Half Dome is one of the most iconic features within Yosemite National Park. Being locating in California, Yosemite is a part of the Sierra Nevada. At some point late July 2 or early July 3, 2015, a large rock fall occurred on Half Dome and permanently altered one of the world-famous climbing routes along the monolith. The rock fall was caused by a process called exfoliation. Exfoliation is caused by the rock expanding due to unloading (the relatively quick release of pressure). Half Dome is part of a huge batholith - a huge collection of underground magma plumes or plutons. As the batholith cooled and crystalized, it was subjected to a tremendous amount of pressure from the overlying rock. Over time the overlying rock was eroded and the batholith was uplifted and exposed at the surface. At the surface, the batholith was no longer exposed to the overlying pressure. As a result, the rock expands and begins to separate like layers in an onion. The rock fall that occurred between July 2 and 3 was a 200 ft. triangle-shaped slab. Luckily no one was injured in the event.
Check out this video by the National Park Service about rockfalls in Yosemite Park