Beware of rockfalls in warm weather

As the weather warms, watch for falling rocks. While monitoring a cracked cliff in Yosemite National Park, researchers watched the fissure widen as temperatures rose. The risk of rockfalls could increase as climate change cranks the thermostat, one scientist predicts.

For three and a half years, geologists Brian Collins of the U.S. Geological Survey in Menlo Park, Calif., and Greg Stock of the National Park Service in Yosemite monitored a 19-meter-long crack in one of the park’s cliffs. The crack had a maximum width of about 12 centimeters. A measuring device anchored to both sides of the crack recorded changes in its size. The gap grew and shrank by as much as a centimeter daily as temperature changes caused the rock to expand and contract, the researchers report online March 28 in Nature Geoscience. Some effects lingered, however: The gap widened over the course of several summers and the constant size fluctuations further weakened the rock, the researchers say.

Around 25,000 tons of rocks and debris slipped down Yosemite’s slopes in 2015 — enough to fill more than three Olympic-sized swimming pools. About 15 percent of rockfalls from Yosemite’s granite cliffs occur during summer and at the hottest times of day. The rockfall risk could grow along with the cracks as the climate warms, geoscientist Valentin Gischig of ETH Zurich in Switzerland proposes in a perspective piece on the new finding.