Matt Primomo

Salt Lake » Park City Ridgeline » No Name Bowl

North No Name Ridge

9,000'

Northwest

33°

Skier

Hard Slab

3'

200'

Unknown

While touring up North No Name Ridge, I was able to show my students in a Level 1 course an undeniable sign of instability. While approaching an open patch along the ridge we got our first whumph, a 20m diameter collapse, but no cracking evident. I sent one of my students first to experience it... nothing. We followed and as three of us came in close proximity of each other, WHUMPH! The entire open area collapsed and a fracture propagated down to the slope below (remote trigger). We dropped a good 5cm. The slope below had many tensile cracks, but it didn't move. We spent a good amount of time checking out the fracture line. Investigation revealed a 1m to 1.5m slab sitting atop the MLK rain crust. This is an area where the MLK crust was on the surface until last week. There was 40cm new snow F hardness sitting on 20cm of 4F snow, this all on a 50cm pencil hard windslab, with the dust layer evident at the base. Right below the dust layer was the friable 0.5cm MLK crust (what was left of it), and below were 4mm striated cups, F hardness to the ground for about 70cm. CT scores varied widely from failure upon isolation to CT30, depending on the depth of the pencil hard slab. The consistent part of the test was the shear character, a Sudden Collapse. This was a great demonstration of the highly variable nature of this deep persistent layer, a low/moderate probability, but with high consequences. Sorry no photos...