each year, avalanches claim numerous lives. skiers or even backcountry hikers get covered in a wall of snow in a valley or on a mountainside. basically, avalanches occur when there is more stress on the top layer of snow than on the bottom layer. in winter and spring, experienced and novice skiers alike frequently search for fresh powder trails. on ski mountains, it is not uncommon for skiers to deliberately ski outside the marked boundaries of trails. avalanches can travel at up to 300 km/h and carry with them thousands of tons of snow. being trapped in an avalanche is the worst fate imaginable. if you are buried underneath several meters of snow, you will run out of oxygen and suffocate. after 35 minutes, a person has only a 30 percent chance of survival.