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Yosemite's granite cliffs are 'breathing,' and heat can make them fall (LATimes)
The domes and arches etched into Yosemite's famed granite cliffs may seem frozen in time, but in reality they're constantly moving.
The dramatic rock formations were formed as layers of rock peeled away from the mountainside, like an onion. The flakes remain attached at a few points but are completely hollow in the middle. If you were to pound on one with your fist, you’d hear an echo.
In Yosemite, these precarious attachments – geologists call them “exfoliations” – fall at a rate of one a week, on average. Most often, they collapse because water repeatedly freezes and thaws in the cracks, destabilizing the cliffs. Sometimes they fall apart during an earthquake.
Other times though, rockfalls happen on sunny days with no sign of rain or seismic activity. Now geologists from the U.S. Geological Survey and the National Park Service have found a potential cause for the seemingly spontaneous rockfalls: heat.
---Snip---
The dramatic rock formations were formed as layers of rock peeled away from the mountainside, like an onion. The flakes remain attached at a few points but are completely hollow in the middle. If you were to pound on one with your fist, you’d hear an echo.
In Yosemite, these precarious attachments – geologists call them “exfoliations” – fall at a rate of one a week, on average. Most often, they collapse because water repeatedly freezes and thaws in the cracks, destabilizing the cliffs. Sometimes they fall apart during an earthquake.
Other times though, rockfalls happen on sunny days with no sign of rain or seismic activity. Now geologists from the U.S. Geological Survey and the National Park Service have found a potential cause for the seemingly spontaneous rockfalls: heat.
---Snip---
http://www.latimes.com/science/sciencenow/la-sci-sn-yosemite-rockfalls-heat-20160328-story.html
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