Repeater slide

First rider ski cut start zone with no result, rode down 100m to a safe spot. Snow was wind affected and wind slab. Second rider rode past him and triggered a small wind slab. The slab pulled more sluff than expected down with it and it knocked the rider off his feet and removed his board (hard boots). Rider 1 witnessed the second rider get tossed around and then sit upright in the middle of the runout. We were able to ride out unharmed