Approach to Armchair Glacier Avalanche

Working our way to lower part of armchair glacier through the trees and came to a small gully to cross. The treed slope we were ascending was very crusty and wind scoured. We saw signs of slabbing in the top 3 cm, but below it was very firm. Entered the gully below a convex roll to traverse and remotely triggered a shallow slab 30m above spanning the gully immediately. Slab was formed from wind deposited snow. Carried by avalanche for 250m, and run out stopped another 150m below.