3D radar scan provides clues about threats to iconic Alaskan glacier – ScienceDaily

A detailed “body scan” of Malaspina Glacier, one of Alaska’s most iconic glaciers, revealed that most of it lies below sea level and is undercut by channels through which ocean water could gain access should the coastal barrier erode. This makes the glacier more vulnerable to seawater intrusion than previously thought and could cause it to retreat faster than predicted.

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

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

The area in front of the Malaspina Glacier, a permafrost zone of pure ice below the surface, is “withering away” in the face of rising global temperatures, Tober said. Permafrost refers to soil that remains frozen for two or more years.

“As this coastal barrier erodes and gives way to large lagoons, mainly due to the collapse of ice cliffs, ocean water may eventually access the glacier,” Tober said. “Once it reaches the front of the glacier, the ice could melt even faster and trigger glacier retreat.”

Forming a vast ice sheet right off the coast of Southeast Alaska, Malaspina is the world’s largest Piedmont Glacier, a type of glacier that flows from craggy mountains to a broad plain, essentially forming a “pancake of ice” that tapers into a wide coastal plain of the St. Elias Mountains. A thin land barrier separates the glacier from the relatively warm waters of the Gulf of Alaska. Historic satellite images show that these bodies of water expanded 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 over the surface to make predictions about the glacier’s depth, similar to how a river’s water flow rates are used to understand the depth and shape of a glacier. the bottom.

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

To get a better idea of ​​Malaspina’s future, the researchers had to take a detailed “body scan” of its shape and thickness. To do this, Tober’s research group used the Arizona Radio Echo Sounder, or ARES, an instrument designed and built by a team led by Jack Holt, a professor at the UArizona Lunar and Planetary Laboratory and Department of Geosciences, 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 mounted on an aircraft as part of Operation IceBridge, a NASA-funded mission to measure from aircraft the annual changes in the thickness of glaciers, sea ice and ice sheets in Greenland, Alaska and Antarctica between 2009 and 2021.

As the plane criss-crossed the vast, icy expanse, its ice-penetrating radar “beamed” the glacier, resulting in a full “3D body scan” of the glacier and underlying bedrock. The measurements showed that the Malaspina Glacier lies mostly below sea level and is intersected by several channels at the bottom that extend at least 34 kilometers from where the glacier meets the coast to its source in the Saint Elias Mountains.

The combination of the glacier’s location relative to sea level and the continued loss of the coastal barrier may provide avenues for ocean waters to access large areas of the glacial floor along these channels, the researchers write in their paper. 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 of ice to the ocean. In other words, Malaspina alone could raise global sea levels by 1.4 millimeters.

“This may not sound like much, but to put this into perspective, all of Alaska’s glaciers collectively contribute about 0.2 millimeters per year to global sea level rise — a rate that exceeds all other glacial areas on Earth apart from the Greenland ice sheets. and Antarctica.” Tobert 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 to similar levels of detail, their Alaskan counterparts have escaped accurate measurement because they are made up of what is known as temperate or “warm” ice.

“The crevasses of the glacier often contain water, and that makes it difficult to get radar energy to the bottom of the glacier and back to the instrument,” Tober said.

Overcoming that challenge was part of the motivation to build ARES.

The radar scans showed that glaciological models overestimated the volume of Malaspina by more than 30%. Yet the glacier, which was measured to be just over half a mile thick at its center, has 10 times the total volume of all the glaciers in the Swiss Alps.

“We can speculate that the channels, the large troughs under the glacier, are channeling meltwater coming in from the coast,” Tober said.

The perceived expanse of lagoons across the Malaspina foreland in recent decades is largely what prompted a team of researchers, including Holt, that the coastal barrier in front of the Malaspina Glacier is languishing, raising questions about the stability of the glacier. The team, which includes 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 investigate the possible demise of the world’s largest glacier in Piedmont. to investigate.

Sydney Mooneyham, a co-author of this paper who graduated from the UArizona School of Geography, Development and Environment, mapped the vastness of the Malaspina foreland lagoons over the course of about 50 years of photographs taken by Landsat, a series of Earth observation satellites launched to study and track the Earth’s land masses.

Another motivation to focus on the Malaspina Glacier, Tober said, came from the fact that it’s located in the largest national park in the U.S., the Wrangell Saint Elias National Park and Preserve. At 13.2 million acres, it is 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 bay along the Alaskan coastline may be the largest U.S. landscape transformation we could see in this century,” Tober said, “and it could lead to the loss of as many as 500 square miles of park land.”

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