Eagle County, surrounding area now in rockfall season
No slides have hit the valley yet, but rocks tend to fall as winter turns to spring
As winter gradually turns to spring, an in-between season hits the high country: rockfall season.
As daytime temperatures rise, snow melts. Water trickles into cracks in rocks on hillsides, then freezes, expands, and can loosen rocks. Snowmelt can also erode soil under other rocks, causing them to slide.
The first big rockfall of the season hit March 8 near Steamboat Springs. There, erosion contributed to a rockslide that closed U.S. Highway 40 for several hours.
Identifying trouble spots
Like most of Colorado’s seasons, it’s hard to tell just much rockfall the area might experience. Ty Ortiz, manager of the Colorado Department of Transportation’s geohazard team, said the cool, wet spring of 2019 resulted in a longer-than-average rockfall season.
Ortiz said his interest in rockfall and geology was spurred in the early 1990s by rockfall work in Glenwood Canyon, home to roughly 30 rockfall fences along the north side of the canyon.
Dating to the time when rail lines first ran through the mountains, there was often more observation than hard data in working to ease the effects of the annual rockfall season.
Back when Interstate 70 through Glenwood Canyon was being built, Ortiz said the Colorado School of Mines had only recently developed a program to identify rockfall zones and try to ease the damage from those incidents.
Modeling software has become better over the years, and Ortiz said data now plays a large role in mitigating damage from rockfall.
Rocks still hit roads
Damage can be significant. A slide several years ago originated 800 feet up the canyon’s north wall, releasing about 1,500 cubic yards of material. A cubic yard will roughly fill the bed of a standard half-ton pickup.
Gravity, combined with the weight of the rocks, can create some very large impact forces.
Ortiz said the most sturdy rockfall fence used today can absorb energy equivalent to a loaded tractor-trailer rig running down the road between 60 and 70 mph. A big rock from a significant height can create forces far greater than that, Ortiz said.
Some rockfall containment systems are designed to slow down rocks to keep them from falling into the road. A stretch of U.S. Highway 24 on Battle Mountain has one of those systems, as does a stretch of I-70 just west of Georgetown.
With all that work, rocks still hit roads.
Projects on tap
Ortiz said transportation officials are now working on ways to ease rockfall danger on longer stretches of road.
“We were mitigating 400 or 500 feet of a corridor, but that corridor might be 5 miles long,” Ortiz said.
The idea now is to do work on those longer stretches as the budget allows. This year’s projects are on State Highway 133 on McClure Pass and on Bear Creek Canyon near Evergreen. Crews will spend much of their time this year in those corridors.
This summer will also see some rockfall mitigation work in Glenwood Canyon during an eight-month construction project on the westbound lanes.
Ortiz said work will include an update to the last of the old rockfall fences in the canyon.
Even with good planning, dealing with rockfalls involves a lot of after-the-fact work. Ortiz said two team members are dedicated to responding to rockfalls around the state. That includes some technical climbing up to areas that have moved.
That work can be tricky and dangerous, Ortiz said, especially in areas like Battle Mountain.
While the work continues, it’s unlikely our roads will ever be 100% protected from rockfall. It’s best to look out, and be prepared for detours.
Vail Daily Business Editor Scott Miller can be reached at firstname.lastname@example.org or 970-748-2930.
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