YOSEMITE -- For thousands of years, slabs of the Glacier Point cliff have broken loose, roared down at more than 100 mph and blasted the forest in nature's version of bunker bombs.
Such rockfalls are triggered by earthquakes, large storms or freezing and thawing of water in granite joints. But are these frightening events also somehow connected to the toilets at the Glacier Point overlook above the sheer cliff? Did water from the septic system drain into the cliff face and cause a 1999 rockfall that killed a climber?
One geologist thinks so. His views have been disputed by government agencies and challenged by other geologists. But this wastewater theory also is touted as possible proof of negligence in a lawsuit against the National Park Service over the death nine years ago of Peter Terbush, 21, of Gunnison, Colo.
The situation also raises an old issue in national parks -- the difficulty of protecting the public in a place filled with natural hazards.
No matter how the legal and scientific debates end, an increase of large Glacier Point rockfalls has raised concern at Yosemite National Park. On Oct. 7 and 8, a rockfall destroyed one visitor cabin at Curry Village and damaged many others, prompting an evacuation involving about 1,000 visitors.
The October rockfalls were among a series of such events spread over the last decade around Curry Village, where large rockfalls had not been regularly seen for many years.
Officials have ordered demolition of almost 300 Curry buildings within the rockfall landing area, including 233 visitor cabins. That's nearly half of the buildings in the area.
The Curry closures may be the only point of agreement between government scientists and geologist Chester F. "Skipp" Watts, who has been advocating the wastewater theory for a decade and asking for more safety measures.
"I think public safety is finally on the radar screen," said Watts, a professor and chairman of the geology department at Radford University in Virginia.
Watts, who specializes in highway and mining slope stability study, climbed the rock face with other researchers in the 1990s to investigate rockfalls.
He said joints in the Yosemite granite can act as conduits for water to flow downward, create pressure on slabs of granite and force them to break free. He said he traced such joints from two rockfall sites up to Glacier Point wastewater facilities.
Watts said he linked a large 1996 rockfall at nearby Happy Isles to the leach field for bathrooms. He traced another to where a Park Service water supply for restrooms was allowed to pour out for more than two months.
Watts said the Park Service water is connected to an increase in Glacier Point rockfall since in the last 12 years. Two people died as a result of rockfalls in 1996 and 1999.
"We have a timeline graph that shows a correlation with rockfall," he said. "It is clear. When some of these events happened in the last 10 years, wastewater is being released." Park geologist Greg Stock and others dispute the notion, saying there are no scientific findings to support it.
Stock said no trigger has been discovered yet for the October rockfalls. Though water can make rockfalls happen, there was no water involved, he said.
Stock added that rockfalls have been occurring for at least 15,000 years. Yosemite Valley is surrounded by sheer, glacially carved cliffs. It is often difficult to pin down the exact trigger, and no one can predict when one section of the cliffs will become more active.
There may have been a lull in large rockfall near Curry Village for many decades, Stock said. But from the millions of tons of debris at the base of the cliff, it is clear that the events are a regular part of the geologic history.
The closure of guest cabins and other Curry buildings is not related to Watts' theory, Stock said. The Park Service is reacting to rockfall that has damaged cabins in the last several years.
He said the Park Service acknowledges that the Curry buildings should not remain on the mound of granite debris, known as a talus slope.
"Most of those cabins date back to the 1920s and 1930s when there was a different concept of safety," he said. "Many of those cabins were positioned on the active talus slope." Other scientists say Watts' research has left too many questions unanswered, and they criticize a lack of publication in a scholarly journal.
Geologist L. Scott Eaton, an associate professor at James Madison University in Virginia, said Watts needed to test the water on a cliff to see if it is from a wastewater system.
"They should be able to test for things like nitrate, estrogen, caffeine," he said. "I have not seen this work published in any peer-reviewed publication."
Geological engineer Nicholas Sitar, a professor at the University of California, Berkeley, said more than 95 percent of the water at Glacier Point comes naturally from snowmelt and precipitation. Wastewater accounts for only 3.5 percent of the water at Glacier Point.
He said the huge difference in the numbers makes it hard to believe wastewater could be the main trigger of rockfall.
"We do not think there is much to Professor Watts' position," he said.
Sitar has been hired by the U.S. Department of Justice as an expert witness for the federal government in the climber case, which was filed by the family of Terbush.
The case was dismissed three years ago in U.S. District Court in Fresno. The court ruled the Park Service has legal discretion to decide whether to post warning signs at the base of the wall where the climber was killed. There were no signs posted.
Yosemite officials said there is rock poised to fall all around the towering walls of Yosemite Valley. There is a degree of rockfall danger throughout the seven-square-mile area.
Officials said they do warn people away from known high-risk areas.
They also close active rockfall areas, such as the Curry Village buildings. But there is no way for the Park Service to manage all the risk in the valley, officials said.
A federal appeals court in San Francisco upheld the dismissal. The case was returned to the Fresno district court to determine if the Park Service was legally maintaining the wastewater system at Glacier Point.
A research report from Watts is scheduled to be entered into the court record this month. The court has scheduled motions on the case in late September 2009.
Fresno Bee reporter
Mark Grossi can be reached at firstname.lastname@example.org or (559) 441-6316.