Ahwiyah Point Rockfall Size Estimated
On March 28, 2009, a large rockfall occurred from Ahwiyah Point near Half Dome. Rocks fell roughly 1,800 feet, knocking down hundreds of trees and burying hundreds of feet of trail on the southern portion of the Mirror Lake Loop Trail. The impact generated ground shaking equivalent to a magnitude 2.4 earthquake. Numerous smaller rockfalls have occurred from Ahwiyah Point since the initial rockfall on March 28. There were no injuries or structures affected.
The approximate volume of the initial rockfall is 43,000 cubic meters, or 115,000 tons. This is considerably larger than the 1996 Happy Isles rockfall, which was estimated at 30,000 cubic meters in volume. Therefore, this rockfall is the largest one in Yosemite National Park since the 1987 Middle Brother event.
Due to the debris and trail coverage, the southern portion of the Mirror Lake Loop Trail is closed to hikers indefinitely.
Because of the most recent rockfall activity around Yosemite Valley, there has been speculation that rockfall has become more frequent. Based on historical databases and recent events, park geologists are unable to discern a geologically significant increase in rockfall activity in Yosemite Valley.
Rockfalls are a natural and dynamic geologic process. Due to its steep, glacier-carved cliffs, Yosemite Valley experiences many rockfalls each year. Natural processes like rockfall help to create the beautiful and changing scenery in Yosemite National Park.
Did You Know?
When it opened to the public on May 29, 1926, the Yosemite Museum became the first museum building in the national park system, and its educational objectives served as a model for parks nationwide. It still functions much as it was originally intended, and currently exhibits items which mainly reflect the Native occupation of Yosemite Valley and its surroundings. When in the park, you can visit with one of three cultural demonstrators who primarily staff the Museum.