David Williamson captured this video of a rockslide while hiking up the Middle Teton in 2013. His friend, Phil White, became trapped by boulders as he was pummeled with debris. Read more about the accident and hear Phil's account here.
Watch: Glacier Calves in Wrangell-St. Elias National Park and Preserve, Alaska
What does it look like when a house-size chunk of ice crashes into the water just a few hundred yards away from you? Watch and see.