Stepped near edge of cornice, skier weight produced shooting crack, dropping cornice debris onto slope below into start zone. Slab avalanche propagating into wind loaded rocky feature nearby. 20m wide by 80m long, 20-40 deep. Eventually loosing momentum in soft slap lower on slope, not full path. A mix of storm and wind slab on top of old cornice. No involvement. No good photos due to poor lighting. Good skiing otherwise.