Explosive Charges Protect Backcountry Skiers

As the coronavirus pandemic rages on, many winter sports enthusiasts are skipping their usual ski resort visits in order to avoid contagious crowds or preemptive shutdowns. But that does not mean they are giving up on skiing, snowboarding and snowmobiling. Many are instead venturing into unpatrolled and ungroomed backcountry terrain. Specialized backcountry equipment retailers and manufacturers are, in fact, reporting record sales. And some skiers are skipping backcountry safety lessons before heading off-piste, with potentially deadly results: the week before Christmas, at least three Colorado backcountry skiers died in avalanches, and a fourth perished on December 26.

Avalanches have, of course, been part of the winter landscape for as long as snow has fallen on mountains. During the 2018–2019 winter sports season, the Colorado Avalanche Information Center documented thousands of these events, which hit 135 people and killed eight, in that state alone. Now increasing traffic in the backcountry is not only exposing more people to risk but is actually making avalanches more frequent, says Paige Pagnucco, an avalanche education and outreach specialist at the Utah Avalanche Center. “We have had an increase in human-triggered avalanches because we have more people in the backcountry accessing that terrain that’s questionable,” she explains. Under the weight of even a single skier, an unstable snowfield can shift and send loose snow thundering down a mountainside.

In attempts to prevent avalanches from sweeping skiers off the runs and pushing cars off the roads, officials tasked with protecting winter sports terrain and state highways must clear steep slopes of deep, unstable snowpack. They usually do so by setting off explosions that send snow cascading down mountains in planned slides. In 2018–2019 the Colorado Department of Transportation conducted more than 1,400 detonations, causing almost 900 avalanches. Many of these blasts are still produced with traditional methods. New cutting-edge technologies are quickly becoming more common, however.

AN EXPLOSIVE HISTORY

In the U.S., humans have been unleashing ordnance against avalanches since just after World War II. Monty Atwater, a veteran of the U.S. Army’s 10th Mountain Division, spent part of the war in Europe, where he saw military artillery used to trigger snowslides and clear slopes. He brought the idea to Utah in 1946, when the U.S. Forest Service (which regulates ski resorts on public land) hired him to serve as “snow ranger” at the state’s Alta Ski Area. Alta became the first American ski resort where artillery was used to clear snow from steep mountain passes.

Avalanche fighters still use military weapons today: About 40 surplus 105-millimeter howitzers leased from the U.S. Army are currently deployed by nine ski resorts and seven state transportation departments. The weapons can throw an 18-kilogram explosive projectile up to 11 kilometers. Trained ski patrollers and staff from state transportation departments aim the howitzers at steep, high-mountain terrain with historical records of avalanches. When the rounds strike their target, they explode and trigger snowslides that can sometimes be massive. The Avalanche Artillery Users of North America Committee, a nonprofit organization, manages the artillery-avalanche-control processes across all 16 existing U.S. programs.

“There’s nothing more cost-effective than an artillery system for avalanche mitigation,” says Jamie Yount, a certified master gunner and president of the Avalanche Artillery Users of North America Committee. Yount is also the winter operations program manager for the Colorado Department of Transportation, where he monitors approximately 300 avalanche paths that could threaten ski resorts or transportation corridors.

REMOTE CONTROL

Artillery is a proved and effective way to help control avalanches. But unfortunately, most howitzers are almost 60 years old. With limited access to maintenance expertise and spare parts to repair these aging tools, avalanche managers are moving to new technologies.

Some of the latest mitigation mechanisms, called remote avalanche control systems (RACS), are being permanently installed along paths that are at high risk of being buried by avalanches. RACS can trigger avalanches at any time and in any weather via signals sent over a cellular network (or through backup radio control if that network fails). Those signals tell the installation to deploy a specific type of explosive charge, depending on the system.

One such system was developed by a Switzerland-based company called Wyssen Avalanche Control. The Wyssen avalanche tower, which varies in height, depending on its location, has explosive charges stored in a box at the top. When the tower receives secure commands through a cellular system, a panel on the box opens and drops a charge, which is attached to a cable that lowers it to a preset height above the snowpack. Igniters are activated as the charge falls. And after a time delay, they set off the explosion.

“Remote control systems like the Wyssen tower are more efficient and much safer [than artillery or handheld explosives] because you’re removing the charges from the hands of people,” says Roz Reynolds, U.S. representative of Wyssen Avalanche Control. The technology lets humans control avalanches without physically entering a potentially dangerous snowfield. On the other hand, permanent systems such as this one are more expensive to install—and because explosive charges are stored on-site, companies can face legal scrutiny.

Despite these challenges, Wyssen says it has installed almost 600 mitigation towers worldwide, including more than a dozen in the U.S. The Utah Department of Transportation placed the first of these in Cardiff Bowl, across the highway from the Alta Ski Area, in 2017. Since then, state transportation departments have put up a total of 13 Wyssen towers in Utah and five in Colorado.

Bomblike explosive charges are not the only option for remote avalanche control. Two RACS, called Gazex and O’Bellx, ignite a mix of propane and oxygen to create a concussive force on demand. The Gazex system consists of a network of pipes and a small structure that houses oxygen and propane tanks permanently installed in known avalanche start zones. Remotely controlled valves release the gases into the pipes. When they build up to a certain point, a firing mechanism ignites them, creating a downward-facing pressure wave that punches into the unstable snowpack to trigger an avalanche. The O’Bellx system uses a similar gas-based method but looks different than Gazex. O’Bellx units resemble rocket nose cones, and they sit on towers built on high-risk avalanche slopes.

These systems share many of the Wyssen towers’ advantages, with remote control making them available 24/7 in all weather conditions. The technology they rely on makes them safe for operational staff and the public because the explosive gas mix is created only when needed, says David Poulet, a safety marketing manager at the French winter sports company MND, which manufactures both the Gazex and O’Bellx systems. “There’s no risk of duds or sliding charges in avalanche areas,” he says.

MND says it has sold these systems to American ski resorts—including Alta, Brighton Resort in Utah, Jackson Hole Mountain Resort in Wyoming, Squaw Valley Ski Resort in California and Taos Ski Valley in New Mexico—and has set up almost 200 units throughout the U.S. Despite higher initial installation costs, compared with artillery, Poulet says demand for remotely controlled avalanche systems is increasing. “There’s a necessity to keep highways closed for the shortest possible time, as well as ski resorts opened for as long as possible,” he notes. And with more people ditching groomed ski trails for backcountry, avalanche-prevention experts will need all the tools at their disposal to wipe snow off potentially dangerous areas.