Slide occurred about 200 feet below the top and was triggered sympathetically at the rollover by the second skier descending on the lower angle skiers left ridge. Could not safely inspect the crown but it appeared to be about 2 feet and the slide occurred on basal faceted snow. The slide moved slower than expected and went further than expected at about 500 feet. We experienced significant collapsing throughout the area throughout the day. Key lesson learned was not that a slide occurred in that location, but that it traveled further than expected taking out the tracks of the first two skiers as they wrapped around to the exit.