[EarnYourTurns]

In The Silence of the Lambs, Hannibal Lecter said, “we covet what we see every day.” And so it was, after driving to work every day, coveting the unnamed cirque immediately east of Mount Aire, that Steve and I slogged 90 minutes up the Lambs Canyon trail, to have a look.

HASTY PIT RESULTS:
Layer 1: 3 inches, of wet, unconsolidated, faceted snow.
Layer 2: 12 inches, 2F hardness wind slab.
Layer 3: ½ inch P hardness crust
Layer 4: 20 inches of 2F hardness consolidated snow
Layer 5: 30 inches of faceted depth hoar, all the way to the ground.

TESTS
Shovel shear tests revealed easy failure at the Layer 4/Layer 5 interface, which was consistent with deep slab instability in the area. The quality of the shear was not “clean.” Since layer 2 was so hard, pole probing had its limits, even handle side down, even putting plenty of effort into probing.

OBSERVATIONS
Evidence of wind loading, both small cornices rimming the cirque and the characteristics of the slab. Settlement cones observed during the ascent, but the ascent was up a drainage with a southerly aspect (see below for slope characteristics). Some small cracks observed skinning along the leeward side of the cornice. Some small wet slides activity in the immediate area, on a more easterly aspect (040-060 degrees). These appeared to be point-release slides, limited to the top layer, not entrained.

SLOPE CHARACTERISTICS
Aspect was N (005 degrees). Slope angle 35 degrees. Unknown anchor quality, with nothing significant protruding. On the sub ridge, where we did our pit testing, we only noticed rocks, dirt, and small vegetation (sorry, Gary was right – I’m not a botanist)

WEATHER:
Temperature inversion in the area. 30 degrees at the trailhead (6700ft, 1130 MSTt) and 50 degrees at the summit (8500ft, 1330 MST). Sunny skies, no wind.

AVY ADVISORY:
From the UAC, 1/20/05 “The avalanche danger is moderate on slopes of about 35 degrees and steeper. Human triggered avalanches are possible. The avalanche danger will rise to considerable with daytime heating, especially on and below steep sunny slopes. A considerable avalanche danger means human triggered avalanches are probable and natural avalanches possible.

DECISION:
I guess these two “punks” didn’t feel “lucky,” since we bailed off the ridgeline. It was enough to get some exercise in the sunshine, above the Salt Lake City shitmosphere (the inversion layer).

Comments?

[cesare]

Sounds a lot like a Colorado snowpack. I back off stuff like that all the time. If there had been an option at less than 30 degrees, however, I might have given that one a go--but that air temperature and the UAC forecast would sure make me wonder about what was happening to the bonds between layers 2 and 3 as well, even on a north slope.
_________________
that sounds like a sure-fire way to get bitch-slapped by devil's club -- dschane

[Rebob]

First of all, I'm from the Wet Coast, so that profile already looks alien in nature, but I'll offer the following.

There's no way I'd go onto that slope.

The angle of the slope (nearly prime for slabs), the inversion to 11C, the wet layer on top (what would the skiing be like anyway?), and the likelihood of weaker bridges in the snowpack (spatial variability) would suggest to me that it would be better to take up knitting that hit that slope. Besides, I'd expect that there would be something more lingering around that crust near the top of the pack.

If it were 20 degrees?

[Gary Brill]

earnyourturns,

I think the inversion and structure are the two keys. The structure shows abrupt changes in grain size and hardness, so the warming should cause the various layers to act differently, redistributing stress and strain. That could make failure at or below the thin crust or at the base of the snowpack more likely. The lack of a clean shear on depth hoar is to be expected. The depth hoar often fails within the layer, rather than at its boundaries. I must say, though, that because of my Maritime homeground, there are many who are more familiar with the behavior of depth hoar than I.

The structure looks at best fair. There are significant variations in properties of the layers. Warming may increase stress. You're on a south aspect where it may warm more dramatically. I think, depending on your snowpack history, I might prefer a cooler aspect.

[Rebob]

Gary, I believe the aspect is north, but the approach was from the south.

[dewam]

This falls under my "GO Big" rule. If it does go, it could easily kill. Backing off leaves the opportunity to ski for many more years. Den

[wow]

Shovel shears are not an indication of stability, but simply a method of identifying weak layering.
The shear was not clean or Q1, leaving some question as to the results and the next step would be compression testing and a r-block. Until those are done, the answer to go or no go remains unknown.
It doesn't appear loading was enough to produce avalanche, but observations of the area and natural activity would be a further indication.
Time of day would be important with perhaps an earlier arrival leading to upper layering without the dampness.
Decision to go or no cannot be made with the current data.
I'd be interested in the time of day and why a complete hasty pit with testing of the weak layering concerns was not done.
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[EarnYourTurns]

Wow asked: I'd be interested in the time of day and why a complete hasty pit with testing of the weak layering concerns was not done.

We started digging at about 1330 MST. Honestly, between the cracking, little wet slides, time of day, and the way the damned block jumped into my lap during the shear test, we'd pretty well decided to play the chickenshit card. Ordinarily, the RBlock is next, but that seemed like a waste of time, given the circumstances.

And yeah, we did kick ourselves for not getting an eariler start. Sweet Jesus, it got hot, FAST yesterday!

Gary mentioned we were on a south aspect. Sorry for any confusion. Approach was from the south, aspect faces north (heading 005).

[wow]

I'd guess, given the time of day, the elevation and the presence of a layer you felt concerned about, the northwest face of Mt. Aire would have been a better option. Excellent run but a hell of a funnel in the starting zone, also requiring a long flat track back to Lambs through the brush.
I found upper elevation westerly aspects to remain firm into late afternoon.
11'000 feet is a bit higher than 8500 with inverted temperatures more pronounced in Parly's than Little Cottonwood, it seems.
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[Gary Brill]

earnyourturns:

[smitchell333]

My take:


Bottom Line: Bailing is always safer - you made a safe choice.

The critical things for the decision I noted are
- Slope angle
- Known possibility of a slab layer of significant size- both from the avy report and the pit.

A R-block test would have likely told you what you needed to know. Although I've found in these conditions you very well could've triggered a shear just by standing above your pit on skis even w/o isolating the column.

You could have considered a low angled option if available.