The owner of a Toyota squashed by a 60-ton rock last weekend in Clear Creek Canyon learned a lesson about mountains and gravity.
“If you drive in the mountains, you can’t ignore the hazard of rockfall,” said Ty Ortiz, rockfall program specialist for the Colorado Department of Transportation.
Every day, the Rocky Mountains shed debris – from pebbles to chunks of rock. Fractures or joints in the rock separate, with erosion loosening the rocks.
“Really intense rain like we had last weekend sluices out those pieces of little rocks that are the last straw holding up the big rocks,” said Ed Harp, research geologist with the National Landslide Center in Golden.
“It doesn’t take much to dislodge them since the rock face is slowly eroding,” he added, “becoming a little bit less stable after hundreds and thousands of years.”
The most likely times for rockfalls and slides are in the spring, after freeze-thaw cycles pry open fractures, and during and after significant rain.
U.S. 6 in Clear Creek Canyon west of Golden is high on the list of 756 sites that CDOT scores for rockfall risk.
Factors include slope height and angle, combined with the type and condition of the rock and material between the rocks, and traffic data.
The sites are scattered statewide, usually along mountain corridors, Ortiz said. Georgetown hill on Interstate 70 and Glenwood Canyon join Clear Creek Canyon as higher-risk areas.
CDOT allots $3 million each year to reduce the risk of boulders bouncing on roads, double the amount spent in 2004 and four times what was spent in 1994. More resources are spent on high-traffic areas.
Over a decade, 50 to 60 areas have been treated with high-tech fences, rock bolts, terracing back slopes and mesh drapes. CDOT also does rock scaling to remove loose material.
“We reduce the hazard, but eliminating the hazard is not where we’re at and probably will never be able to completely do,” Ortiz said.
Last year, rockslides caused four highway closures that cost more than $3 million to clean up: I-70 through both Glenwood Canyon and Idaho Springs; U.S. 550 near Paonia; and U.S. 6 through Clear Creek Canyon.
Saturday’s Toyota squishing had a modest price tag: $5,000 to $10,000 – not including the price of the car.
Staff writer Ann Schrader can be reached at 303-278-3217 or aschrader@denverpost.com.
Para leer este artículo en español, vaya a denverpost.com/aldia
