Avalanche danger in the Utah mountains has been high this year. Over 50 avalanches have been recorded across the state in the last week alone, according to the Utah Avalanche Center.
Craig Olsen, avalanche supervisor with the Intermountain Division of the National Ski Patrol, said that the weather this winter has created unstable layers of snow in many areas.
"This year is very dangerous because we had an early snowpack which left … some rotten layers at the bottom. And then we hurry and packed a whole bunch of new snow on top of it. So it hasn't had time to settle out," Olsen said.
Nathalie Vriend is an associate professor of mechanical engineering at the University of Colorado, Boulder. She studies granular flow, or the physics of phenomena like sand dunes, landslides and avalanches. She said a cross-section of the snowpack on a slope can be read like tree rings to understand the history of a snow season.
“The cross-section features different types of snow. And some of them bind really well and consolidate really well. And other parts of a slope may actually be very unconsolidated," Vriend said.
When fresh snow falls on an unconsolidated layer, Vriend said, the weight of the snowpack creates conditions that are prime for what are known as slab avalanches.
“And this entire slab can start to flow on top of this weak layer, because a part of the mountain breaks away," Vriend said.
Both Vriend and Olsen say slopes between 25 and 45 degrees are the most dangerous for avalanches.
“If the slope is lower than 25 degrees, typically the slope is not steep enough … for the snow to pick up speed,” Vriend said.
“Usually, the bigger avalanches occur between 35 degree slopes and 45 degree slopes. Above 45, they tend to slide on their own and usually aren't as big a deal," Olsen said.
So what angles are the slopes that skiers enjoy?
“Well, if you talk with my kids, the steeper the better," Vriend said. "Obviously, when the slope is too shallow, you can't really brake because otherwise you're standing still. I think a typical really steep slope that you would encounter is something like 40 degrees. And that is a Black Diamond slope."
Avalanches can occur whenever the conditions are right, Vriend said. During fieldwork in Switzerland, she measured the speed of an avalanche using a radar gun. The snow reached speeds of up to 50 meters per second or 111 miles per hour. Even if you managed to stay on your skis, Vriend said you cannot outpace a serious avalanche.
At resorts, ski patrollers constantly monitor conditions and use mitigation tactics to prevent dangerous avalanches. For backcountry recreation, Olsen said, it is important to check the avalanche forecasts. If you choose to recreate in the backcountry, bring a transceiver, an avalanche probe, and a shovel.
“Having that gear doesn’t necessarily make you safe. Also, have people with you that have the same skill set, and, and the will and the ability to dig you out if you're the one that's caught, because you're only going to have at best — if you're not killed from the … tumultuous ride and through all of the debris and trees — if you survive all of that, you're only going to have about a 50/50 chance of survival after 15 minutes of just suffocation. And that's not very good,” Olsen said.
“So usually, if you look at avalanche calamity reports, people that are rescued are usually rescued by their peers. And if they're waiting for mountain rescue, that usually takes hours. By then, unfortunately, if somebody is trapped, they perished," Vriend said.
More important than gear and preparation, Olsen said, is having the ability to say no. The lure of a fresh track can lead people to make risky decisions.
“And that's that is the most important word in all of avalanche, I think, is being able to say, not today, or not this run … it's just snow. you can wait," Olsen said.
For more information about avalanche conditions in Utah, visit utahavalanchecenter.org.
