This past week, a snowboarder suffocated to death in a tree well at Oregon's Mt. Hood. (See here
for the story.) He went off a jump and landed head-first in the tree well. Friends spent 15 minutes digging him out, but by then he had already suffocated to death and ski patrollers were unable to revive him.
This is a scary reminder to watch out for tree wells and other hidden hazards, especially in deep snow that otherwise seems harmless. And skiers can fall victim to tree wells just as often as snowboarders. (I know this isn't much of a problem at most Mid-Atlantic resorts, but most of us try to head for deep powder resorts as often as we can.)
There is a good article on tree wells here
written by Craig McNeil. It's worth reading.