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DPS

Concerning snow pack

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I went up to Chair Peak last two Saturdays.  I noticed a hard, 1/4" thick layer of ice under the snowpack.  Last Saturday it was covered by 12" of unconsolidated snow.  The steep slopes in Chair basin had slid below the SW Chimney all the way to the hard layer. 

I personally find the persistent sliding layer unusual for the Cascades, and I don't think the warm, wet weather this week will do much to consolidate the snowpack to the sliding layer or below it.  I am concerned that the sliding layer will persist throughout the winter causing high avalanche danger until some kind of event or change in conditions bonds the ice layer to the layers below and above it.  Please be mindful as you head out into the backcountry this weekend that avalanche conditions appear to me to be uncharacteristic of the Cascades.  Be safe out there.

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I agree on this. Unless we get a gnarly rain event that decimates our snowpack, we might have that persistent layer for quite a while.

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I read something by NWAC, I think on IG, that basically said the same thing in that we need some major rain for long term stability. A Bellingham based photographer got swept over a cliff in an in-bounds slide the day before opening at Baker, but thankfully he was fine.

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My friend and I were skiing in bounds at Mission Ridge and saw a skier drop in and set off this avalanche (in bounds).  The crown was 5 feet tall in its biggest area.   The skier escaped and was very lucky.  

 

Avy.thumb.jpeg.ce41ea3fbc00f840b703b40f0f27f130.jpeg

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I suspect that layer was the result of that November snow followed by weeks of sun and freeze thaw. Not that unusual for the first couple of snow events to slide on it. A month of dumps will bury it real good. But don’t let my human factor heuristic kill anyone 

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some thoughts from a retired professional - I spent twelve years as a professional avalanche "hazard mitigation"  ( a far more accurate terminology than the typically used "control") worker at Stevens Pass, Squaw Valley, and Mammoth Mountain, as well as forty years ski-mountaineering in Idaho, Wyoming, Colorado, Oregon, Washington, California, Montana, & Alaska.  This winter presents conditions rarely encountered in the PNW.  NWAC reports a 1"-2" thick layer of faceted snow (surface hoar) currently buried under more than 4' of newer snow.  A layer buried that deep is very likely to persist for the remainder of the winter.  As the snowpack above this layer consolidates, it's morphing into a 4'+ thick hard slab, which will trigger unpredictably, and on many slopes will run in historic volumes.  Historic volume slides have already been reported at Mission Ridge and Crystal Mountain, indicating that even explosive-controlled and ski-compacted slopes must be considered at risk.  I have personally witnessed slides of such volumes destroying stands of mature timber - even areas historically considered reliably protected may not be so  this year.  Such conditions also present a hazard most of us never consider:  those of us who use snow pits to assess travel hazard know to dig them in "representative" locations - sites that approximate a starting zone, but with a "safe" runout.  My favorite pit protocol is the ruschblock, for its viscerally impactful interpretation protocol.  But this year, preparing a "representative" ruschblock would expose the digger to working below a  ski-length-wide column of 4'+ thick hard slab supported on a 1"+ thick layer of facets - a probable collapse of enough snow to bury the digger -- sobering prospect...  this may be a season when the only slopes we may consider "safe" are those that have already slid on that buried layer... just sayin...

-Haireball

 

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To add to what Curt said, even slopes that have slid on the weak layer can be repeaters, in that the weak layer gets buried again after a slide, and continues to be dangerous. Hopefully thats less of an issue as the weak layer is so thin. Just make sure to check first and not get lulled into a false sense of security.

Bummer that the snowpack sucks this year, but at least it's the first time it has happened in eons. Living in the rockies seems like every October we get a foot or so that becomes sugary garbage and hoses any chance for solid stability for the rest of the season. The old nothing is going to rip but if it does the entire snowpack slides and everyone dies scenario. Stay safe out there! Skiing is tight, dying is not.

Edited by keenwesh

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Thanks all. Naive question: when a slab cuts loose and the weak layer rides down the harder layer underneath it does the harder layer have some melting due to friction? If so, does it re-freeze and actually increase its hardness, thus increasing the chance of future slides down to that base level? Or is the hard base layer somehow perturbed in such a way that new slides down to it are unlikely? 

In any case, it sounds like this could be a very dangerous year in the PNW both in bounds and out of bounds. Bummer. 

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Come on Rad didn't they teach you that in Chem 140? (Moles of water * density / enthalpy of water) / (angle of slope * speed)

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33 minutes ago, Rad said:

Thanks all. Naive question: when a slab cuts loose and the weak layer rides down the harder layer underneath it does the harder layer have some melting due to friction? If so, does it re-freeze and actually increase its hardness, thus increasing the chance of future slides down to that base level? Or is the hard base layer somehow perturbed in such a way that new slides down to it are unlikely? 

In any case, it sounds like this could be a very dangerous year in the PNW both in bounds and out of bounds. Bummer. 

If there's a layer that's a moisture barrier buried within the snowpack, such as a raincrust, and the weather is clear with big temp fluctuations between night and day facets can develop on the crust where the moisture gets stuck and can't move through the snowpack. That's generally an early spring continental snowpack thing though. Dry air draws moisture up out of the snow. Happened within 48 hours of some buddies skiing the skillet on Moran. Was not psyched to discover an extremely reactive death slab after skinning 8 flat miles across the lake in the dark, but the choice was clear. Made 1500 ft of lazy turns back to the lake, and turned our feet into hamburger slogging right back to the car while sledneckers ripped past us at 60 mph.

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update:  the buried faceted layer appears to have failed to survive two weeks of rain & warm weather.   last week the Cascades had rain up to 7000+'.  trips to the Funnel in Icicle Canyon, and to Chair Peak show little evidence of that layer surviving below about 4000'.  haven't been higher, so don't have data for higher altitudes...   but NWAC reports significantly moderated avalanche hazard...

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