Benzene Alley

Found 40 cms  (16 inches) of new snow at sea level and 50 cms at 1200'.  New snow was dry and uncohesive in the morning and became top heavy as the day went on and temperatures warmed.  New snow has formed a slab that is sitting on buried surface hoar that formed during the last week of nice weather.  This buried surface hoar is sitting directly on a rain crust creating a dangerous setup.  All of the key ingredients for avalanches to occur were present: a slab, a reactive weak layer, and a bed surface.

The weak layer was found to be very reactive with large collapses and long shooting cracks observed.  As the temperature warmed and the slab stiffened signs of instability increased.  We had well over 100 collapses on our tour, some of the being very large travelling a few hundred feet.   The setup we saw today would likely produce human triggered avalanches on slopes steeper than 30° and remote triggered avalanches were possible.  Did not travel on slopes steeper than 30°.

Stability tests were concerning at 1200' on a NW aspect.  We received propagation upon  isolating the column in both ECT and PST tests. 

Observed one slab avalanches that had pulled out from a rollover barely steeper than 30° around 1300'. The slide was small but involved most of the terrain feature. Heard one natural come off of Benzene peak, overcast skies limited other avalanche observations. Shooting cracks and collapsing were widespread and significant.