Reactive Hard slab on N aspect below East Nai

First Skier stopped near the bottom of a small concave slope on N aspect, just west of the chute below East Nai. Second skier followed and while joining first skier on concave slope, broke a thin crown over head, we heard a loud crack. Slab travelled down hill only a few meters before stopping due to the uphill swoop at the bottom of the concavity. Interestingly the debris at the bottom of the slab travelled uphill a bit before stopping. Slab was very hard and broke across adjacent features but did not travel far given the concave nature of the terrain. We suspect that the trigger point was a thin part of snow near an ice bulge.