Whumpfing only on propagation of avalanche. Performed a few sheer tests throughout ascending and discovered no planar or isolated slabs. The fracture occurred on a shallower snowpack near ridge top (less than 10m).
Avalanche Information
Party traveled very tightly together ascending the couloir to mitigate any momentum from prospective moving snow hitting last partner. Everyone safely arrested as the slab broke at top member's piolet.