Park Officials have now estimated the size of a recent Yosemite rockfall that was big enough to register on earthquake scales.

On March 8, 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.

Many smaller rockfalls have occurred from Ahwiyah Point since the initial rockfall on March 8. There were no injuries or structures affected.

Park Officials say that the approximate volume of the initial rockfall was 43,000 cubic meters, or 115,000 tons. This is considerably larger than the 1996 Happy Isles rockfall, estimated at 30,000 cubic meters in volume, making this the largest rockfall in Yosemite National Park since 1987.

Due to the debris and trail coverage, the southern portion of the Mirror Lake Loop Trail is closed to hikers indefinitely.

Park Officials say that the recent rockfall activity around Yosemite Valley, including the slides near Curry Village, have caused speculation that rockfall has become more frequent. Based on historical databases and recent events, park geologists dont see a geologically significant increase in rockfall activity in Yosemite Valley.

Park Officials say rockfalls are a natural and dynamic geologic process. Due to the 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, according to Park Officials.


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