Clamshell remote cornice sz 2.5+

Went up and down the low angle supported SE shoulder of the Clamshell. On the final approach to the summit, the second person on the skin track heard a deep low pitch noise on the north side of the shoulder but could not see any sign from its location. On the way down the shoulder, it was noticed that approximately 200m long of cornice had failed and triggered the persistent slab sitting on the Feb 3 crust. The remote trigger distance was estimated at 20m. It was impossible to see how far down the north face the resulting avalanche had ran but given the terrain, it likely ran over 500m vert.