Alaska is the home of the world's biggest piedmont glacier - meaning it falls from a mountain into a flat plain. But a new study has revealed that the Malaspina Glacier is not quite as big as previously believed, and that its low elevation makes it more highly susceptible to melting that would affect the rise in global sea levels.

The glacier spills out of the St. Elias Mountains into a wide circular lobe atop a broad plain that stops short of the sea. At its widest, the glacier spans 40 miles across. It's located about midway between Yakutat and Icy Bay, where Southeast Alaska connects with the rest of the state.

The study, led by University of Arizona scientists and published in the Journal of Geophysical Research, used specially designed radar devices to conduct what was, in effect, a full-body scan that penetrated down to Malaspina's base, including into the bedrock underlying it.

It found that Malaspina' s ice volume is about 165 cubic miles, about 30% smaller than prior estimates. Two-thirds of the glacier is grounded below sea level, and those bottom portions of the glacier are undercut by several channels running as deep as 1,150 feet below sea level, the study found.

At the same time, the land barrier that separates Malaspina from the ocean is shrinking as lagoons on it expand. Earlier research by the National Park Service, University of Arizona and University of Alaska Fairbanks indicates that saltwater is already encroaching through that dwindling land barrier and that Malaspina may be transitioning into what is known as a tidewater glacier.

Exactly when and how fast Malaspina will melt out is a subject still being calculated, said the study's lead author, Brandon Tober, a University of Arizona geophysics doctoral student. That work is being done by the same team that produced the new study, with members from UAF and the University of Montana as well as Tober and his University of Arizona colleagues. Tober said he hopes some results that forecast Malaspina's future will be ready for release by the end of the year.

The Malaspina-scanning research was part of NASA's Operation IceBridge, a program that ran from 2009 to 2021 and used airborne equipment to measure sea ice, glaciers and ice caps in both polar regions.

Generally, glacier volume measurements are made through calculations from afar that factor in the physics of locations and movement over time. But those calculations are just estimates, Tober said.

"Really, the main way to figure it out is to go fly over them with radar and measure," he said.

A challenge to radar measurements of Alaska glaciers is that in this temperate latitude, the ice is considered warm, which means it holds pools and pockets of water. That liquid water often absorbs the radio waves used by radar, interfering with any measurement attempts. To address that problem, this Malaspina project used extremely low-frequency waves that were able to penetrate those sections of liquid water, Tober said.

Most of the data for the study came from flights done in 2021, completing a grid pattern over the glacier, but there is use of data collected as far back as 2013, he said.

Alaska holds much less than 1% of the world's glacial ice, but Alaska glaciers are outsized contributors to global sea-level rise, which is largely the product of meltwater from land ice, including glaciers and ice sheets, and thermal expansion as the oceans get warmer and their waters take up more space.

Alaska glaciers contribute more than any other source of land ice aside from the Greenland and Antarctic ice sheets, according to various recent studies that put Alaska glaciers' contributions at around 6% or 7%.

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