Skier triggered avalanches in the new snow in Middle Basin

Middle Basin
Northern Madison

My partner and I toured over from Beehive into Middle Basin today (saw your car in the parking lot) and finding relatively dry snow in the shade headed for a west facing chute on the ridge that divides Middle and Bear Basins. The chutes walls kept it mostly shaded all morning and it was mostly cloudy as we started skinning up its apron. We had no cracking or signs of cohesion as we approached and a relatively easy boot pack up the chute. A couple of hand pits on the way up showed little cohesion within the top layer and a fairly dry snowpack underneath. We made plans for sluff management with protected spots to let it pass on both sides of the chute. While stomping out a platform we were able to kick off boot sized chunks of snow with no reaction My partner dropped first and his first turn kicked off a storm slab a couple of inches thick from his skis a few feet to his right against the wall of the chute. After a jump turn into a ski cut to one of those protected spots, he triggered a larger storm slab about 4” thick that propagated from the edge of our boot pack on one wall of the chute to the other wall about 20/30’ across and then ran the rest of the chute onto the apron about 300’ below us. No one was caught or injured. We skied out of the chute on the crust bed surface and spent the rest of the day enjoying some low angle trees. The chute was around 40° at 9,000’-9,500’ and west facing. We also noted a point release on an east aspect at about 9,300’ off the ridge separating Beehive and Middle Basin. It looked like a block of snow fell from a south facing cliff onto the slope below. 

Number of slides
Number caught
Number buried
Avalanche Type
Soft slab avalanche
Trigger Modifier
c-A controlled or intentional release by the indicated trigger
R size
D size
Bed Surface
I - Interface between new and old snow
Problem Type
New Snow
Slab Thickness
4.0 inches
Vertical Fall
Slab Width
Slab Thickness units
Single / Multiple / Red Flag
Single Avalanche
Advisory Year