Twain Harte rock exfoliation: There is an ongoing geological drama going on the Sierra Nevada that may be unique. The process has been captured on video, and is presently being monitored, due to the effects it is having on a reservoir abutment.
Exfoliation, a process long recognized as the shaper of granitic domes and monoliths, is presently busting up the surface of a small dome at Twain Harte Lake a few miles east of the Mother Lode town of Sonora.
The event burst into the news in August when a possible dam failure warning was issued following a loud popping sound and the leakage of water from the edge of the reservoir. Once the site was investigated, a decision was reached to drain the lake until the full extent of the damage was clear.
No one can say that the episode is over, but it is fascinating to see.
What is exfoliation?
Rock formations are smoothed out into a dome shape through a process called “exfoliation,” in which the top layer of rock sloughs off (and is eventually eroded away) from the lower layers. Like all geological processes, this takes place on a well, geologic time scale, and so is almost never witnessed by people. This guy happened to be in the right place at the right time. AMAZING!
In the Twain Harte’s case, the worry, of course, is the proximity of the exfoliation slabs to the abutment of the dam.