We hear the scary stories. We see the sobering signs posted around every resort. But maybe you haven't seen just how terrifying a tree well can really be, even at the base of a smaller tree. Hopefully this informative post from CMH Heli Skiing will remind you that it's not only avalanches we have to worry about in and out of bounds.

RELATED: A Successful Tree Well Rescue at Sun Valley

Tree wells form when snow accumulates around the base of a tree but doesn't fill in the area beneath the lower branches or near the trunk. This can create a massive yet invisible hole for skiers and boarders, often large enough to topple them in head-first. Snow Immersion Suffocation, or SIS, is a real hazard when it comes to tree wells because not only has the skier fallen in a large hole, their collision with the tree has most likely knocked more snow down on top of them from the branches above.

Tree wells present one of the most dangerous hazards in and out of bounds. Mammoth photo.

Not only should you ride with friends in the trees, you should also keep an eye on them at all times. Many tree well accidents occur because partners never saw where their friend fell. Check out these tree well safety resources before your next big snow day adventure.