The above video is from the helmet cam of a snowmobile rider who gets buried by an avalanche. At the beginning you see the sheet of snow he's on start to give way. He rides it for a bit, but then hits a tree and gets flipped over and buried. You don't see much after that except the snow he's buried in until he gets dug out.
The guy was lucky the managed to dig him out so quick. About 60% of people who get buried in an avalanche die (although around 90% survive if they're dug out in the first 15 minutes as he was). Along with hypothermia, the big killer is asphyxiation because the warm breath melts the snow which refreezes as ice and allows for the build up of carbon dioxide.