Remote-controlled avalanche mitigation in Colorado began in 2015 on Stanley Mountain above U.S. 40 on Berthoud Pass. The idea was that frequently triggered, remote-controlled explosions from the five Gazex exploders in the Stanley slide paths would prevent a large accumulation of snow and reduce the risk of unexpected, large avalanches burying the highway.
“But when you talk with the old guard avalanche workers, this theory has not been proven. There is still kind of an open question about whether this kind of (remote controlled avalanche) mitigation changes the return period of large avalanches,” said Ethan Greene, the executive director of the Colorado Avalanche Information Center. “Looking at the return rates of road hits on Stanley, and the rate has not changed much since the 1970s.”
When conditions align to produce large, destructive avalanches — a rare confluence of major snowstorms and high wind loading a weak, persistent layer buried in the snowpack — not even remote-controlled avalanche control systems work perfectly.
This winter CAIC and the Colorado Department of Transportation closed U.S. 40 on Berthoud Pass five times for avalanche mitigation, including a skier-throttling 78-hour total road closure over the MLK holiday weekend.
On Feb. 28, the Gazex exploders on Stanley created a very rare D3 avalanche that buried U.S. 40, forcing a closure for more than three-and-a-half hours. (D3 is defined as a “very large avalanche” that can bury and destroy a car, damage a truck and destroy a small building.) The slide was an example of the widespread persistent slide problem that CAIC is trumpeting to all backcountry travelers, warning of “valley-crushing” avalanches sliding on layers of faceted snow.
The storm over the MLK weekend qualified as a “major snowfall event,” according to CAIC, which means it ranks in the 99th percentile of 7-day snowfall ever measured atop Berthoud Pass. The slides that closed U.S. 40 for three days over the MLK holiday — including a Jan. 14 slide that buried 10 cars — were on the west side and involved 1.5 miles of road banks that are less than 50-feet tall.
The Feb. 28 slide — the first D3 from a remote-controlled avalanche system since the historic avalanche cycle in March 2019 — was triggered by the largest exploder in the Stanley array, which ignites three cubic meters of propane and oxygen gases. That slide connected across multiple slide paths to bury U.S. 40 on the east side of Berthoud Pass for the first time this winter.
How remote avalanche control started
Remote avalanche control in Colorado began in 2015 with the five French-made Gazex exploders placed in zones atop the Stanley Mountain and 11 installed in the Seven Sisters paths above U.S. 6 on the east side of Loveland Pass. The first remote avalanche control systems in Colorado — they call them RACS — were part of a plan to phase out the use of 105mm artillery fired from World War II-era Howitzers. (In 2014, two CDOT explosive experts were injured when an avalanche mitigation mortar exploded inside the barrel of an Avalauncher, which uses compressed gas to propel explosives that detonate on impact.)
In 2018, CDOT installed O’Bellx exploders on the other side of Berthoud Pass and at three locations near the Eisenhower-Johnson Memorial Tunnels above Interstate 70. The O’Bellx pods, which are removed in the spring and reinstalled with fresh gas every winter, use a smaller volume of hydrogen and oxygen than the Gazex exploders. A year later CDOT installed three Gazex exploders on Monarch Pass above U.S. 50.
In 2020, CDOT installed five Wyssen Avalanche Control towers above Colorado 145 on Lizard Head Pass. The remotely controlled Swiss system dangles explosives on cables just above the snowpack in slide paths.
CDOT last year installed two Gazex exploders and three O’Bellx systems in starting zones of three slide paths above U.S. 550 on Red Mountain Pass.
Today, there are 54 RACs above Colorado roads on Berthoud, Lizard Head, Loveland, Monarch and Red Mountain passes. CDOT has plans to expand the program with hopes of eliminating the use of seven Howitzer cannons in four areas by 2030.
Since 2015, CAIC has tracked hundreds of avalanches triggered by RACs and all but a handful rank higher than a D2, which is defined as an avalanche that can bury people.
Since CDOT and CAIC began tracking slides in the Stanley path, the agencies have seen avalanche debris reaching the road about once every 1.6 years. Since CDOT installed the Gazex exploders in the Stanley Path, that length of time between road burials has not changed.
Greene and his teams compiled the Berthoud Pass avalanche activity for this winter in a report that concluded the total road closure time during mitigation work has decreased with the RACs but “we will still have longer closures when large amounts of debris reach the road.”
Greene said the remote avalanche control system works well in Colorado. But it is not designed to work perfectly when conditions create avalanche conditions that are 20-year events.
Could more exploders help?
“A lot comes down to how much do you want to spend and how much do you not want to have access to the slope,” Greene said. “I think the program is actually working pretty well. That’s not to say we could do other things but there is a cost in actual dollars plus closure times for the highway.”