When an avalanche occurs, the whole mountain reverberates. The whirling mass approaches like a steam locomotive, picking up thousands of tonnes of material on its descent and hurling clouds of snow into the air at speeds of up to 130 kilometers (80 miles) per hour.
They are one of the most dangerous phenomena in the mountains. Nine skiers, including six close friends, were killed in an avalanche in California on Tuesday.
And this winter in Europe turned out to be especially deadly.
According to the European Avalanche Warning Service (EAWS), at least 99 people have died since October 2025, most of them in the Alps. The Alps serve as the continent’s ski capital, spanning multiple countries including France, Italy, Switzerland, and Austria.
According to EAWS, 28 people have been killed in avalanches in the French Alps alone since the winter’s first fatality occurred on December 26th. This is a significant increase compared to the average of eight deaths normally seen at this point in the season, according to the French National Association for Snow and Avalanche Research (ANENA). In Italy and Switzerland, avalanche deaths are also much higher than normal.
And in a demonstration of its terrifying power, an avalanche derailed a train in Switzerland on Monday, injuring five passengers, and earlier this month another avalanche crashed through a French mountainside shelter, smashing windows and dumping a snowdrift into the building’s kitchen.
An avalanche requires a combination of three things: snow, a steep slope greater than 30 degrees, fresh or melted snow, and a trigger: a person, animal, or wind.
Of course, these are present in the Alps every winter, but certain conditions make this winter more dangerous than others, explained ANENA director Stefan Borne.
According to him, after the first snow fell in November, a long period of high pressure continued, causing the snow on the ground to develop into “angular grains.” The grains resemble large sugar crystals and do not bond effectively with the surrounding layers.
This type of snow is not dangerous in itself. But when covered with fresh snow, “these vulnerable layers can be triggered and act like ball bearings, like a conveyor belt that allows avalanches to slide very easily,” Bornet said.
Several meters of fresh snow has fallen across Europe in recent weeks. This is part of a weather pattern caused by an unusual southerly jet stream, dumping large amounts of precipitation across the continent and causing flooding in low-lying areas.
At the same time, Bornet added, “the snowpack is being carried by the wind, which means there’s a lot of snow on the ground.”
The situation has prompted several regional avalanche forecasting services to issue severe level 4 warnings for much of the past two weeks, with some areas reaching the most severe level 5 warning for at least several days.
Still, these dangerous conditions are unusual but “not abnormal,” said Christine Pillmayr, an avalanche forecaster at the SLF Institute for Snow and Avalanche Research in Switzerland.
He told CNN that these symptoms can occur approximately every five to 15 years, stressing that this number is only a statistical guide, so hypothetically the symptoms could occur two winters in a row, or not at all for a longer period of time.
Scientists say it’s difficult to measure how the climate crisis will affect the frequency of these avalanches. Weather is ephemeral in nature, similar weather patterns can have different effects on the environment depending on existing conditions, and comprehensive datasets are not really available.
“It’s difficult to draw a direct relationship,” Bornet said. “We know the climate is evolving, we can’t deny that.”
One effect that is clearly attributable to climate change is the variation in the rain-snow line, which means “we have weather patterns that bring snow at very low altitudes, and the next day it can rain at 2,000 meters or 2,500 meters,” he said.
In some cases, this “strengthens the snowpack through sedimentation and consolidation,” making avalanches less likely, but “in some cases it can make the snowpack heavier,” he added.
Even though mountains may seem tamed by tourist infrastructure, they remain wild and dangerous, especially in situations like this.
For many, that represents the appeal of backcountry skiing. It’s your chance to test yourself against the terrain and roam freely on pristine snow, unrestricted by groomed runways.
Despite this temptation, most advanced skiers stick to marked slopes in dangerous situations. But some tourists, especially those who may have spent thousands of dollars on a week-long ski vacation, are less likely to heed avalanche warnings.
“If you invest time and money, you can’t get it back, so you want to get some return on that investment, and that pushes the limits,” Audun Hetland, who studies decision-making in avalanches at the Norwegian Arctic University, told CNN.
And while professional guides and skiers can spend days assessing difficult terrain, tourists are given none of that time, Hetland added.
Tourists were among those killed in recent weeks.
Backcountry skiing has become increasingly popular over the past few years, with more and more people venturing into the backcountry. But this change in and of itself “doesn’t necessarily lead to an increase in fatal avalanche accidents,” Pillmeier said.
This is because many of these people are often snowshoe hikers who typically avoid rugged terrain. Meanwhile, backcountry skiers are better educated about avalanches, have better equipment and enjoy more organized mountain rescues, she added.
Although conditions remain dangerous, experts advise people to read avalanche forecasts, ski with local expert guides and choose shallower slopes when off-piste.
Snow won’t remain this dangerous forever.
Pillmeier expects the situation to calm down in most parts of Switzerland over the next week once the fresh snow stabilizes, except in southern Switzerland, where there is less snowfall.
However, Bornet expects the danger to continue for several weeks as the snow remains unstable in some parts of France.
