Sunday, April 5, 2009

Another Look: The Ahwiyah Slide in Yosemite

The Ahwiyah Point rockfall in Yosemite Valley was probably the largest rockfall since 1996, when the Happy Isles fall killed one person and severely damaged the Nature Center (photo here). Luckily the slide a week ago occurred early in the morning so no one was on the trails covered by the event. Access is a bit tricky, but good views of the entire pathway of the slide can be had from the trail north and east of Mirror Lake (the south side of the loop is covered with rockfall debris). Unfortunately (for us geologists) views of the impact area are not so easy; I didn't have time to bushwack across the river, and it was probably still very dangerous in the impact zone anyway.

The first photo shows the entire rockfall zone, from near the top of Ahwiwah Point to the base of the canyon slope on Tenaya Creek. The high rock on the right side is Half Dome, from an angle not often seen by casual tourists (it requires a one and a half mile hike, after all!). The total length of the fall was 1,800 feet.

The second is a zoom on the release point (sorry for the intervening branches; I took about 30 pictures and zoomed only the one time! There were clearer views elsewhere). The nearby trees provide scale; the rock mass was dozens of yards across.

The third and fourth photos provide the only view I could get of the impact zone. Lots of new talus slopes up there, lots of mangled logs, and if you look very carefully at the top of the talus pile, you can see a single tree that survived the onslaught of falling rock.

One more set of photos in the next post!

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