3D radar scan provides evidence of threats to iconic Alaska glacier – Zoo House News

3D radar scan provides evidence of threats to iconic Alaska glacier – Zoo House News

  • Science
  • March 19, 2023
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A detailed “body scan” of Malaspina Glacier, one of Alaska’s most famous glaciers, revealed that much of it lies below sea level and is undercut by channels that could allow seawater access should its coastal barrier erode. 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 University of Arizona researchers in the Journal of Geophysical Research, underscore the fragility of a very large glacial system that could result in the loss of a significant volume of National Park Service ice and land, and would contribute a measurable volume to the global Sea level rises.

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

The area in front of the Malaspina Glacier, a permafrost zone with pure ice beneath the surface, is “disappearing” as global temperatures rise, Tober said. Permafrost refers to soils that remain frozen for two or more years.

“As this coastal barrier erodes to give way to large lagoons, primarily from ice cliff collapse, ocean water may eventually gain access to the glacier,” Tober said. “Once it reaches the face of the glacier, it can melt the ice even faster and start glacier retreat.”

Forming an extensive ice sheet 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 spreads to a latitude gushes 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 imagery shows that these waters expanded over time, forming a lagoon system just in front of the glacier in recent decades.

Traditionally, researchers have relied 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 across the surface to make predictions about the depth of the glacier, much like the water flow rates of a river are used to gain insight into its depth and the shape of its bed.

“We know that Alaskan glaciers are rapidly melting and thinning 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 don’t know the thickness and layer topography, we can’t accurately model their future evolution.”

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

ARES was launched 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 mounted plane.

As the plane criss-crossed the vast, icy expanse, its ice-penetrating radar “scanned” the glacier, resulting in a full “3D body scan” of the glacier and underlying bedrock. Measurements revealed that the Malaspina Glacier lies mostly below sea level and is bisected at its bed by several channels 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 location in relation to sea level and the ongoing loss of its coastal barrier could provide pathways for ocean water to access large areas of the glacier bed along these channels, the researchers write in their article. Assuming this will result in 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 inch.

“That 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 exceeds all other glaciated regions on Earth except for the ice sheets surpassed by Greenland and Antarctica,” 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 Alaskan counterparts eluded accurate measurements because they are composed of so-called temperate, or “warm” ice.

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

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

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

“We can speculate that the channels, the large hollows beneath the glacier, channel meltwater that exits the coast,” Tober said.

The wideness of Malaspina foreland lagoons observed over the past few decades was largely what drew a team of researchers, including Holt, to the attention of the fact that the coastal barrier in front of the Malaspina Glacier is receding, 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 further investigate the possible sinking of the world’s largest Piedmont glacier.

Sydney Mooneyham, a co-author of this article, who is a graduate of the UArizona School of Geography, Development and Environment, mapped the expanse of the Malaspina Foreland Lagoons over about 50 years using Landsat imagery, a number of earth observation satellites will be launched to study and monitor the earth’s landmasses.

Another motivation to focus on Malaspina Glacier, according to Tober, is the fact that it’s located within the largest national park in the United States, Wrangell Saint Elias National Park and Preserve. At 13.2 million hectares, it’s larger than Yellowstone National Park, Yosemite National Park, and Switzerland combined, according to the National Park Service.

“The potential loss of Malaspina and the opening of a new bay along the Alaskan coast could be the largest U.S. landscape change we have seen this century,” Tober said, “and it could result in the loss of up to 500 square miles of.” parkland.”

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