Adventurous scramblers who peek into a steep avalanche gully in the Hoback Canyon might think they’ve been transported to Naboo, home-world of Star Wars droid R2-D2.
Gazing into the Cow of the Woods slide path, an adventurer would spy a robot eerily similar to, but much larger than, the fictional movie character. The real-life Hoback Canyon robot doesn’t contain the schematics to the Death Star battle station or a distress call from Princess Leia, but it is a life-saving droid nevertheless.
The sole job of the Hoback droid is to spark a gas explosion to provoke snow avalanches when the Wyoming Department of Transportation wants them to slide. The state agency first closes U.S. Highway 191 between Bondurant and Hoback Junction. Workers then employ the remote, robotic exploder when no cars or people are in the danger zone below the avalanche chute.
WYDOT operates a handful of remotely operated avalanche exploders above two highways in Teton County. They create explosions after a mixture of gas and oxygen is ignited in a large tube or cone. The force is directed toward the snow and causes it to slide. In recent years they’ve reduced the avalanche threat to motorists and shortened the time highways are closed during winters.
But the first exploders WYDOT installed — on Mount Glory above Wyo 22 between Wilson and Victor, Idaho — have some limitations. A supply building nearby is stocked with gas and oxygen before winter begins. Because they are permanent, large, culvert-type devices, they have to be serviced where they were built. They require upkeep.
“They blow up,” said Jamie Yount, agency avalanche technician. “It’s a hard life. It all takes maintenance. You need to be up there,” and sometimes in winter.
A dangerous place in winter
Winter maintenance on Mount Glory — the destination of countless backcountry skiers — is one thing. But nobody skis near or around the steep, cliff-framed Cow of the Woods slide path in Hoback Canyon. Even though he’s pretty much the world authority on that particular chute, “I’ve never been to the starting zone in the wintertime,” Yount said.
Enter R2-D2, officially known as an O’Bellx exploder. It is an aluminum cone with gas storage and electronics. The O’Bellx can be hoisted by helicopter to an avalanche-resistant pedestal constructed in the summer in the slide starting zone. An airship picks up the O’Bellx on a tether, flies it to the pedestal, and deposits it there where it is secured automatically.
The O’Bellx contains a salvo of hydrogen and oxygen that can be spewed and ignited from a safe position on the highway. It was invented by TAS, a European company specializing in the control of natural hazards.
“If I need to bring it down and put more gas in it, I can just hire a helicopter,” Yount said. Maintenance can also be done at a site of WYDOT’s choosing, not up in the cliffs.
“For this terrain that’s really difficult to access, that’s the real advantage,” he said. “You can retrieve it by helicopter without having to go up there.”
WYDOT installed the first O’Bellx in North America — at Cow of the Woods — in the fall of 2013. It installed its second, also in Hoback Canyon, at the Calf of the Woods slide path in 2015.
Before the O’Bellx, WYDOT would bring down slides with artillery or by dropping hand charges from a helicopter. The artillery shot was a difficult one, however, requiring a high-angle trajectory into a hidden starting zone.
“It’s challenging to get the rounds in there,” Yount said. “We are going to phase out of artillery in one more year.”
WYDOT’s O’Bellxes each weigh about 1,400 pounds and are good for nine shots each before reloading. They can be serviced with the light-duty Teton County SAR airship. They could be configured for twice as many shots, but then reloading would require a larger helicopter.
“It’s a big bang,” Yount said of the O’Bellx blast. “I have full confidence we are affecting the snowpack. Those starting zones are quite small.”
By comparison, the four permanent Gazex exploders on Mount Glory use propane and oxygen. The first was installed in 1992. Gas is ferried to a supply hut and fed to the exploders through pipes buried underground. WYDOT has two other remotely operated devices on Mount Glory — North American Avalanche Guard systems that lob 9 pound charges onto the slopes. Highway workers can detonate about 90 explosions on Mount Glory without having to restock — enough for a normal winter.
The Gazex exploders cost on the order of $50,000 each. Installation would add another $100,000 to the cost of each if contracted out. WYDOT did that work itself.
A single O’Bellx costs approximately $145,000. WYDOT put up the Hoback array for about $325,000, Yount said. The payoff comes in the reduction of highway closures.
Using the department’s Howitzer, closure times in the Hoback Canyon averaged 77 minutes. With the O’Bellx, the average closure time is 26 minutes.
“We’ve gone down to the Hoback and done avalanche control in 7 minutes,” Yount said. “I think it’s a worthy investment.”
“It’s ingenious,” WYDOT commissioner Bruce McCormack said of the technology. Fellow commissioner Todd Seaton is similarly impressed. WYDOT no longer has to wait for nature to act first. “In an hour or two in the middle of the night, we’ll take care of it,” he said.
WYDOT has at least two other types of avalanche structures. One is a series of snow-supporting fences above U.S. Highway 191 just south of Jackson. The devices keep the snowpack in place when it would normally slide.
The other is an old-world solution that was built in the Hoback Canyon in 1971. The story begins with an epic winter in 1949 that built up a dangerous snowpack above the Hoback River.
On the south side of the river and Hoback Canyon a large, destructive avalanche cut loose, crossed the river and buried the highway, which was located on the north bank.
The slide path earned the name Bull of the Woods. The Cow of the Woods and Calf of the Woods were named later. “It left a big enough impression on WYDOT officials that when they realigned [U.S.Highway] 191 around 1970 … they decided to do some mitigation,” Yount said.
That preventative work involved mounding up 30-foot-high pyramids of earth and rocks. Similar mounds had proven effective in Europe. Yount was eventually able to document how well they work at the Bull of the Woods.
In 2014 a significant avalanche cycle hit the Jackson Hole area and destructive “Class 5” avalanches occurred around the valley. An avalanche in the Bull of Woods roared down the mountain. “The air blast alone probably destroyed 10 acres of trees,” Yount said. Debris trickled down to the river, but airborne snow crossed the Hoback and reached the highway beyond.
“The dust cloud put 4 to 5 inches of snow on the road,” Yount said. “The mounds saved the highway, no doubt in my mind.”