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Another rock fall...

Travelling to and visiting Yosemite National Park. How to get there, what to see or do, and other Yosemite trip advice.

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Another rock fall...

Postby cornbread » Wed Apr 01, 2009 8:45 am

Taken from the Stockton Record's website...

Officials say no one was injured in a giant rockfall near Yosemite National Park's iconic Half Dome, but it did close a trail.

The tumbling boulders unleashed so much fury before daybreak Saturday that it registered as a magnitude-2.5 earthquake. The debris fell into Tenaya Canyon and buried the southern portion of the Mirror Lake loop trail.

Geologist Greg Stock said the avalanche at 5:26 a.m. from Ahwiyah Point was the largest in 10 years, surpassing the October event that forced the park to permanently close part of Curry Village.
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Ahwiyahh Rockfall

Postby dan » Thu Apr 09, 2009 9:20 am

From the NPS news release:
(the webpage above links to 3 photos of the rockfall)

Ahwiyah Point Rockfall Size Estimated
Date: April 8, 2009

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.
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