3D Radar Scan Provides Clues About Threats to Alaskan Glacier – ScienceDaily

A detailed survey of the body of Malaspina Glacier, one of Alaska’s most notorious glaciers, revealed that the bulk of it lies below sea level and is eroded by channels that might allow ocean waters to reach, should the coastal barrier erode. This makes the glacier more vulnerable to seawater intrusion than previously thought and may cause it to retreat faster than expected.

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

“The loss of this glacier will likely be the largest loss of ice from an Alaskan glacier this century,” said lead study author Brandon Tauber, a doctoral student in the Department of Geosciences at Arizona State.

The area in front of the Malaspina Glacier, a permafrost with pristine ice below the surface, is “fading away” in the face of rising global temperatures, Tupper said. Permafrost refers to land that remains frozen for two years or more.

“As this coastal barrier erodes and makes way for large lakes, primarily through the collapse of the glacier slopes, ocean water may eventually be able to reach the glacier,” Tupper said. “Once it gets to the front of the glacier, the ice may melt faster and start the glacier’s retreat.”

Malaspina forms a vast ice sheet located directly on the shore of southeastern Alaska. It is the world’s largest piedmont glacier. It is a kind of glacier flowing from steep mountains into a broad plain, basically forming a “pancake of ice” that seeps into a wide area. Coastal plain of 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 these bodies of water expanding over time, forming a lake system directly in front of the glacier over the past few decades.

Researchers have traditionally relied on mathematical models to measure glacier thickness, Topper said, but they differ 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 make predictions about the depth of the glacier, similar to the way river water flow rates are used to gain insights about the depth of a river and the shape of its bed.

“We know that glaciers in Alaska are melting and thinning rapidly in many places, but we don’t know precisely how intense they are, and so we can’t accurately predict future mass loss,” Topper said. “If we didn’t know the thickness and topography of the family, we wouldn’t be able to accurately model their future evolution.”

To get a better idea of ​​Malaspina’s future, the researchers needed to get 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 in the UArisona Lunar and Planetary Laboratory and Department of Earth Sciences, and one of the paper’s co-authors. Holt’s research group specializes in using geophysical research methods, particularly radar, to study features on Earth and Mars.

ARES was installed in aircraft as part of Operation IceBridge, a NASA-funded mission tasked with measuring annual changes in the thickness of glaciers, sea ice and ice sheets in Greenland, Alaska and Antarctica from aircraft between 2009 and 2021.

As the plane criss-crossed the vast icy expanse, its ice-penetrating radar “X-rayed” the glacier, resulting in a full “3D body scan” of the glacier and underlying rocks beneath. Measurements revealed that the Malaspina Glacier lies largely below sea level and is cut by several channels at its bed that extend at least 21 miles from where the glacier meets the shore toward its source in the St. Elias Mountains.

In their paper, the researchers wrote that the combination of the glacier’s position in relation to sea level and the continued loss of the coastal barrier may provide pathways for ocean water to reach large areas of the glacier floor along these channels. Assuming that this leads to widespread icefall and glacier retreat, the researchers concluded 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 1/16th of an inch.

“This may not sound like much, but to put this in perspective, all of Alaska’s glaciers combined contribute about 0.2 millimeters per year to global sea level rise — a rate that eclipses all other glaciers on Earth except for the Greenland and Antarctic ice sheets,” he said. topper.

The study makes Malaspina the most extensive radar-mapped glacier in Alaska, according to Topper’s team. While glaciers have been mapped in other parts of the world with similar levels of detail, their counterparts in Alaska have eluded accurate measurements because they consist of what is known as moderate or “warm” ice.

“Often the glacier’s cracks have water in them, and that makes it difficult to get the radar energy to the bottom of the glacier and back to the instrument,” Topper said.

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

Radar scans revealed that ice models overestimate Malaspina’s size by more than 30%. However, the glacier, which at its center was just over half a mile thick, contained 10 times the total volume of all glaciers in the Swiss Alps.

“We can speculate that the channels, the large basins under the glacier, direct the meltwater that comes out at the coast,” Topper said.

The observed extension of lakes across Malaspina’s territory over the past few decades is largely what has alerted a team of researchers including Holt to the fact that the coastal barrier in front of the Malaspina Glacier is disappearing, raising questions about the stability of the glacier. The team, which consists of researchers from UArizona, the University of Alaska Fairbanks, the University of Montana and the National Park Service, has been awarded a grant from the National Science Foundation to continue investigating the possible demise of the world’s largest Piedmont glacier.

Sidney Moneyham, a co-author of this paper and a graduate of the UArizona School of Geography, Development, and Environment, has mapped the breadth of lakes across Malaspina territory over nearly 50 years from images taken by Landsat, a series of images. Launching Earth observation satellites to study and monitor Earth’s masses.

Another motivation to focus on Malaspina Glacier, Topper said, came from the fact that it’s located in the largest national park in the United States, the 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 bay along the coast of Alaska may be the largest landscape shift within the United States that we can see this century,” said Topper, and it could lead to a loss of up to 500 square miles. from the parkland.”

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