Avalanche: Lake Desolation 2/25/2010

Observer Name:

Bruce Tremper

Observation Date:

02/25/2010

Occurrence Date:

02/25/2010

Occurrence Time:

Unknown

Region:

Lake Desolation
Mill D North
Big Cottonwood Canyon
Salt Lake

Avalanche Characteristics

Elevation:

9200'

Aspect:

West

Slope Angle:

Trigger:

Unknown

Trigger: additional info:

Intentionally Triggered

Avalanche Type:

Hard Slab

Weak Layer:

Surface Hoar

Depth (avg):

20"

Width:

35'

Vertical:

50'

Snow Profile

Snow Profile Comments:

The surface hoar was buried about 1.5 - 2 feet deep and was very sensitive. Compression tests were inconclusive but you could easily find it on a shovel shear test. The Extended Column Test propagated with medium elbow taps. This surface hoar is over 3 weeks old and it's clear that it is not going away very quickly. Every time we load some weight on it, it continues to produce sensitive avalanches.

As the slab above it becomes thicker and stiffer, it will produce avalanches that are much more dangerous and unmanageable. Watch out.

General Comments

See photo gallery

I ski cut a small breakover and triggered a 1.5-2' deep slab on surface hoar. 1.5' x 35'. West facing, 9,200', 35 degrees. We were able to trigger some of the hangfire as well. It was quite sensitive and the surface hoar was plainly visible on the bed surface as well as in the profile.

One other skier descended the slope next to the one where I triggered this avalanche and they did not trigger anything, although it was the same aspect, elevation and steepness as the small rollover where I triggered the avalanche. This shows the pockety nature of buried surface hoar.

We saw several natural, shallow, soft slab avalanches at lower elevations along the creek bank in lower Mill D North on steep, east-southeast facing slopes. These were 6 inches of new snow sliding on a pre-existing sun crust. I could not find any surface hoar involved but they certainly acted like it. We saw one slide while skiing up and 3-4 others nearby when we skied down that were not there when we skied up. There was a high precipitation intensity in the morning, which, no doubt, contributed to the shallow instability. Also, the sun poked out at times, which may have added to the stress.

Video 1: