Public Observation
Observation Details
Observation Date:
March 23, 2021Submitted:
March 24, 2021Zone or Region:
Tamarack Out of BoundsActivity:
Skiing/SnowboardingLocation:
Lone Tree, South of Tamarack ResortTriggered Avalanches
Did you trigger any avalanches?
YesWas it intentional?
NoAvalanche Type:
Soft SlabSize:
Size 1: Relatively harmless to peopleElevation:
7600 & 7500FTAspect:
SComments:
I am humbled to say I triggered two avalanches yesterday. One was intentional from a ski cut, the other was unintentional. Both were on the south side of Lone Tree. The first was around 7600', true south aspect, 30 degree slope angle right above a convexity that quickly increased to 35 degrees, 35'x450' (fall), WL-ASc-R1-D1.5-I-4-6". Second was around 7500', just SE of true south, 30-32 degree slope, 100'x200' (fall), WL-ASu-R2-D1.5-I-4-6".Signs of Unstable Snow
Observations
Both of these incidents occurred within 15 minutes of each other, just after 12PM. The air was still cool, just below freezing in the shade and -5C on the snow surface. Strong solar radiation, north winds were howling on the opposite side of Lone Tree, but the south side was nearly dead calm. This was not a wind slab problem. There was 4-6" new snow sitting atop a stout crust supportive to the weight of a skier. This new snow failing to bond to the previous interface was the problem. The new snow skied nice and was just beginning to moisten (no evidence of wet snow releases). Here's the funky thing: both of these slides fractured and propagated, then they acted as wet loose slides. It appeared the new snow was just starting to get moist and was not bonding at all to the previous interface. I also noticed persistent grain types atop the crust and below the new snow. There appeared to be either some buried surface hoar and/or near surface facets sitting atop the crust. I could hardly skin back up a 30 degree slope without sliding.
These incidents spooked me. New snow sitting atop a crust is a red flag. New snow getting moist sitting atop a crust is a bigger red flag. New snow getting moist atop a crust with a persistent grain type is scary. Yesterday was an excellent learning experience and thankfully we dodged some bullets. It's easy to get complacent with the transition to spring. A brief return of winter demands winter avalanche senses. I re-read yesterday's advisory this morning. Sometimes the most obvious problems are right in front of our faces. Here is what the advisory stated yesterday:
"The new 6-10 inches of snow over the past few days has brought back winter, but the Spring Sun is coming out to change things once again. Our new snow is resting on slick crusts, and not bonded well on steep Solar aspects. Below the new snow, the bonding of recent saturated layers is pretty good, and the snow below is hard. For now, we are concerned with the new snow that has formed variable wind slabs and loose avalanche problems. "
Media
