Likely because of its shrinking mass, Yosemite National Park's largest glacier, the Lyell, has ceased its downhill movement, say scientists from the National Park Service and the University of Colorado.
Building on historical research conducted by John Muir and others in Yosemite's history, the research team monitored the Lyell Glacier and the adjacent Maclure Glacier, deep in Yosemite's high country. Movement of the glaciers was monitored by placing stakes in the ice and tracking their positions over a four-year period.
Data collected from stakes placed on the Lyell showed that no movement has occurred at least within the past several years. Earlier research on the glacier showed that it was moving in the 1930s. Stagnation has therefore occurred since that time, perhaps within the past decade. In addition, the Lyell Glacier has decreased in size by about 60 percent since 1900 and has thinned by about 120 vertical feet. This thinning is most likely why the glacier has stopped moving, the researchers say.
The adjacent Maclure Glacier is still moving at its historical rate, about one inch per day.
Glaciers created much of the scenery of Yosemite, including iconic features such as Half Dome. Glaciers are defined as long-lasting ice masses that arise from the accumulation of snow, and move downhill by flowing and sliding.
A glacier's health is determined by the amount of winter snowfall compared with summertime melting of snow and ice. Movement is primarily determined by the glacier's thickness and steepness. Because they are sensitive to environmental conditions, glaciers are important indicators of climate change, scientists say.
"The Lyell Glacier has historically been recognized as the largest glacier in Yosemite National Park and the second largest in the Sierra Nevada," Yosemite National Park geologist Greg Stock said in a news release. "However, the lack of movement suggests that the term 'glacier' no longer accurately describes this feature."
Stock led the investigation along with Robert Anderson of the University of Colorado.