Observation: Turnagain

Location: Tincan

Route & General Observations

Up to treeline at 2300′ and down the far skiers right side of Tincan tree runs. Stopped to dig a couple pits on the way down to check on the status of the faceted weak layer.

Weather & Snow Characteristics
Please provide details to help us determine the weather and snowpack during the time this observation took place.

Mostly overcast throughout the day. Temps were in the teens to twenties with calm winds.

Snow surface

At lower elevation (below ~1500') the surface was settled powder with 3mm SH on top. Above 1500' in the surface was variable with wind effect ranging from supportable to breakable to soft.


We dug pits in three locations to check on the facet/crust weak layer combo. The snowpack was largely the same at 2300' on a SW aspect and 1700' on a NW aspect, with a right side up slab on top of the faceted weak layer buried about 100cm. The faceted layer in both pits was one finger hardness and the faceted grains showed signs of rounding. At the 2300' pit there was a thin wind crust on the surface which broke easily on a layer of decomposing new snow in our ECT but did not propagate. The faceted layer was not initiated by the ECT either.

At 1700' we tried a few improvised stability tests that we hoped would be better for testing deeply buried weak layers. We performed a deep tap ECT - which means we set up a normal ECT and then removed the snow under the shovel down to 15cm above the top of the faceted weak layer (see photo). This is a variation of the ECT and Deep tap test which is not normally used. Even with the shovel 15cm above the faceted layer we did not get propagation in the weak layer. It took 22 taps to initiate a failure in the top of the faceted layer and 24 taps for the middle of the faceted layer (see photo), but neither failure propagated across the column.

We also performed a cross slope PST (CPST) which is the same as a normal PST but the isolated column runs across slope instead of up slope. With this test we got PST 35/100 END in the top of the faceted layer and PST 50/100 END in the middle of the faceted layer. Neither of these are normal tests and we were mostly just playing around with different methods to access our current weak layers.

At 1200' we dug a pit the turned out to have an alder branch running straight through it (not ideal). We did not find the faceted layer here but we were surprised to find moist facets within a melt freeze crust sandwich at the bottom of the snowpack.

Photos & Video
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