GREENVILLE, N.C. (WNCT) — If you’re taking a trip to go skiing or snowmobiling, avalanches are something you might worry about.

They are a backcountry recreational person’s worst nightmare. Few things are as terrifying as millions of tons of ice and snow breaking off a mountain and racing down at highway speeds.

There are two kinds, dry slab avalanches and wet avalanches. Dry slab avalanches are by far the most dangerous. They happen when a cohesive slab of snow slides off of the layer underneath it.

A video from the National Avalanche Center shows how a skier can escape the slab at a 45-degree angle, but if the slab breaks up first, there’s nowhere the skier can go. 

On average a little over two dozen people in the United States die from avalanches every year, according to the Colorado Avalanche Research Center. The key to saving an avalanche victim is digging them out fast. According to the Utah Avalanche Center, 93% of avalanche victims who are dug out within 15 minutes survive, but the odds begin to decrease rapidly after that.