Yes, Glaciers Melt, But Do You Know How?
Perito Moreno Glacier calving (Sean Munson/Flickr)

Have you ever wondered how glaciers melt? Do they melt from underneath? Top down? Maybe from all around at once? From the center outward? How fast do they melt? Do all glaciers melt? These are questions scientists’ wonder too, and they’ve been getting some interesting answers.

Virtually every glacier on earth melts each year during the summer, but as long as winter snow accumulation is equal to or greater than that summer melt, a glacier is considered to be stable or growing. If the glacier melts more in the summer than it grows in the winter however, it retreats. But exactly how glaciers melt has not been understood in a comprehensive manner. What is known is that glacial ablation can be caused by any number of natural forces: wind, sun, rain, fauna, evaporation, sublimation and every other possible fashion one could imagine removing a chunk of ice from a even larger chunk of ice.

One of the most talked about forms of glacial ablation is glacial calving. Icebergs, for instance, are created when a chunk of glacier breaks off (or calves), usually falling into the body of water to which it drains. Calving often occurs from a process of erosion at the water line. Calving has gotten attention lately because of new evidence showing that for some glaciers, warmer ocean temperatures have been inarguably increasing the rate of glacial erosion underneath the water line. “Researchers found that, for some ice shelves, melting on its underbelly could account for as much as 90 per cent of the mass loss,” according to research published in Nature in September of last year. This aspect of glacial melt that was not previously well understood, but calving and ocean erosion are not the whole story to glacial ablation.

In 2008, Natalie Kehrwald, a Ph.D. student at Ohio State University, was attempting to date ice cores she drilled from a glacier in Tibet twenty thousand feet above sea level by searching for particular radioactive isotopes found all over the world from the mid-20th Century U.S. and Soviet Union atomic testing. She soon realized she couldn’t find the isotopes she was looking for. Confused, she used a different technique to date the top-most layer of the ice cores, and discovered that the newest ice in the samples dated from the 1940s. Kehrwald inadvertently proved that glaciers at those elevations in the Himalayas melt from top to bottom. Of course, it was the first time anyone had observed such a phenomenon, and it doesn’t mean top-down is the only way mountain glaciers melt.

At the Sandy Glacier on Mount Hood in Oregon, two climbers have discovered another particularly fascinating way glaciers melt. Brent McGregor and Eddy Cartaya have been exploring a system of glacial caves that extend more than 7,000 feet inside the glacier. Beautifully sculpted on the inside and ready-made for adventure, these glacier caves are significant because they exhibit glacial melt that is otherwise difficult to document. Scientist sometimes use satellites to record glacial melt, but those techniques would not perceive internal loss occurring within a glacier, as in the ice caves on Mount Hood. Andrew Fountain, a glaciologist at Portland State University, said he didn’t know of any effort to track how much the ice inside a glacier melts from year to year, before learning of the Sandy cave system, according to a recent Oregon Public Broadcasting article on the discovery.

Studying the many different ways the world’s glaciers can melt may help the scientific community better understand how to prevent them from disappearing.

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