Catching geologic processes in the act can be tricky business. Many are rare and over in a jiffy, so witnessing them is unlikely. Some are so slow you’d never notice them happening, whereas others are too dangerous for observers to get close enough. But lucky for us, an ongoing geological marvel is going on in the Sierra Nevada that someone managed to capture on film.

dotysan/Mika McKinnon/io9

The process is caused exfoliation, which is a form of mechanical weathering in which curved slabs of rock detach and slough off from the rock below, resulting in a so-called exfoliation dome such as Yosemite’s spectacular Half Dome. It’s thought to be the result of “unloading,” whereby overlying rock is removed through erosion or excavation. This releases the pressure and causes the previously-confined rock below to expand, fracturing in the process. Layers of rock are then shed as sheets, leaving a spherical core behind.

While weathering may typically be slow, the ongoing exfoliation at Twain Harte Lake in the Sierra Nevada is really something else. Starting on August 3rd, outcrops of granite have been furiously exfoliating, and one YouTube user, Dotysan, managed to capture it beneath his feet. Check it out here:

[Via Geotripper, ars technica and io9]