Observation: Public
Observation Details
Name:
Mike RolfsObservation Date:
January 9, 2021Submitted:
January 10, 2021Zone or Region:
East CentralActivity:
Skiing/SnowboardingLocation:
East of Mission RidgeTriggered Avalanches
Did you trigger any avalanches?
YesWas it intentional?
NoAvalanche Type:
Soft SlabSize:
Size 1: Relatively harmless to peopleElevation:
6110Aspect:
NComments:
I triggered and was carried by an avalanche. Elevation: 6110 Aspect: NNE Slope angle: 40 degrees Time of day: 12:50pm Temp: 24F Width of avalanche: approx 60 feet Length of avalanche: approx 80 feet Run length of debris pile: approx 500 feet (I was only carried about 50 feet)Photo:
Observed Avalanches
Did you observe any avalanches?
YesAvalanche Type:
Soft SlabSize:
Size 1: Relatively harmless to peopleElevation:
6200Aspect:
EComments:
The only other avalanche activity I saw this weekend east of Mission Ridge was an avalanche below Bomber cliffs today. This is the same avalanche location reported on 12/ 31 by Anthony Lubetski. Wind transported shallow soft slab over surface hoar. Ran approx. 300 feet, mostly did not entrain additional snow but did trigger another slab mid-run. Both avalanches this weekend were minor in nature, but dangerous in location and there is no information in a pit that prepares you (me) for this type of avalanche. The problem is isolated, hard to spot, and exists above the surface of the snow column in a pit.Photo:
Signs of Unstable Snow
Observations
Although very small, the avalanche that I triggered had the potential to be very dangerous due to the terrain that it ran through. It was a soft slab caused by wind deposit over previous night's surface crystals which were widespread. 1-1/2" crown stepped down to storm layer roughly 6" down. I was carried about 40 feet and was able to maneuver toward a pinnacle which stopped me. I was buried to my armpit against the rock on the uphill side but had full use of my downhill side. I was able to self extract. I observed a crack in the bed surface with vertical and downhill displacement of about an inch suggesting that the avalanche stepped down to one of the crust sandwiches but did not propagate. This would be consistent with recent tests where the 12/21 crust will fail in isolated column tests in mid 20's but won't slide off the block. I returned to the site the next day to dig across the crack to study this crack. Wind transported snow obscured the crack, and where I dug was not the right spot. Later photo study showed I was 2 feet downhill from the crack. Found 3/4" columnar crystals between the moist soils and the bottom of the snow-pack. Otherwise, the snow-pack matched other locations in the basin with isolated column test failure in top 6 inches on hand taps that would not slide off the block, and failure of the upper crust sandwich on full arm taps that also would not slide off the block. (Test location slope angle 40 degrees). The avalanche ran approx 500 feet and did not appear to entrain further snow. Directly following this incident, I observed similar avalanche 200 feet south on same terrain feature. I suspect remote trigger from deep failure of 12/21 crust caused by the avalanche that I triggered, but of course I don't know. The photo below is of the suspected remote trigger avalanche with debris from mine visible on the right.
Media
