SOURCE: Alaska Dispatch News

DATE: September 19, 2017

SNIP: A study of rock avalanches in the western part of Glacier Bay National Park and Preserve found that the likelihood of large slides covering about 2 square miles has at least doubled in the last five years. As the climate has warmed, characteristics of the region’s rock avalanches have changed, says the study, published in Landslides, the journal of the International Consortium on Landslides.

“They’re bigger, and they’re traveling farther,” said lead author Jeffrey Coe, a U.S. Geological Survey landslide expert based in Colorado.

The likely reason, says the study, is thaw of the ice that fills the mountains’ rock cracks, crevices and fractures, referred to as “rock-permafrost,” abetted by melt of the region’s glaciers and the particular structures of the slopes.

The rock-permafrost helps hold steep slopes intact, so thaw or even softening of that ice destabilizes the rock, Coe said. “You can get ice degradation below freezing,” he said.

Glacial thinning is likely a secondary factor, he said. Thinned glaciers are less effective at propping up mountain faces, he said. “In many places, you have a de-buttressing effect of the ice loss,” he said.

The study correlates the increasing size of Glacier Bay rock avalanches to a long-term warming trend. The large avalanches began about two years after the area’s annual maximum temperature shifted above freezing, the study points out.