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For decades, the rock glacier slid downhill just a few inches a year, creating small cracks in the road that required only sporadic maintenance.

And Denali scientists have discovered that at Pretty Rocks, a 300-foot stretch sits atop what’s called a rock glacier — ice mixed in with a large amount of rocky debris.

Under a heavy downpour, a chunk of Ritigraben rock glacier broke away, sending waves of debris down to the valley below.

In the last two years alone, scientists have studied the images to track rock glacier movements in Central Asia, shoreline changes in Saudi Arabia, wadi trees in eastern Egyptian deserts and ice loss in Peru.

Larsen’s research reconstructing the Tetons’ glacial history builds on some of those findings because it shows that the Teton Glacier, at least, never disappeared entirely, but rather converted to a rock glacier.