More rockfalls and slides expected this summer due to weather

Jun. 30—In the wake of a Colo. 7 rockslide in June, officials said heavy snow last winter and rain this spring raised the risk for more slides this summer.

A wet winter and spring can cause rocks to loosen as water trickles under rocks into crevices and then freezes and expands, causing the rock to move, according to CDOT spokesperson Jared Fiel.

Boulder County underwent significant snowfall last winter, and is well above average rainfall this month after also receiving more rain the normal in May as well.

Boulder County Public Works Communication Manager Andrew Barth said rain is the main contributor to rockslides and the department is on higher alert during monsoon season in July and August.

"Rain just pulls that sand and gravel and that's when you're going to have your bigger slides," Barth said.

Fiel says crews from Region 4 of CDOT, which includes Boulder, frequently look out for signs of potential rock slides while out on the road doing maintenance.

"We expect above average rockfall activity to continue into the summer but the large slides like what happened on Colo. 7 are difficult to predict," Fiel wrote in an email. "Regarding precautionary measures, we're working with maintenance to track and inspect areas where they're seeing more frequent rockfall activity and following up with additional rock scaling work as needed on a site-by-site basis."

Along with putting up netting to catch fallen rocks, Fiel says roads are lined with catch basins where there is potential for falling rocks. These catch basins are ditches that line the road creating space between the road and the mountain side.

Fiel says the biggest indicator for a future rockslide is "smaller" rocks falling into the street.

"On some of our mountain passes it's kind of like a natural Jenga puzzle," Fiel says. "If one piece gets knocked out it could bring down the whole thing."

When crews come across an area that requires rock removal to avoid a rockslide, they first close the road and then use pry bars to loosen the rock, according to Fiel. If the rocks are too large they blast them into smaller boulders or rocks.

The Colo. 7 rockslide, which occurred between Allenspark and Lyons, was the fifth major rockslide in Colorado this year and took 11 days for CDOT crews to clear due to boulders the size of "fire trucks" and "garbage trucks" needing to be blasted into smaller sizes before being hauled away. Once they removed the fallen rock they uncovered a fracture that could have led to a future slide.

"We try to stay on top of it as much as possible," Fiel said. "Things were happening below the surface."

With residents living nearby, crews were unable to blast the rocks straight off the mountain. In these situations, Fiel said crews use materials like airbags to create space between the rock and the mountain — causing it to become loose.

While Fiel does not yet know where the Colo. 7 rocks will end up. Most boulders that are recovered by CDOT are used by the forest service to replace rocks that previously played a part in the ecosystem.

Fiel explained rocks that were previously moved by floods are replaced so fish can once again lay eggs or nest in the crevices of rocks underwater.

He also said sometimes the rocks are crushed down and used to pave roads. Previously boulders blasted from the Flood Recovery Project were used as the road base for Interstate 25.

Fiel encourages anyone who spots signs for a future rockslide to report it on the CDOT app. Barth said any information regarding emergency road closures in the county can be found at bouldercounty.gov/roads or @BoCoDOT on Twitter.