A group of riders in Ephraim Canyon were on Philadelphia Flats poking around a bit. One of them got stuck and other riders were helping. Yet another rider from the group came past when the group felt the snow suddenly drop and said it sounded like a "sonic boom". A cornice release hundreds of feet away from them. What happened is they collapsed the weak sugary faceted snow at the base of the snowpack. Once the collapse was initiated, it continued to collapse the weak layer away from them just like dominos. The video below shows test results with the same setup. This will happen all over the Skyline when people start venturing out. All you need is a steep slope and you will trigger an avalanche.