Sunday, 20 February 2022

A Rough Slightly Tongue in Cheek Guide to Snow Science

Snow science seems to be in vogue and nothing wrong with that. But - most folk are not avalanche forecasters just Joe average trying to make good decisions. I like to simplify it when discussing so here’s a white board session from a  picture taken on a course I ran some time ago when the powerpoint projector failed and I had to cuff it:

Mountaineers are seldom "searchable". At "The Gate" Glencoe. Spot Probe Finds 😢

  • The avy forecast is an area forecast. The local risk may be different + or –
  • Read the forecast and its nuances, snowpack history and snow profile – and the blog. They have done 80% of the work for you. You decide the rest
  • Terrain choice is a big deal, Angle, Aspect and Altitude, Complexity, Commitment and Consequences
  • Water becomes ice or something along a continuum
  • Snow has branches which break up if transported by the wind
  • More wind more break up, denser pack i.e Slab
  • Graupel is not hail which is a laminate but is a ball of softish ice. Graupel are ball bearings with similar effects with new snow on top. They also eddy into rock features causing local weakness. Rocks can be Islands of safety or a landmine. 
  • The deeper you go down the snowpack the less cold it gets until at ground level its zero or just above. Mice shrews and invertebrates live there. 
  • Water vapour rises through the snowpack.
  • Crystals can grow/regrow in cold conditions either on the surface as hoar or within the snowpack as hoar/re growth.
  • Avalanche forecasters measure the snow temperature every 10cm. If the temperature is greater than 1c in 10cm going up the snowpack then the snowpack is getting weaker. Less then overtime it will eventually get stronger, Strong gradients grow facets, weak gradients make rounds.
  • In rain, thaw, warmer weather crystals round off sometimes joining to each other.
  • Wet snow is Water logged snow and can flow like a concrete river down gullies, corries and obvious slide paths. Beware spring thaws or after heavy rain.
  • Wind blown slab snow shears or collapses on a layer underneath and just like rice crispies there's a snap, crackle and pop
  • Whump is the sound of air escape from under the slab, the snap.  If it doesn’t pop go buy a lottery ticket as your lucks in.
  • Windslab most often requires a trigger. You are the trigger and the pop!
  • Snow pits should be kept simple. The SAIS and other forecasting services in alpine countries do the heavy lifting. They are only relevant for the couple of  square meters where you dig. They are good places to take stock, talk and communicate. The data might confirm what you see but also might not. Its hole in the snow. The armpit test is fast and repeatable. Dig out a small hole and above cut out as deep a column as you can with a ski end, pole or shovel. Pull on it to see if the surface slab is bonded to the underlying snowpack.
  • The progression of survival probability such as % survival at a given time is a statistic. You could survive a couple of hours if in the miracle headline group, but more likely dead from hypoxia in less than 4 minutes. Bear in mind of ski patrollers getting to fully buried victims in alpine resorts fast, giving BLS with fast helo access and ALS from dedicated SAR Docs, and taking the victims to specialist centres, most victims do not survive to discharge
  • A shovel is an airway opening device
  • If you are not searchable your fucked 
  • That's about it really

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