Booting up Y Couloir today and a wet slide released from the top. My ski partner and I were not terribly far up it (less than 1/3 I would guess) and we heard a rumble. We looked up and saw a wall of snow and immediately ducked into a crack between a rock on the right wall and the couloir and stayed tucked into this lifeline for the duration of the slide. Once everything settled we descended, moving from safe spot to safe spot keeping our eyes and ears open. We did not see any new bootpack from today but had observed tracks from the day before. We also did not observe anyone below us during our ascent. We were very lucky.