Heavy snow in the West is contributing to some of the worst avalanche conditions on record. Seven snowmobilers were killed in an avalanche in the Canadian Rockies.

Four more who tried to help the trapped men were caught in a second avalanche.

Three of that group survived, clawing their way out from underneath the snow. Fearing another slide, they walked down the mountain, where they were found by rescuers.

Conditions are perfect for more avalanche activity.

"You have denser snow on top of weaker snow and when you put that on a slope and you add a trigger, you're looking for a recipe for an avalanche," Meteorologist Kenny Kramer explained.

One of the snowmobilers is still missing. Rescuers say they will stay on the mountain until he is found.