GLENWOOD CANYON, Colo. (KKCO) - A rock slide as big as the one in Glenwood Canyon is unusual, but in general, rock slides are actually quite common. This is the second one within a 100 mile stretch of I-70 in just a week.
There are many causes for rock slides, from earthquakes to man made triggers like mining and excavation. For the majority of cases in our area, it's the weather that's the main culprit. Late winter, early spring is a time for change. A change in temperatures and rainfall. "Precipitation is very common late winter, early spring as we transition from winter to spring," says Meteorologist Jim Pringle.
Excessive rain fall causes erosion to slowly cut away at the slope and add to that the difference in temperatures during the 24 hour cycle. "When you have these cold days then warmer days then cold days that's what causes these and we have had a lot of rock fall in the area," says Stacie Stegman with CDOT. Daytime highs throughout the canyon have ranged from the upper 40s to mid 50s with some cold nights. "Overnight lows ranging from near 20 to near 30," says Pringle.
It's called the freeze-thaw cycle. Rain falls or snow melts during the day when temperatures are above freezing. Then overnight, the water that doesn't drain away fills the cracks in the rocks, freezes and acts like a wedge, pushing as it expands. "It continues for hundreds and thousands of years to destabilize the slope," says Ed Harp with the U.S. Geological Survey. It's more common than you think. "I would guess thousands a year, many of them never seen," says Harp.
Rock slides that happen near populated areas can cause some severe damage. Many slides happen along roads and interstates as crews cut and blast their way through as they build. "Road cuts tends to cut steeper slopes," says Harp. With the slope cut steep through canyons, rocks have less to hold them up as gravity has a more pronounced effect, constantly pulling down. Keeping crews busy, trying to keep unstable rocks in check. Especially after a fall like the one early this morning in Glenwood Canyon. "There's still a rock that has our geologists worried because it has the potential to come loose," says Stegman. Which will have crews working far beyond just clearing the debris on the road.
While weather is usually the leading cause of the rock slides in our state, you can't rule out earth quakes, which was the cause of a rock slide near palisade just east of Mount Garfield last July.