Ok, be honest. What comes to mind when I write the word “exfoliation?” To me, a picture of dry, flaky skin first comes to mind. However, exfoliation has a geological context to it, too. It’s a weathering process and one of the best places to see this process is along Tioga Road in Yosemite National Park.
As you drive that road, take a look at the granite hills and domes all around you. Notice that interesting sort of “onion peel” effect on the rock layers? That’s exfoliation! It’s a type of weathering and is common in granites.
You see, granite formed beneath the earth’s surface, under immense pressure. So, when the surface sediments and rocks – collectively termed as overburden – covering that granite are eroded or removed and that granite is exposed, the pressure beneath which the granite lay is gone and the granite begins to expand, forming all sorts of fractures (joints). Weathering (like frost heaving) causes plates, or flakes of rock to strip away the surface rock much like onion skin peels away from the onion.
And now you know.
Copyright Rebecca L. Latson, all rights reserved.