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Quirks and Quarks

Breaking rocks with the hot sun

Rock fall from cliff faces may be caused by hot temperatures causing stone to expand, swell and break

The Sun may be involved in the catastrophic erosion of cliffs

CBC Radio ·
Dr. Collins and colleague Greg Stock doing vertical research (Valerie Zimmer, US National Parks Service)
Quirks and Quarks8:55Breaking Rocks With The Hot Sun - 2016-04-09 - Pt. 6
Hot summer days could be an unrecognized trigger for catastrophic and dangerous rock falls on cliffs. Geologists have long known that rock-falls in mountainous areas can be triggered by freezing ice opening fractures, or by violent wind and rain-storms, or by earthquakes.

But observations of rock falls in perfect conditions and warm weather led Dr. Brian Collins, a research civil engineer with the US Geological Survey, to look into hot days as an additional trigger. He used specialized tools to measure how cracks opened in the rock during hot days and was surprised to discover that there was considerably more movement than he suspected.

Daytime heating and the resulting thermal expansion of the rock caused cracks to open by as much as a centimetre over the course of a day - as if the cliff was literally breathing. This mechanical cycling likely causes the equivalent of metal fatigue at the points where cracks attach, weakening and opening them a little bit every day until they fail and a rock fall results.

Related Links

- Paper in Nature Geoscience
- US Geological Survey release
- Science news article
- Los Angeles Times article
 

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