A ski guide was preforming a ski cut on a N aspect today at 8,200'. They triggered a reactive soft slab that was 100 feet wide and ran 500 feet long. It ran on a knife hard melt freeze crust. This crust formed overnight when the old moist snow froze hard. Multiple ski cuts were preformed on similar slopes with no result. This avalanche had good spatial continuity that did not exist in other start zones.