The most recent rockfalls from Glacier Point in Yosemite National Park are not the first to shower Curry Camp and certainly won't be the last. With that in mind, geologists are taking a close look at Glacier Point to try to determine just how safe, or unsafe, its rock face is.

The geologists, from both the National Park Service and the U.S. Geological Survey, are expected to present their findings later this fall to Yosemite Superintendent Mike Tollefson, who will have to decide whether all of the Camp Curry tent village can reopen to visitors.

It was just last week when two rockfalls from Glacier Point rained down on the village. The second, about 7 a.m. on October 8, impacted about ten tent- and hard-walled cabins in Camp Curry and left some park visitors with relatively minor injuries. While the entire camp initially was closed, currently only about 100 of the units remain closed while the geologists study Glacier Point.

Yosemite spokesman Scott Gediman says a report is probably at least two or three weeks away. Once it's finished, it will go to Superintendent Tollefson, who will decide whether to fully reopen Camp Curry or if some areas should be permanently closed out of safety concerns.

"We have over 100 closed now, but obviously the safet of the park visitor is the utmost concern," says the ranger.

Rockfalls are not new in the Yosemite Valley. According to a 2007 USGS report, more than 500 rockfalls have been reported in the valley between 1857 and 2004.

Since 1857, various types of landslides, particularly rockfalls, rockslides, and debris flows have been observed in Yosemite Valley by many visitors, including Josiah Whitney, the first State Geologist of California; James Hutchings, author and hotel owner in Yosemite; John Muir, noted naturalist; and Joseph LeConte, Professor of Geology at the University of California. More systematic recording of both small and large rockfalls and other types of landslides affecting facilities began after 1916 in the monthly National Park Service Superintendent’s reports. The level of rockfall documentation increased beginning in the 1980s with the involvement of the U.S. Geological Survey with the NPS and others.

Between 1857 and 2004, 14 people have been killed and at least 62 injured by more than 541 landslides that have been documented in Yosemite National Park. Some landslides in Yosemite have been observed during rainstorms, earthquakes, or other natural triggering events. However, most landslides in Yosemite have not been directly observed when they occurred, and many of their triggers are unknown.

For example, although infiltrating rainfall is not literally observed filling rock joints, time coincidence of storms and rockfall might result from increased ground-water pressure that destabilizes a jointed rock mass. In many cases, even though a rockfall was closely observed, no specific trigger was recognized. For example, on August 6, 1870, Joseph LeConte saw a very large rockfall from Glacier Point but did not observe a storm, earthquake, or other trigger. During the period of 1857 to 1992, 54 percent of landslides had unreported or unrecognized triggers. Using a 1992 rockfall database and hazard assessment, geologists have tried to achieve a better scientific understanding of Yosemite landslide failures by more detailed study of individual events. Near Glacier Point in Yosemite Valley, as many as 58 rockfalls, rockslides, and debris flows were recorded between 1870 and 2004, some of which have adversely affected infrastructure at Curry Village.

Most recently, there were substantial Glacier Point rockfalls in 1999, which resulted in the fatality of Peter Terbush, a climber who refused to seek safety and instead maintained a belay on a partner; 2000, and 2003. The 2003 rockfall, which impacted 16 cabins in Curry Village and spurred the USGS report, led to the permanent closure of seven cabins, according to Ranger Gediman.

While the geologists are using high-end digital photography to help analyze the stability of Glacier Point's face, "all the science in the world may not tell us, will not tell us when the next rockfall will occur," he says.

Indeed, here's the conclusion from that 2007 USGS report:

Analysis of numerous historic landslides in Yosemite National Park has indicated that unpredictable landslides might occur in many regions, especially within Curry Village in Yosemite Valley. Geologic conditions including post glacial weakening of bedrock, joint spacing and orientation within cliffs, and groundwater infiltration and pore pressure development from cold weather conditions have influenced the triggering of rockfalls, rockslides, and debris flows. Examination of recent landslides and subsurface trenches in the western section of Curry Village has indicated that in some places landslide deposits extend further than the current talus slopes above Curry Village, thus facilities are more vulnerable to landslide hazards than originally assumed.