Rockfalls without an obvious cause (like an earthquake or expanding ice) may be due to hot daily air temperatures expanding small cracks in cliff faces.
The floor of Yosemite Valley is littered with piles of rocks that crumbled off the park’s iconic cliffs. These rockfalls happen all the time, because Yosemite’s granite walls are riddled with cracks produced by geologic stress. Scientists know the rockfalls can be triggered by things like earthquakes, rainfall, and freezing and thawing ice. But many falls occur without an obvious cause. Now researchers think that heat may be the culprit.
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