Friday, December 18, 2009

snow pro

okay, two pits dug off baby's butt.   12/17/09

first, N40degreeE
incline 35
elevation  6030
air temp .5C
precip, light snow
foot penetration  waist

154 cm depth
nov 28 ice layer at 94 cm - 2 cm thick, not decomposing whatsoever
snow pack temps were cold above ice layer, then warming considerably below, this could be a problem later
a weak bond between new light snow on top of ice layer, from beginnning of the week, and the newest, heavier snow, from the last two days. this was at 110 cm.  this layer may dissapate over time. i expect it will.
thin weak layer at 73 cm.  breaking thru the 94 cm ice layer could propogate down to this layer.  but if something goes on this ice, there is trouble anyway.
there are other ice layers below this. again, if they are failing due to propagation, there is big trouble already.
we had mixed results in our compression tests.  first went at CTM 3, Q3.  so, we thought, not too bad considering the circumstances. this failed at the 94cm ice layer
second test failed while cutting the column.  about as bad as it gets.
what we found interesting was it was failing below the ice. the entire ice layer was breaking off in the compression test.  hum?  any comments?
we did an extended column test, to examine likelihood of propogation.  chances are our techniques were not the best, but we did find moderate propogation.

so we skied a highly treed slope, very carefully, and immediately had one huge settlement.  but no fracture or settlement lines.  then nothing else.  it skied okay, but very heavy, with a super punchy layer.   skied dropping below the ice layer can easily get caught and take a skier down.  this of course would be trouble.  so we skied WAAAAY in the backseat. 

second pit
S130degrees SE
slope 28 degrees

133 cm depth. 
november 28th ice at 76 cm
weak bond between light and heavy snow at 109 cm.
again, mixed results on column tests, but mostly it failed easily at 76 cm.  mild propogation below.
on this exposure, the snow was failing above the ice, and we found faceted crystals, 2 cm lying on top. htis seemed much more normal, to me.
so, given the angle, plenty of anchors, and a slope known to not slide, we skied this without event. it skied quite well.  it did take me a couple of turns to get used to the heavy snow, after skiing inbounds fluff monday and tuesday.
so, not a professional  report by any means, and not much differnent then we expected.  it still remains.  avoid open slopes over 30 degrees, on all aspects.  this could take a lot of time and snow to become safe, if it ever really gets safe.  but you know, weighing ones options of pleasure vs. pain.

great fun last night at the Crush.  thanks brian, mike, ryan. and all the readers.  (even though some were a bit long winded).  looking forward to the reading.  and for the rowdy crowd in the back, and a few others, maybe we need a reading with tomatoes and eggs and a medieveal aspect.

okay, i am out for the weekend.  hope the snow settles and then continues.  lets get as many turns in as possible before the masses arrive. 

1 comment:

  1. Ok, you asked for it, here I go...

    Chances are the well established ice lens is trapping moisture being moved vertically through the snowpack by pressure gradient... Once the vapor reaches the buried ice lens, it is trapped creating a warm, vapor saturated environment and large T gradient between the ice lens and snow interfaced immediately beneath it... These conditions can produce well defined facets with very poor cohesive properties immediately adjacent to the ice lens... IF you care, technically the process is called "Kinetic Metamorphism."

    The bonding on top of the ice lens must be of better quality... It is possible that where you were for your second stability test (probably right next to the first test- welcome to spatial variability), snow that fell on top of the lens had minimal T gradient between it and the ice lens and bonded better than the snow that is decomposing beneath it... It would be my guess decomposition is not taking place on this interface because the snowpack environment is not vapor saturated and the T gradient remains within the confines of destructive metamorphism (rounding)...

    Oh, the "settlement" you are referring to is probably related to the piss poor quality snow (facets) beneath the ice lens... AND, it's actually is NOT settlement...

    The noise and sometimes movement you feel is "catastrophic failure- aka "Whumping...” Technically, this is failure occurring at a weak layer/ slab interface at greater than 20 m/s...)

    The reason it didn't avalanche is probably because you were either in the right place (lots of anchors and/or in low angle terrain) or there was not enough energy stored at the interface of the slab/ weak layer interface.

    Don't you worry, whenever I am surprised by a "Whump” I say "Did you feel that F'n SETTLEMENT!

    Ok, now with all that said, I would once again like to pitch my safety message and say if you are headed into the backcountry to recreate this weekend or in the near future, be conservative, have a solid partner, have a plan, know your line, and escape options if things go bad.

    REMEMBER, expose only one at a time and make frick'n sure you and your party ARE DIALED IN with proper rescue gear and technique.

    Have a safe weekend!!

    Ted Steiner.