Triggered a slide on the east facing approach to Lake Peak. Slide triggered approximately 100 feet above us and carried two skiers for about 150 feet and slowed due to a flat spot in the terrain. The slide propagated for approximately a half mile around the northside then all the way around the peak across Lake Chute. If we were not approaching from the safest possible route avalanche could have been much worse as the north facing portion of the slide ran for over 1000 feet.