|El Capitan and the September rockfall from Taft Point on Oct. 29, 2017|
|September rockfall from Taft Point on Oct. 29, 2017|
According to Greg Stock, geologist for Yosemite National Park, the biggest slab (out of seven total), was 394 feet long, 148 feet wide, and between 8 and 28 feet thick. That's bigger than a football field. It had a volume of 10,250 cubic meters, and weighed about 27,675 metric tons. If these numbers and dimensions seem incredibly exact, there's a reason. As Greg Stock explains, in an informative research paper, the walls have been mapped in three dimensions by a form of radar (lidar), and in the aftermath of the rockfall, the walls at the site of the fall were mapped again. The difference in volume could then be calculated.
|El Capitan from Taft Point in 2005|
I was at Taft Point in 2005, taking pictures of course, and one can compare the appearance of the cliff prior to the event in September.
|Horsetail Falls area and future site of rockfall in 2005|
|The Horsetail Falls cliff on Oct. 29, 2017|
|The cliff near Horsetail Falls in 2016|
|El Capitan and the Horsetail Falls cliff on October 30, 2017|
As I was going through my old pictures, I came to realize that slides have come off this particular cliff in the past. I actually witnessed one of them in 2010 when I was lounging on the granite near the top of Sentinel Dome across the valley. When I say "witnessed" I mean I heard the commotion first, took a moment to realize what I was hearing, jumped up, scanned up and down the valley, and finally thought to turn on the camera and take a few pictures of the rising dust plume.
|Dust plume from the 2010 rockfall east of El Capitan|