Persistent Slabs Where Persistently Slabby

We went to monitor the persistent slab problem and recent wind loading in the Canyon Creek area.

• We got shooting cracks, whumpfs, and triggered 2 small persistent slab avalanches on northeast and even southwest facing test slopes at between 5,600' and 5,800'. All of that feedback was the result of collapsing the surface hoar layer buried about 1.5 feet deep. All the places we could trigger the surface hoar had slightly denser, wind affected snow above, making the slab a little stiffer.
• We found a skier triggered persistent slab avalanche several days old at the same elevation, around the corner on a northwest aspect.
• We found the buried surface hoar layer widespread on shady aspects, and we experienced a large whumpf in a flat, shaded opening at 6,400'.
• On exposed, sunny slopes above 5,900' we lost the surface hoar layer and found a thin sun crust buried instead. We dug a pit on one of these slopes and got no propagation in our stability tests. We found facets above and below the mid January crust at this location.
• Recent up slope winds had stripped away much of the snow above the January crust in the tops of south-facing chutes.
• The sun triggered a few very small sluffs on solar aspects and the top inch of snow was becoming moist on those slopes.'
• We got some minor cracking in recent wind drifts that did not have surface hoar buried underneath.

We managed the persistent slab problem by choosing low risk terrain: no convexities, low slope angles. The powder we skied without having to sweat the avalanche hazard was well worth the self discipline.