3D radar scan provides clues to threats to Alaska’s iconic glacier

A detailed “body scan” of the Malaspina Glacier, one of Alaska’s most iconic glaciers, has revealed that the bulk of it is below sea level and under channels that may allow ocean water to gain access if its coastal barrier erodes. This makes the glacier more vulnerable to seawater intrusion than previously thought and may cause it to retreat faster than predicted.

The findings, published by researchers at the University of Arizona in Journal of Geophysical Researchthey highlight the fragility of a very large glacier system that could lead to the loss of a significant volume of National Park Service ice and land and contribute a measurable amount to global sea-level rise.

“The loss of this glacier would probably be the largest loss of ice from an Alaskan glacier this century,” said study lead author Brandon Tober, a doctoral student in Arizona’s Department of Geosciences.

The area in front of Malaspina Glacier, a permafrost zone with pure ice below the surface, is “losing” 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 steep ice cliffs, ocean water can eventually gain access to the glacier,” Tober said. “Once it reaches the front of the glacier, it can melt the ice even faster and start the retreat of the glacier.”

Forming an extensive ice sheet located just off the coast of southeast Alaska, Malaspina is the world’s largest Piedmont glacier, a type of glacier that flows from steep mountains into a wide plain, essentially forming an “ice pancake” that spills into a large coastal plain. plain from the mountains of Agios Ilias. A thin barrier of land separates the glacier from the relatively warm waters of the Gulf of Alaska. Historical satellite images show these bodies of water expanding over time, forming a lagoon system directly in front of the glacier in recent decades.

Traditionally, researchers rely on mathematical models to measure 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 on the surface to make predictions about glacier depth, similar to how a river’s water flow rates are used to gain insights into depth and shape of his bed.

“We know that glaciers in Alaska are melting and thinning rapidly in many places, but we don’t know exactly how thick it is, so we can’t accurately predict future mass loss,” Tober said. “If we don’t know the thickness and topography of the bed, we can’t accurately model their future evolution.”

To get a better idea of ​​Malaspina’s future, the researchers needed to do a detailed “body scan” of its shape and thickness. To do this, Tober’s research team used the Arizona Radio Echo Sounder, or ARES, an instrument designed and built by a team led by Jack Holt, a professor in the UArizona Lunar and Planetary Laboratory and Department of Geosciences, and one of the partners of the newspaper. -writers. Holt’s research group specializes in using geophysical survey methods, primarily radar, to study features on Earth and Mars.

ARES was mounted on an aircraft as part of Operation IceBridge, a mission to measure annual changes in the thickness of glaciers, sea ice and ice sheets in Greenland, Alaska and Antarctica from aircraft between 2009 and 2021.

While the plane traversed the vast, frozen expanse, its ice-penetrating radar “X-rayed” the glacier, resulting in a full “3D body scan” of the glacier and underlying rock. The measurements revealed that Malaspina Glacier is largely below sea level and is cut by several channels in its bed that stretch at least 21 miles from where the glacier meets the coast to its source in the Saint Elias Mountains.

The combination of the glacier’s position relative to sea level and the ongoing loss of its coastal barrier may provide pathways for ocean waters to access large areas of the glacier floor along these channels, the researchers write in the paper their. Assuming this leads to large-scale shedding of ice masses and glacier retreat, the researchers conclude that Malaspina has the potential to contribute 560 cubic kilometers, or 134 cubic miles, of ice to the ocean. In other words, Malaspina alone could raise global sea levels by 1.4 millimeters, or just under 1/16 of an inch.

“That may not sound like much, but to put it in perspective, all of Alaska’s glaciers combined contribute about 0.2 millimeters per year to global sea level rise – a rate that exceeds all other glaciated areas on Earth except from the Greenland and Antarctic ice sheets. Tober said.

The study makes Malaspina the most extensively radar-mapped glacier in Alaska, according to Tober’s team. While glaciers in other parts of the world have been mapped with similar levels of detail, their counterparts in Alaska have eluded precise measurement because they are made of what is known as temperate or “warm” ice.

“Glacier crevasses often have water in them, and that makes it difficult to transfer radar energy down the glacier bed and back to the instrument,” Tober said.

Overcoming this challenge was part of the motivation for building ARES.

Radar scans revealed that glaciological models overestimate the volume of Malaspina by more than 30%. However, the glacier, which was measured to be just over half a mile thick at its center, boasts 10 times the combined volume of all the glaciers in the Swiss Alps.

“We can assume that the channels, the large troughs under the glacier, are channeling the meltwater that comes out to the coast,” Tober said.

The observed extent of lagoons across the front of Malaspina in recent decades is largely what has alerted a team of researchers, including Holt, to the fact that the coastal barrier in front of Malaspina Glacier is disappearing, raising questions about its stability. glacier. The team, which consists of researchers from UArizona, the University of Alaska Fairbanks, the University of Montana and the National Park Service, received a grant from the National Science Foundation to further investigate the possible collapse of the world’s largest Piedmont glacier.

Sydney Mooneyham, a co-author on this paper who graduated from UArizona’s School of Geography, Development and Environment, mapped the extent of lagoons across the Malaspina foreland over nearly 50 years of images taken by the Landsat, a series of earth observation satellites launched to study and monitor the Earth’s land masses.

Another motivation to focus on Malaspina Glacier, Tober said, came from the fact that it is located in the largest national park in the US, Wrangell Saint Elias National Park and Preserve. At 13.2 million acres, it’s larger than Yellowstone National Park, Yosemite National Park and the country of Switzerland combined, according to the National Park Service.

“The potential loss of Malaspina and the opening of a new gulf along the Alaskan coastline may be the largest landscape transformation in the US that we could see during this century,” Tober said, “and may lead to loss of up to 500 square miles. of the land in the park.”