Some info from Supertopo.com:
A very large rock fall occurred from Ahwiyah Point near Half Dome at 5:26 am on the morning of March 28. The rock fall originated near the summit of Ahwiyah Point and fell roughly 1800 feet to the floor of Tenaya Canyon, striking ledges along the way. Debris extended well out into Tenaya Canyon, knocking down hundreds of trees and burying the southern portion of the Mirror Lake loop trail. Reminiscent of the 1996 Happy Isles rock fall, there appears to have been a small airblast associated with impact on the valley floor. Fortunately, due to the event occurring in the early morning, there were no injuries. The impact generated ground shaking that was recorded by numerous seismometers across California, registering as the equivalent of a local magnitude 2.5 earthquake:
http://quake.wr.usgs.gov/recenteqs/Quakes/nc40233925.htm
The volume of the Ahwiyah Point rock fall is still being determined, but it was clearly one of the largest rock falls in the past decade; for perspective this rock fall was many times the size of the recent October 2008 rock falls behind Curry Village. Numerous smaller rock falls have occurred from Ahwiyah Point since the initial failure, and the southern portion of the Mirror Lake loop trail remains closed until further notice.
Greg Stock
Park Geologist
(209) 379-1420
[email protected]
Clarification on closures: The Slabs approach to Half Dome will not be affected by the Southern portion of Mirror Lake loop trail closure. There will be general closure signs, and interpretive signs at the Tenaya Bridge (paved bridge) before the Mirror Lake loop. The Slabs access will remain open.
That said, remember that there has been a lot of rockfall off of the NWF face of Half Dome above the slabs over the last few years. So precede with caution, and consider going the long way through Little Yosemite Valley and up the Half Dome trail.
Another clarification: Peter stated, "Looks like the rockfall will result in a lot more closures around the valley..." This rockfall has not caused any more campground or lodging closures in the Valley. All Yosemite Valley campgrounds are open.
Its great to be back, and I look forward to another season of great threads on the Supertopian forum!
Jesse McGahey
Lead Climbing Ranger
Yosemite Wilderness Management
(209) 372-0360
[email protected]
TCD