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Rockfalls Explained: Yosemite Cliffs Reveal How Heat Causes the Collapse

Jun 02, 2017 12:37 PM EDT
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Rising temperatures increase the danger of cliffs cracking and loose rocks toppling down below. Rockfalls, the fastest type of landslide and characterized by newly detached rock fallind rapidly down a steep slope, can be caused by a number of different factors.

According to a report from Mercury News, heat also plays a huge role in the phenomenon of rockfalls. In a new study of domes and cliffs in Sierra Nevada, researchers discovered that cooler times bring less risk of toppling rocks endangering lives of people and wildlife.

Menlo Park-based U.S. Geological Survey scientist Brian Collins explained and U.S. Park Service geologist Greg Stock analyzed the patterns of 228 previous rockfalls in Yosemite with unknown causes. The pair found out that about 15 percent took place during the hottest time of the day - noon to 6 p.m. - in the warmest months of July to September. Random occurrence would not reach those rates and would be limited to about 6 percent.

The pair also climbed Yosemite's Royal Arches and discovered that during a hot summer afternoon an unstable slab of rock moves off a cliff by eight millimeters. On cool nights, it moves back by seven millimeters.

"Cliffs move in and out, and detach," Collins explained. "People look at landscape as static, that it will be there forever. But it's changing all the time."

Yosemite isn't the only place where rockfalls occur, although the phenomenon hasn't killed a huge number of people - only about 15 people over the past 150 years.

Even the world's majestic mountains like Everest can be vulnerable to such destruction. According to a report from Phys Org, the famous Hillary Step just a few meters from the elusive summit has even already partially collapsed. The Nepal Mountaineering Association has refuted the claim, though.

The study was published in the journal Nature Geosciences.

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