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On February 17, 2026, a deadly avalanche hit the mountains near Lake Tahoe in California. A big storm had just dumped heavy snow on the Sierra Nevada range. This created a very fragile and dangerous environment for skiers. Tragically, the snow buried a group of backcountry skiers and their guides. Six skiers were saved safely, but eight people lost their lives. One person was still missing when the report was made. Just before the crash, the Sierra Avalanche Center issued a high-danger warning. This alert told everyone that the risk was extremely high that day.
Avalanche deaths are rare inside managed ski resorts. Professionals there constantly watch the snow and manage risks for everyone. However, the danger grows much larger when skiers go into the backcountry. These are wild areas without professional safety staff. In the United States, thirty backcountry avalanche deaths were reported during the 2022–23 season. The numbers stayed very high with sixteen deaths the next year. There were also twenty-two deaths in the 2024–25 season. These numbers show a growing danger for those who go into unpatrolled snow.
Nathalie Vriend is a physicist and skier at the University of Colorado Boulder. She studies the science of how avalanches move and break. Her work helps connect physics theory with real-world safety tips. She believes that understanding the science is the key to survival. Knowing how the mountain works helps skiers stay alive in danger.
The way an avalanche moves depends on the snowpack structure. This is one major part of the problem. An avalanche happens when all the wrong conditions line up at the same time. It is a mix of factors that turns a quiet slope into a moving wall of death. The angle of the mountain slope is a main factor for danger. Slopes between 25 and 40 degrees have the highest risk. It is strange that these are also the best angles for skiing. If a slope is less than 25 degrees, small snow slips may happen. But the snow usually will not gain dangerous speed. If a slope is steeper than 40 degrees, snow often cannot build up enough. This naturally removes some of the avalanche hazard.
A trigger is also needed to start the slide. A snowpack can look stable until a skier, snowmobile, or rock adds force. Strong winds or falling rocks can also start the movement. Blowing snow can build up into large overhangs called cornices. When these cornices fall, they can cause a huge avalanche below. This shows how a small event can start a huge chain reaction.
Mountain snow is not the same everywhere. It is a complex history of the whole season. Snow builds up over time, so it acts like a record of the weather. It has both stable and weak layers inside it. Fresh snow is light and fluffy with crystal shapes. However, when temperatures rise, the snow melts and then refreezes. This changes it into a grainy, icy substance.
This icy layer is often a weak link. When new, heavy snow falls on top, the weak grains can slide apart. This creates a slippery surface. The weight of the new snow can make a whole mountain face slide away fast. As the avalanche speeds up, it picks up more snow and rocks. It becomes larger and more violent very quickly.
In my lab, we study small avalanches to see how they work. We use a method called photoelasticity. This creates thin layers of snow to show the forces inside. We track the particles with a high-speed camera. They bounce and hit each other very fast, in just one-thousandth of a second.
In a real avalanche, these hard hits create heat from friction. This causes more snow to melt inside the mass. When the avalanche stops, the water can refreeze fast. It can then freeze the snowpack solid like concrete. Common advice says to "swim to the surface." But a buried person may get confused and not know which way is up. If the snow is still moving, you might move slightly, but it is very hard.
I did research in Switzerland where we caused avalanches on purpose. We watched from a safe bunker while explosives blew up the snow. Radar showed us inside the avalanche moving toward us. It traveled at speeds over 110 miles per hour. Even a small avalanche is hard to ski or run from. The biggest danger is deep snow where a person gets buried. As the snow slows down, more snow piles on top of the victim. Survivors say it feels like being trapped in concrete. You cannot move your limbs at all. It is a terrifying experience with no room for mistakes.
Backcountry skiers carry special gear to help them survive. But your friends are your best resource. Emergency helpers might take hours to get to remote areas. Time is the most important thing in a rescue. Several tools are needed for safety. First, always carry an avalanche transceiver. This device sends a radio signal to show your location. If you are caught, the device keeps sending your signal. Friends can switch their devices to find your signal quickly.
It is also vital to carry a shovel and a probe. When a person is found, the snow is very hard. A shovel is needed to dig them out. Avalanche air bags can also help survival. A skier pulls a handle to inflate a big bag behind their head. This makes the person larger in the snow. Larger things tend to rise to the top during an avalanche. This makes the person easier to find.
This is a big question for winter sports in the future. Warmer temperatures do not just mean less snow and fewer avalanches. Mountains with changing temperatures may have more melt and freeze cycles. These cycles create weaker snow layers. This makes the terrain more unstable than in the past. The old safety rules based on history may change fast. In 2017, a massive avalanche in Italy destroyed a whole hotel. It happened in a place where history said no avalanche would occur. This proved that past data is not always a safe guide.
Scientists use computer models to guess where avalanches might happen. But as weather changes due to climate change, the causes become complex. The rules of the mountain are changing. Skiers and experts must stay alert and ready to adapt.