Wind Slabs on Andesite

Walking from the car to the Castle/Andesite trailhead we could see blowing snow and feel strong NE winds. We noticed small cornices and wind loading on W facing slopes next to the I80 overpass. We stopped to check out how much new snow had accumulated and how it was bonding to the old snow surfaces in a sheltered area near the trailhead. We found about 30 cm (12 in) of cold, soft, light new snow on top of old refrozen snow surfaces. Quick hand pit observations indicated that the snow had not bonded well to the old snow surfaces. We also found some very small (less than 5 ft tall) but steep test slopes and were able to cause the storm snow to sluff off of these mini slopes as mini loose dry avalanches.

We continued up sticking to low angle terrain. We encountered strong NE winds and intense blowing snow as soon as we entered open areas. At times visibility decreased to a couple of meters. On a E-NE facing near treeline slope, we saw firm scoured surfaces. Just above this slope on a lower angle W facing slope, we found large drifts of snow up to 1m (3 ft) in depth. Stepping onto the drifts triggered collapses and shooting cracks up to 10m (30 ft) long. The weak layer was a softer layer of storm snow at the base of the wind drifted snow. 

We continued up to the top of Andesite Ridge via a low angle route. The NE winds increased in strength and we saw more drifted snow on SE-S-SW-W-NW aspects. Stepping on these drifts on low angle slopes continued to produce collapses and shooting cracks. We chose not to test any steeper wind loaded slopes. We also encountered more scoured surfaces on N-NE-E facing slopes. The winds got strong enough to blow us around as we approached the summit of Andesite. Needless to say, we quickly retreated to more sheltered terrain. While skinning to our transition area, we detoured to look at a steep less wind-affected slope to see if it had any signs of activity on it. A ski kick on low angle terrain at the top of this slope pushed some snow down onto the steeper part of the slope where it picked up speed and entrained the storm snow in a small loose dry avalanche (details here). 

All these signs of instability reaffirmed our plan to stay on low angle terrain. During our descent, we could still feel the crust below the new snow when we turned. We felt the crust less on the lowest angle parts of the descent.