Descending to Saskatchewan Glacier from the Pat Sheehan traverse, first two out of party of four crossed on foot without incident below wind loaded pocket following bench-like supported feature, following recent tracks, to safe zone in rocky moraines. Third person, on skis, cut slightly into bottom of the pocket, triggering slab with a crown 50m above. Skier was taken for a ~300m ride down to runout zone coming to rest above surface. Fourth person descended safely to moraines. Very fortunate to have no injuries, minor loss of gear. Poor communication from leader, varying experience levels, and false comfort from previous tracks were factors in the incident.