A loud bang reverberates in the Dolores Valley north of Rico, and a white plume erupts from a steep gully high above Colorado Highway 145.
In seconds, a wave of snow hits the closed highway, then settles into a pile more than 6 feet deep.
A front-end loader appears and clears a highway lane in 15 minutes, and the road is open again after being closed for about 35 minutes.
It was just a morning’s work.
The avalanche mitigation was conducted Feb. 17 by the Colorado Department of Transportation using a new remote control system installed in the fall.
Five 30-foot-tall towers that lower explosive charges on a tether were installed in “frequent offender” slide paths that lurk above the state highway between Rico and Lizard Head Pass.
The systems were provided and installed by Wyssen Avalanche Control of Switzerland. They are safer and more efficient way to mitigate avalanche danger for travelers, said CDOT maintenance supervisor Todd Jones.
“This system is a more versatile tool for controlling these slide paths that run pretty often,” he said.
During an active winter, the Yellow Springs, Yellow Wall and Peterson slide paths, where towers were placed, can produce natural avalanches many times a week, or even per day. They might or might not hit the highway.
“Our main goal is to bring down smaller avalanches frequently to avoid a large natural one,” Jones said.
The remote control system reduces traffic delays, he said, and can be used at night or in low visibility during storms.
The explosives do not have to be handled, and the control work can be done with fewer staff members in harm’s way.
Project cost $1.4 millionThe more common CDOT avalanche control methods use the Avalauncher nitrogen cannon or a howitzer that shoots an explosive charge into the path from the road. Sometimes, helicopters are used to drop a charge. They all require good daytime visibility, and crews tend to be closer to the hazardous slide path. CDOT uses the Avalauncher on Highway 145, and from helicopters on other slide paths around Lizard Head Pass
The highway towers were activated last week. The project cost $1.4 million and was deployed to mitigate the troublesome Yellow Springs, Yellow Wall and Peterson slide paths.
Four of the five towers released charges and triggered slides. One slide reached the highway from the Yellow Springs gully, and one failed to drop and did not detonate. The tower was being reviewed by Wyssen and CDOT technicians, who were monitoring the mission with a live data feed.
CDOT partners with the Colorado Avalanche Information Center to analyze and conduct avalanche control work on roads.
Becca Hodgetts, CAIC forecaster for the mountains of southern Colorado, was at the scene to analyze avalanche conditions along the highway and review the triggered slides.
She said a dry start to the winter led to weak layers at the base of the snowpack, increasing the potential for avalanches.
“It has been a pretty dangerous year, and it’s somewhat anomalous,” Hodgetts said. “On the way up here, I could see signs of fresh avalanches.”
Extreme avalanche conditions seen this winter happen about once every 10 years, she said.
The Colorado Department of Transportation has partnered with CAIC on highway avalanche control work since 1991, said CDOT spokeswoman Lisa Schwantes, and there has not been a CDOT highway avalanche death in that time. A CDOT worker was killed by an avalanche on Red Mountain Pass in 1990.
An efficient systemBefore the towers dropped the explosives into the slide path last week, the highway was closed in both directions, and a sweep ensured the area was clear of vehicles and recreationists.
CDOT crew members wore avalanche beacons and observed the avalanche from a distance. During the early morning work, temperatures were below zero.
Spotters were positioned to watch for secondary avalanches that could be let loose from the concussive blasts. Traffic control crews blocked traffic in both directions a safe distance away.
When the highway was closed and crews were in position, Jones sent a coded command from his cellphone that told the tower to lower and release a charge above the slide path. The tower’s deployment box then reset, ready to deploy another charge.
The CDOT crew and CAIC were impressed by the results.
“The system is efficient and improves safety for CDOT crews and the public,” Schwantes said.
“It’s good. We’ll take it. You can see it released the recent fresh snowfall,” Hodgetts said, and it reduced the risk for a natural slide onto the highway.
The new technology is favored by CDOT because of its efficiency and reliability. Traditional howitzers likely will be phased out of avalanche control because of their age, Schwantes said.
CDOT operates more than 30 remote control avalanche systems at several locations on high mountain highways and the Interstate 70 corridor. In Southwest Colorado, they are used on Highway 145 near Lizard Head Pass, on U.S. Highway 160 at Wolf Creek Pass and on U.S. Highway 50 at Monarch Pass.
Every winter, CDOT and CAIC monitor and control about 278 of 522 known avalanche paths above Colorado highways.