How do resorts try to prevent avalanches like the one that took three lives in Idaho this week? It’s complicated

Every morning in ski resorts across the world, patrollers do what they can to mitigate the inherent dangers of a mountain environment.

It’s no different for regional resorts.

That starts with paying close attention to the weather.

“We’re tracking the weather … before the mountain opens and tracking the snowpack over the course of the season,” said Tom Eddy, Schweitzer Mountain’s snow-safety supervisor.

In addition to the obvious things, like temperature and snowfall for instance, wind is also an important factor when making weather-related safety calculations. A so-called “wind slab” is formed when the wind blows snow onto leeward terrain. This can deposit snow “10 times more rapidly than snow falling from the sky” and can be highly unstable, according to Avalanche.org.

The constant monitoring aims to give patrollers a clear understanding of the snowpack, particularly the likelihood and whereabouts of a possible avalanche.

Once the resort opens, patrollers actively manage the snowpack. That means checking terrain and trying – in two main ways – to trigger avalanches.

For steeper, more avalanche-prone terrain, patrollers use explosives. At Schweitzer, patrollers use charges of dynamite that weigh 2.2 pounds. If they believe there is a deeply buried weak layer of snow, they may tape two charges together to get a bigger blast, Eddy said.

Even dynamite doesn’t always trigger an avalanche. In fact, in most cases it doesn’t.

“It’s a small percentage,” Eddy said of the effectiveness of dynamite in triggering a slide. Still, he said, “explosives are our best tool to really look at instabilities in the pack.”

After blasting an area, patrollers assess the results and then, depending on the outcome, they may toss another charge or “ski cut” it.

When ski cutting, a skier travels along the top of the slope, at the transition point between flatter terrain, where gravity still anchors the snow to the ground, to steeper terrain. This area is where most avalanches start. But ski cutting can be dangerous.

Schweitzer has five main “mitigation routes.” These are areas known to be prone to avalanches and to which patrollers pay special attention.

Finally, patrollers rely on skiers and snowboarders to compact the snow.

“Skier compaction is a great tool for mitigation,” Eddy said. “If it’s snowing hard during the course of the day and we don’t have the skier traffic to help compact, that’s when we close terrain.”

Exactly what happened – or didn’t happen – in the lead up to Tuesday’s avalanche at Silver Mountain isn’t yet known, although witnesses did say Wardner Peak was bombed by the ski patrol Tuesday morning. However, the peak had not been open prior to Tuesday, due to limited snowfall.

As for Silver Mountain’s patrol routine, it is similar to Schweitzer’s, according to a former Silver Mountain patroller.

Because Wardner Peak is steep and exposed to the wind, it is bombed regularly by patrollers.

Patrollers ski predetermined routes, starting at the top of the peak and working their way down. At each station, which is marked, patrollers toss a bomb. They then assess what happened and ski cut the slope before moving to the next station.