Asian glaciers are flowing more slowly in response to widespread ice loss, affecting freshwater availability downstream in India, Pakistan, and China, a new study has suggested.
As part of the study, researchers analysed almost 2 million satellite images of the glaciers and found that 94 per cent of the differences in flow rates could be explained by changes in ice thickness.
For more than a decade, satellite data have documented that the glaciers continue to become thinner as the melt rates on their top surfaces increases.
“It has not been entirely clear how these glaciers are responding to this ice loss. The rate at which they will disappear in the future depends on how they adjust to a warming climate, ” said Amaury Dehecq of NASA’s Jet Propulsion Laboratory in Pasadena, California, who is also the lead author of the study.
Asia’s mountain glaciers flow from the cold heights of the world’s tallest mountains down to warmer climate zones, where they melt much faster, feeding major rivers such as the Indus and Yangtze.
According to researchers of the study, which was published in the Journal of Nature Geoscience, scientists need to understand what is regulating the glaciers’ flow speeds to project how glacial meltwater will contribute to the region’s water resources and to sea level rise.
Observing the glaciers from ground level is difficult because of their huge geographic expanse and inaccessibility, so the researchers turned to satellite images.
“What’s surprising about this study is that the relationship between thinning and flow speed is so consistent,” said coauthor Noel Gourmelen.
In the few locations where glaciers have been stable or thickening rather than thinning, the study found that flow speeds also have been increasing slightly.
The reason a glacier flows down a slope at all is that gravity pulls on its mass. The pull makes a glacier both slide on its base and deform or creep (A slow movement caused by ice crystals slipping past one another under the pressure of the glacier’s weight). As the glacier thins and loses mass, both sliding and creeping become more difficult, and the glacier’s flow slows as a result.