2013-01-24 / Front Page

Report: 2012 was "quiet" year for rockfall in Yosemite

Last year was relatively quiet for rockfall in Yosemite, according to a report by Park geologist Greg Stock. 

The biggest event of 2012 occurred around 11 p.m. on Jan. 22 above the Big Oak Flat Road. A boulder weighing about 745 tons fell from a cliff above the road, slid down the slope, and struck the Big Oak Flat Road, punching a hole in the eastbound lane, tearing out some of the retaining wall, and severely damaging nearly 100 feet of roadway. The road was closed for about six weeks for repair. 

Consequential rockfalls also occurred from the Church Bowl area, located between Yosemite Village and The Ahwahnee hotel. On April 3 and 4, two nighttime rockfalls occurred from the cliff directly above the popular climbing route “Bishop’s Terrace.” The area beneath the climb was devastated by rock debris, with dozens of trees snapped or toppled by the impacts. Small rocks tumbled all the way to the Valley Loop Trail. Climbing routes in this area were temporarily closed until the cliff stabilized. 

Other areas in Yosemite experiencing rockfall in 2012 include Mirror Lake, El Capitan, Ahwiyah Point, Half Dome, Glacier Point, Elephant Rock, Washington Column, and Hetch Hetchy. 

In all, there were 43 documented rockfalls last year, with an approximate cumulative volume of about 700 cubic meters (about 2,100 tons). Both the number of rockfalls and the cumulative volume for all rockfalls in 2012 are substantially less than that documented in recent years. Although it is not clear exactly why rockfall activity was reduced from previous years, it may relate to the exceptionally dry winter of 2011-2012. 

Geologist Stock said it is very likely that there were additional rockfalls in 2012, but the events either were not witnessed or went unreported. Stock asked Park visitors who witness a rockfall of any size, or encounter fresh rock debris, or hear cracking or popping sounds emanating from the cliffs, to contact him directly at 379-1420 or email greg_stock@nps.gov. 

Predicting rockfall is not yet possible, but understanding the events that do happen is an important step toward the goal, Stock said.

Dust from a rockfall above The Ahwahnee hotel obscures Half Dome in this photo taken in August of 2009. Erik Skindrud / The GAZETTEDust from a rockfall above The Ahwahnee hotel obscures Half Dome in this photo taken in August of 2009. Erik Skindrud / The GAZETTE

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