300 glaciers have disappeared from the American West since the mid-20th century – the survivors have a few things in common

A study published in the Proceedings of the National Academy of Sciences found that more than 300 of the roughly 1,450 glaciers present in the contiguous U.S. in the mid-20th century have disappeared entirely, with the total remaining area down 35% from 217 square miles. The fastest thinning is happening in Montana's Beartooth-Absaroka Mountains, losing about a foot and a half of ice thickness yearly, while Washington's larger, cooler glaciers on Mount Rainier and Mount Baker shrink roughly four times slower.

Researchers say the survivors in the Rockies and Sierra Nevada persist mainly because they sit in shaded, avalanche-fed niches rather than because the regional climate favors them, meaning most have little buffer left. The glaciers' retreat also threatens to destabilize steep volcanic moraines in the Cascades, a hazard already linked to landslides that closed highways near Mount Hood and Mount Rainier in 2006.

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