainage. Meltwater from glaciers tends to move through cracks and crevices to the base of the ice mass. Then, once it reaches the base, it flows downslope at the interface between the glacier and the underlying rock. Water is an excellent lubricant; therefore, too much water at the ice-rock contact destabilizes the glacier.
The combination of increasing upslope stress and pooling meltwater behind the tongue eventually took its toll. When the tongue finally gave way, the rest of the glacier started sliding on the water-lubricated basal contact. The result was a catastrophic failure and a massive glacial landslide.
Implications
Global warming brings with it previously unknown side effects, and glacial landslides are one such side effect. Large glacial detachments like the ones in Alaska and Tibet have been reported in other areas of the world also. So far, the destructive flows from these detachments have only impacted wilderness areas. But developing a greater understanding of glacial detachment processes is potentially crucial for assessing risk in developed areas that are immediately downslope from existing glaciers.
Is there a risk to the Seattle urban communities nestled in valleys at the base of Mt. Rainier? Some of these communities are already at risk from lahar flows related to volcanic activity on the mountain. Glacial landslides could be another worry.
ArcheanWeb:
Washington: home to dangerous volcanoes (Source: ArcheanWeb) – https://archeanweb.com/2019/12/12/washington-home-to-dangerous-volcano/ Also:
The world’s water towers (Source: ArcheanWeb) – https://archeanweb.com/2019/12/19/the-worlds-water-towers/ Also:
Sources
Glacier detachments: A new hazard in a warming world? (Source: Science News) – https://www.sciencedaily.com/releases/2020/04/200428131709.htm Also:
Kristy Tiampo, John Sykes, Jasmine S.S. Hansen, Etienne Berthier, Ethan Welty, Matthias Leopold, Michael Loso, Mylène Jacquemart. What drives large-scale glacier detachments? Insights from Flat Creek glacier, St. Elias Mountains, Alaska. Geology, 2020; – https://pubs.geoscienceworld.org/gsa/geology/article-abstract/doi/10.1130/G47211.1/583706/What-drives-large-scale-glacier-detachments?redirectedFrom=fulltext Also:
Feature Image: Tongue of the Gran Paradiso glacier (Modified) – By Marie-Lan Taÿ Pamart – Own work, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=85778838
