A detailed “body scan” of the Malaspin Glacier, one of Alaska’s most iconic glaciers, has revealed that its bulk lies below sea level and is undermined by channels that could allow ocean water to gain access if its coastal barrier erodes. This makes the glacier more vulnerable to seawater intrusion than previously thought and could cause it to retreat faster than predicted.
Findings published by researchers at the University of Arizona Journal of Geophysical Researchhighlight the fragility of a very large ice system that could result in the loss of a significant amount of National Park Service ice and land and contribute a measurable amount to global sea-level rise.
“The loss of this glacier is likely to be the largest loss of ice from an Alaskan glacier this century,” said study lead author Brandon Tober, a doctoral student in the Arizona Department of Earth Sciences.
The area in front of Malaspina Glacier, an area of permafrost with pure ice below the surface, is “falling apart” in the face of rising global temperatures, Tober said. Permafrost refers to ground that remains frozen for two or more years.
“As this coastal barrier erodes and gives way to large lagoons, primarily through the collapse of ice cliffs, ocean water may eventually gain access to the glacier,” Tober said. “Once it gets to the front of the glacier, it can melt the ice even faster and start the glacier retreating.”
Forming a vast ice sheet located right on the shore of southeast Alaska, Malaspina is the world’s largest foothill glacier, a type of glacier that flows from steep mountains onto a wide plain, essentially forming an “ice pancake” that spills out onto a wide coastal plain from the St. Elias Mountains. A thin land barrier separates the glacier from the relatively warm waters of the Gulf of Alaska. Historical satellite images show that these bodies of water have been expanding over time over the past few decades, forming a lagoon system just in front of the glacier.
Traditionally, researchers rely on mathematical models to estimate glacier thickness, Tober said, but they vary widely in their ability to accurately predict glacier thickness. These models often rely on measurements of how fast the glacier is moving across the surface to predict the glacier’s depth, similar to how the speed of a river’s current is used to obtain information about its depth and channel shape.
“We know that Alaskan glaciers are melting and thinning rapidly in many places, but we don’t know exactly how thick they are, so we can’t accurately predict future mass loss,” Tober said. “If we do not know the thickness and topography of the layer, we cannot accurately model their future evolution.”
To get a better idea of Malaspina’s future, the researchers needed to obtain a detailed “body scan” of its shape and thickness. To do this, Tober’s research team used the Arizona Radio Sounder, or ARES, an instrument designed and built by a team led by Jack Holt, a professor at the University of Arizona’s Lunar-Planetary Laboratory and Department of Earth Sciences and one of the paper’s co-authors. Holt’s research group specializes in using geophysical survey methods, primarily radar, to study features on Earth and Mars.
ARES was installed on an aircraft as part of Operation IceBridge, a NASA-funded mission tasked with measuring annual changes in the thickness of glaciers, sea ice and ice cover in Greenland, Alaska and Antarctica from aircraft between 2009 and 2021.
As the aircraft traversed the vast expanse of ice, its ice-penetrating radar took an “X-ray” of the glacier, resulting in a full “3D body scan” of the glacier and underlying rock. Measurements have shown that Malaspina Glacier is well below sea level and is cut by several channels in its bed that stretch at least 21 miles from where the glacier meets the shore to its source in the St. Elias Mountains.
The combination of the glacier’s location relative to sea level and the continued loss of its coastal barrier may provide pathways for ocean waters to access large areas of the glacier bed along these channels, the researchers wrote in their paper. Assuming this would result in a large-scale fall of ice masses and glacier retreat, the researchers conclude that Malaspina could drop 560 cubic kilometers, or 134 cubic miles, of ice into the ocean. In other words, Malaspina alone could raise global sea levels by 1.4 millimeters, or just under 1/16 inch.
“That may not seem like much, but to put it into perspective, all Alaskan glaciers together contribute about 0.2 millimeters per year to global sea level rise – a rate that exceeds all other glaciated regions on Earth except for the Greenland and Antarctic ice sheets . Tober said.
According to Tober’s team, the study makes Malaspina the most extensively radar-dated glacier in Alaska. While glaciers in other parts of the world have been mapped with the same level of detail, their counterparts in Alaska have eluded accurate measurements because they are made up of what is known as temperate or “warm” ice.
“There is often water in the crevasses of the glacier, and that makes it difficult to transmit the radar energy to the bottom of the glacier and back to the instrument,” Tober said.
Overcoming this challenge was part of the motivation for creating ARES.
Radar scanning has shown that glaciological models overestimate the volume of Malaspina by more than 30%. However, the glacier, which was just over half a mile thick at its center, boasted a total volume 10 times greater than all the glaciers in the Swiss Alps.
“We can hypothesize that the channels, the big troughs under the glacier, are channeling the meltwater that flows out on the coast,” Tober said.
The observed expanse of lagoons on the Malaspina front over the past few decades has largely alerted a group of researchers, including Holt, to the fact that the coastal barrier in front of Malaspina Glacier is weakening, raising questions about the glacier’s stability. A team consisting of researchers from the University of Arizona, the University of Alaska Fairbanks, the University of Montana and the National Park Service has received a grant from the National Science Foundation to further investigate the potential demise of the world’s largest foothill glacier.
Sydney Mooneyham, co-author of this paper and a graduate of the University of Arizona’s School of Geography, Development and Environment, has mapped the expanse of lagoons on the Malaspina foreland over roughly 50 years of imagery taken by Landsat, a series of Earth observation satellites launched to study and monitor landmass of the Earth.
Another motivation to focus on Malaspina Glacier, Tober said, is that it is located in the largest U.S. national park, Wrangel St. Elias National Park and Preserve. According to the National Park Service, it covers an area of 13.2 million acres, which is larger than Yellowstone National Park, Yosemite National Park and Switzerland combined.
“The potential loss of Malaspina and the opening of a new bay along the Alaskan coastline could be the largest landscape transformation in the US that we could see this century,” Tober said, “and could result in the loss of up to 500 square miles. park land”.