Massive landslide even amazes CDOT geologist

The landslide that complicated the lives of so many travelers on Interstate 70 during the holiday weekend was so massive and unusual it even amazed a geologist who helped build the road.Rick Andrew said the landslide was a “really large, very unusual, rare event.” Such occurrences, he said, are referred to as “100-year events” because the probability of their happening is so low.Andrew is a former staff geologist and current consultant with the Colorado Department of Transportation. He helped determine the location of retaining walls and other mitigation measures when the four-lane interstate was built through the canyon in the 1980s.Andrew said there was no way to anticipate Thursday’s slide. It wasn’t a case of rocks becoming dislodged from dirt and rolling down a dirt slope. Instead, quartzite broke off a sheer cliff a half-mile west of the Hanging Lake Tunnel.

“If you think about a glacier calving off – that’s what this was like,” he said. The landslide dumped 1,500 to 1,700 cubic yards of rock onto the eastbound and westbound lanes of the interstate, Andrew said. To put that into perspective, the landslide sent debris equivalent to 170 dump truck loads down the cliff face, onto the slope just above the highway and onto the four lanes. No one was injured.CDOT officials estimate the interstate suffered $1 million in damage.The largest boulder Andrew saw was 20 feet by 20 feet. He said material slid from a cliff face about 1,300 feet above the interstate. The chunk that broke off was about as big as a typical ranch-style house, he said.The crashing chunks of rocks sheared off 10 to 15 large-diameter spruce trees, Andrew said.

One lane in each direction was opened by about 3:15 p.m. Friday, after CDOT crews hauled material away and blasted additional rocks from a slope above the road. Once the threat of further sliding was reduced and the integrity of land bridges was tested, the interstate was reopened.The plummeting boulders punched holes on the inside and outside of the lanes on the land bridges but spared the middle, Andrew said. That’s why the lanes could be opened so soon, he said.The work was just a Band-Aid for the busy interstate.”We’ll be looking at weeks, if not a month, of work,” said CDOT spokeswoman Stacey Stegman. “We’re looking at probably $1 million in damage.”Andrew said even though this landslide was an unusual event, smaller slides are common and will continue in Glenwood Canyon. They are simply a product of snow or rain loosening rocks or freeze-and-thaw cycles sending material downslope.

The slides sometimes have tragic consequences. Art Daily of Aspen was headed west through the canyon in February 1995 when a large boulder fell onto the interstate and sheared off the right side of his Chevy Suburban. His wife, Kathleen Krieger Daily, and the couple’s two sons, Tanner and Shea, were killed. Art Daily was not seriously injured.Scott Condon’s e-mail address is scondon@aspentimes.com