On a recent day along a snowshoe trail on Mount Rose, just outside Reno, Nevada, Wendy Antibus with the Sierra Avalanche Center checked the daily conditions.
“Today, our avalanche hazard is low,” she said, noting cooler temperatures and wind had helped freeze the snow’s surface.
But even on a low-risk day, she said, the snowpack can be more complicated than it appears.
“There can be cues in the snowpack, like sounds that the snowpack makes — like a ‘wompfing’ sound, cracking of the snowpack under your skis,” Antibus said.
Those subtle warning signs can point to instability beneath the surface.
In February, on a nearby mountain, avalanche danger was rated high. A guided group of 15 skiers was caught in a slide near Lake Tahoe, and nine people were killed, including six mothers who were close friends.
Human decisions play a major role
Understanding avalanches isn’t just about the snow.
Sara Boilen, a psychologist and backcountry skier, said human behavior is often a key factor.
“There are very few people who go out in the backcountry unaware of the fact that they're in avalanche terrain or at risk,” she said. “And we still take those risks, just like people ride motorcycles without helmets.”
Boilen said familiar terrain can create a false sense of confidence. After a fresh storm, when powder conditions are ideal, it can be easier to downplay danger.
Group dynamics can also influence decisions.
Research shows that as group sizes increase — especially beyond six people — avalanche risk can rise. Larger groups can create a false sense of security, while subtle social pressure can push people to take bigger risks.
“We don't have human-related or human-caused avalanches without humans,” Boilen said. “All of the decisions, it’s all being filtered through very, very human eyes and brains.”
And those decisions aren’t always obvious in the moment.
“It is incredibly difficult to notice all of the decisions that are leading you towards an avalanche incident,” she said. “Whereas in hindsight, it's incredibly easy to see all of them.”
Changing winters, more complex snow
Scientists say environmental conditions are also shifting in ways that can increase risk.
Erich Peitzsch, a researcher with the U.S. Geological Survey’s Northern Rocky Mountain Science Center, studies snowpack and avalanches in the Mountain West.
He says avalanches require a few key ingredients: a steep slope, a weak layer in the snow, a slab of snow on top — and a trigger.
Those fundamentals haven’t changed. But weather patterns are changing.
“We have a storm, and then it's sort of dry for a while, we develop those weak layers, and then we get another storm and put it on top,” Peitzsch said.
That stop-and-start pattern can create what scientists call “persistent weak layers,” buried weaknesses in the snowpack that can linger for long periods.
In other words, a quiet stretch of weather can set the stage for danger, long before the next storm arrives.
Researchers say these kinds of variable winters are becoming more common in parts of the Mountain West, creating snowpacks that are harder to predict and easier to trigger. Investigators are examining those conditions in the Lake Tahoe avalanche.
What it means for the future
Back on Mount Rose, Antibus said these shifting conditions are making avalanche forecasting more challenging.
“It makes it harder for forecasters to anticipate conditions as we see different scenarios in the climate,” she said. “As we have warming and more rain, we might have more avalanches involving wet snow.”
Wet snow avalanches are less understood than dry ones, but research suggests they may be happening earlier in the season as temperatures warm.
And conditions can change quickly.
Since that day on Mount Rose, avalanche danger in the area has already risen from low to moderate.
This story was produced by the Mountain West News Bureau, a collaboration between KUNR, Wyoming Public Media, Nevada Public Radio, Boise State Public Radio in Idaho, KUNC in Northern Colorado, KANW in New Mexico, Colorado Public Radio, KJZZ in Arizona and NPR, with additional support from affiliate newsrooms across the region. Funding for the Mountain West News Bureau is provided in part by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
