December saw a 13-year-high for potentially deadly natural avalanches — and an all-time record for human-caused ones — across Colorado. Here’s why.
Active snowfall following dry conditions has increased Colorado’s avalanche risks
Anne Gasper and her team traversed the mountainside of Vail Pass and headed into the heart of avalanche territory on a recent January afternoon.
Gasper, the lead snow ranger for the Vail Pass Winter Recreation Area, was rushing to post as much signage as she could about avalanche conditions — and speaking with anyone recreating in the area.
Recently, Gaspar’s field team has been working every day of the week, making for a typical season that will see a few thousand signs dotted across areas of Vail Pass, which straddles Summit and Eagle counties. Avalanche risks have increased in the area and beyond, with a record-level number of early-season reports.
Between Dec. 3 and Dec. 9, there were 243 natural avalanches considered large enough to kill or bury a person — the highest number for that week in the past 13 years, said Brian Lazar, deputy director for the Colorado Avalanche Information Center. During that same amount of time, there were also 27 human-caused avalanches of that size, the most on record for this early in the avalanche season, Lazar said.
Trends are similar in the Summit County region, which saw 170 avalanches between Oct. 1 and Jan. 2, according to Lazar. For that same time last year, the number was 138.
“We had a spike in avalanche activity early in December, and that’s unusual,” Lazar said.
Summit County has seen one death this season: Nick Feinstein, the son of University of Northern Colorado president Andy Feinstein. He was killed Dec. 31 when an avalanche engulfed him and his father while the pair were skiing in a backcountry area outside of Breckenridge Ski Resort.
Snowpack condition and avalanche frequency
According to Lazar, the reason for such an active early season has to do with the makeup of snowpack — and the timing between snowstorms.
Following a long dry spell, snowpack began to build much faster than usual in late November and into early December thanks to consistent winter storms. While snowpack accumulation is good for numerous environmental and recreational factors — from opening ski terrain to ensuring water supply in reservoirs come summer — it can also create the perfect condition for an avalanche.
“Snow is constantly changing. It’s never stagnant,” Lazar said. “Like with building any structure, you don’t want your weaker materials on the bottom.”
Such weaker materials include what some experts have colloquially dubbed “sugar snow,” which is grainier and loose-packed. As Lazar put it, it’s too weak to even form a snowball.
This snow tends to form during drier months and while it’s no threat on its own, it can be the catalyst for destruction once it’s buried by stronger, heavier snowfall.
This, Lazar said, creates what is known as a weak layer underneath the snowpack. Weak layers are larger and more angular compared to the smaller, rounder conditions of strong layers. When these strong layers form on top, its added weight can become too much for the weak layer underneath.
When these layers collapse, it releases the heavy snowpack on top, forming an avalanche. The threat to places and people differs, according to Lazar. Some travel mere feet and cause little to no damage. Others rip entire snowpack and underlying rock, transforming the face of mountainsides and leaving behind a football stadium’s worth of snow below.
“They come in lots of different sizes and shapes — some are wet and some are dry,” Lazar said. “The most dangerous avalanches — and the ones we’ve seen the most this past week in Summit County — are slab avalanches.”
These avalanches contain much stronger and cohesive snow and carry far larger volumes of snow compared to loose-snow avalanches.
In cases of natural slab avalanches, the amount of water held in the snow — know as the snow water equivalent — can create enough weight to push a weak layer past its breaking point. A recent system over the New Year’s Eve weekend brought a high snow-water equivalent storm to much of Colorado, Lazar said, which greatly increased the risk of avalanches.
Human-caused avalanches are also triggered by added weight as people traverse across weak snow layers.
Lazar said these avalanches tend to be triggered in shallower areas such as around rocks, cliff features or sparse trees because the weak layer is close enough to the surface to be affected by the weight of travelers.
Most of the avalanches reported so far this season have been large enough to bury or kill a person, Lazar said. These avalanches can weigh about 100 tons and travel 100 meters — roughly the length of a football field — and deliver enough snow to fill an average apartment room with 6 feet of snow.
Some avalanches are far smaller, weighing less than 10 tons and traveling just 30 feet — the length of a bus, according to Lazar. Others can be far larger, weighing about 1,000 tons, traveling 1,000 meters and bringing enough snow to cover an ice hockey rink in 6-9 feet of snow.
Lazar said there have been about a dozen avalanches of that size since late November. But while avalanches this large remain rare, Lazar said it can take as little as a foot to kill someone if it buries critical areas such as a person’s head.
“Even if your feet are sticking out of the snow, you could perish,” Lazar said, adding that as the amount of snow increases over a person, the longer it takes to dig them out. That means less time to breathe.
Being prepared in the backcountry
Skiers and snowboarders in mountain resorts typically don’t have to worry about being caught in avalanche territory, Lazar said, because of the dedicated resources those resorts have to mitigate and prevent such disasters.
“They can get the risk of avalanches pretty close to zero within a ski boundary,” Lazar said. The same cannot be sait for backcountry, where “no one is doing that mitigation work and so the chances of triggering an avalanche are much, much greater.”
Out-of-bounds recreation is becoming more common in the Summit region and with it comes the likelihood of avalanches, said Dillon District Ranger Adam Bianchi.
“A lot of people are new to backcountry travel, so we’re trying to educate about some of the risks associated with that backcountry use,” Bianchi said. “With more people out there, we’re going to see more of these occurrences happen.”
Bianchi said his district has seen a handful of human-caused avalanches recently, some of which have “trapped people and led to some close calls.”
Being prepared, and knowing about conditions, can be essential to avoid triggering a deadly event, Bianchi said. Equipment to carry includes a transceiver — which can send and receive wireless messages — as well as a shovel to dig through snow. Bianchi also said those recreating in avalanche-prone areas should never travel alone.
In the case of witnessing an avalanche, Bianchi said making a report to the avalanche information center and calling the Summit County Sheriff’s Office is critical to ensuring search and rescue teams know where they need to be.
The information center posts daily updates, as well as next-day forecasts, about avalanche conditions in Summit County and across the state at Avalanche.State.co.us.
Lazar said most avalanche deaths occur in mid-danger levels since lower-danger levels usually don’t see avalanches happen frequently and high-danger levels dissuade people from accessing terrain. Deadly avalanches are also mostly triggered on mountainsides at 30 to 45 degrees. In terrain terms, that translates to the average blue, black and double-black run.
Lazar said safe backcountry recreation should include taking avalanche safety courses and knowing how to use tools like a clinometer, which measures the angle of a slope.
The information center uses five categories to define avalanche risks for different areas of the state based on the potential size and frequency of avalanches. Those categories are: Level 1, low; Level 2, moderate; Level 3, considerable; Level 4, high; and Level 5, extreme.
Over the last week, Summit County and the surrounding region have been placed in either a Level 4 or Level 3 danger zone for avalanches, according to the avalanche information center, which also put an avalanche warning in effect for the Flat Top Mountains, Park Range, and Gore Range, which was in effect between Jan. 1 and Jan. 2.
As snowpack continues to build, Bianchi said it will be hard to know how avalanche conditions will change throughout the season.
“With the consistent weather we’ve been getting, it’s really challenging for that snowpack to settle up,” he said.
And even as risks persist, he said backcountry recreation is still possible. But staying informed and equipped is crucial.
“It’s not about staying out of the backcountry. It’s just about being prepared and knowing about what you’re doing before you go,” he said.
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