Kindergarten couloir

We dug a pit at the entrance of the couloir, and found a thick crust around 25-30cm below soft snow. When we did collapsing test no break or signs of instability were found. We think something triggered the avalanche like cornice falling, rock fall or something else created the avalanche high above and hit us once we were bookpacking 30m above the entrance luckily. One of us got carried away through the runway for 100m and I was able to find shelter before it hit us. No one was injured, only one lost pole. Came down after.