Alaskan glacier bigger than Switzerland may lead to largest US threat

A detailed "body scan" of Malaspina Glacier- one of Alaska's most iconic glaciers- revealed that its bulk lies below sea level and is undercut by channels, making it likely to retreat faster than previously thought, according to a new study published in JGR Earth Surface.  

The findings underscore the fragility of an extensive glacial system that could cause the largest ice loss from an Alaskan glacier within this century. At that point, it would also contribute a measurable volume to global sea level rise. 

Malaspina: the iconic Alaskan glacier

Lead author Brandon Tober, a UArizona Department of Geosciences doctoral student, and colleagues used the Arizona Radio Echo Sounder, or ARES. Previously, this instrument was used for a NASA-funded mission that recorded annual variations in the thickness of glaciers, sea ice, and ice sheets in Greenland, Alaska, and Antarctica from between 2009 and 2021.

The plane's ice-penetrating radar "X-rayed" the glacier as it traversed it from the air, creating a complete "3D body scan" of the glacier and underlying bedrock.

The data indicated that the Malaspina glacier is mostly below sea level and has multiple channels cutting through its bed that go at least 21 miles from where the glacier meets the shore up towards its source in the Saint Elias Mountains.

"We can speculate that the channels, the big troughs beneath the glacier, are routing meltwater that comes out at the coast," Tober said in a press release. 

The researchers concluded that Malaspina has the capacity to deliver 560 cubic kilometers, or 134 cubic miles, of ice to the ocean, assuming that the ice will experience large-scale shedding. In other words, Malaspina alone has the potential to raise the sea level by 1.4 millimeters, or just about 1/16 inch.

"This might not sound like much, but to put this in perspective, all Alaskan glaciers combined contribute about 0.2 millimeters per year to global sea level rise – a rate that tops all other glaciated regions on Earth apart from the Greenland and Antarctic ice sheets," Tober explained. 

'Largest landscape transformation within the U.S'

And that's not all. The Malaspina Glacier is situated in Wrangell Saint Elias National Park and Preserve- the largest national park in the U. S. At 13.2 million acres, it's bigger than Yellowstone National Park, Yosemite National Park, and the entire country of Switzerland put together.

"The potential loss of Malaspina and opening of a new bay along Alaska's coastline may be the largest landscape transformation within the U.S. that we could witness during this century," Tober said, "and it may lead to the loss of up to 500 square miles of park land."

The full study was published in JGR Earth Surface and can be found here.

Study abstract:

Malaspina Glacier, located on the coast of southern Alaska, is the world's largest piedmont glacier. A narrow ice-cored foreland zone undergoing rapid thermokarst erosion separates the glacier from the relatively warm waters of the Gulf of Alaska. Glacier-wide thinning rates for Malaspina are greater than 1 m/yr, and previous geophysical investigations indicated that bed elevation exceeds 300 m below sea level in some places. These observations together give rise to the question of glacial stability. To address this question, glacier evolution models are dependent upon detailed observations of Malaspina's subglacial topography. Here, we map 2,000 line-km of the glacier's bed using airborne radar sounding data collected by NASA's Operation IceBridge. When compared to gridded radar measurements, we find that glaciological models overestimate Malaspina's volume by more than 30%. While we report a mean bed elevation 100 m greater than previous models, we find that Malaspina inhabits a broad basin largely grounded below sea level. Several subglacial channels dissect the glacier's bed: the most prominent of these channels extends at least 35 km up-glacier from the terminus toward the throat of Seward Glacier. Provided continued foreland erosion, an ice-ocean connection may promote rapid retreat along these overdeepened subglacial channels, with a global sea-level rise potential of 1.4 mm.