Unstable Results on Buried Surface Hoar in Deep Creek

Location Name: 
Deep Creek
Region: 
Cabin Creek, Deep Creek, or Pole Creek Area
Date and time of observation: 
Thu, 01/14/2016 - 12:00
Location Map: 
United States
39° 14' 38.76" N, 120° 15' 28.512" W
See map: Google Maps
US


Red Flags: 
Recent avalanche activity
Whumphing noises, shooting cracks, or collapsing
Recent loading by new snow, wind, or rain
Observation made by: Forecaster
Snowpit Observations
More detailed information about the snowpack: 

Buried surface hoar existed on some slopes in Deep Creek, but we were unable to find evidence of it on other slopes. The Jan. 13th surface hoar layer was buried about 12-14 inches down with the Jan. 9th surface hoar layer about 1-2 inches below that. Above these buried surface hoar layers, a layer of dense heavy wind affected snow existed. Tests on slopes with surface hoar resulted in unstable Extended Column Test results in which fractures that started when surface hoar broke would propagate across the column (ECTP18, ECTP15, ECTP17, ECTP14 on N-NE facing slopes between 6400 and 8200 ft). On slopes where we could not find the surface hoar, ECT's did not produce propagating results. Since we could not reliably determine which slopes would have the buried surface hoar layers, we stuck to low angle or thickly treed slopes. 

Wind slabs and cornices above wind loaded test slopes did not react to a skier's weight from a distance, but we avoided getting too close to the edges of cornices or stepping out onto wind loaded slopes due to the potential wind slab and surface hoar combination. Wind loading continued today and blowing snow was visible along all the ridgelines. Wind slabs and cornices continued to build throughout the day.

Photo 1: 4-8 mm surface hoar from the surface hoar layer buried on Jan 9th. This sample was taken from the bottom of the slab after one of the ECT's failed. 

Photo 2: Active wind transport along the Sierra Crest. 

Snowpack photos: 
Weather Observations
Blowing Snow: 
Yes
Cloud Cover: 
50% of the sky covered by clouds
Air temperature: 
Below Freezing
Wind Speed: 
Strong
Precipitation: 
None
Air temperature trend: 
Cooling
Wind Direction: 
Southwest