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Starting Point

Terrain. Starting Point. Simplistic Snow consolidates through melt & freeze Icy layers a hazard Graupel layers a hazard Soft layers potential hazard Profiles look for “different layers” Stability tests look for “IF” but not so much “WHY”. Snow pack. Trigger.

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Starting Point

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  1. Terrain Starting Point • Simplistic • Snow consolidates through melt & freeze • Icy layers a hazard • Graupel layers a hazard • Soft layers potential hazard • Profiles look for “different layers” • Stability tests look for “IF” but not so much “WHY”. • Snow pack • Trigger

  2. Outdoor professionals are more likely to get avalanched than anyone else • Increased probability – time spent in avalanche terrain • Avalanche terrain approaching routes and “getting off” • Route choice (visibility) • Group management conflict

  3. Build on existing knowledge • Not so simple any more • Understand “why we make bad decisions” • “Heuristic Traps” • Make better decisions about the snow • Develop understanding • Jargon Buster • Help find (and understand) further info

  4. Atkins (2001) – In 41 accidents involving “avalanche aware” victims, 83% were due to decision making errors rather than subtleties of terrain or snowpack. Why might Instructors make poor decisions? Heuristic Traps

  5. Heuristic Trap - Commitment • Cue: Prior commitment • Behaviour: Consistency • Trap: Critical change “They’ve paid me a lot for a good day out” “I promised them a walk to a peak this week”

  6. Heuristic Trap - Scarcity • Cue: Limited opportunity • Behaviour: Desire +/ Competition • Trap: Increased risk taking “Let’s get up before that other team beat us” “I haven’t seen good snow on that for 15 years”

  7. Heuristic Trap - Familiarity • Cue: Familiar setting • Behaviour: Same as last time • Trap: Conditions change “I can’t see it but I know there’s nothing above us” “You can always get to the easy track down here . . . . ”

  8. Heuristic Trap – Social Proof • Cue: Other people’s behaviour • Behaviour: Imitation • Trap: They make a bad decision “If they’re going up there it must be okay” “I bet the other team are getting to a peak”

  9. How snow “changes“ (made simple) • The “Melt + freeze” process is easy to understand • Fresh snow “settles” even if it doesn’t melt – How? Why? • Process often called “destructive metamorphism” or: Equi-temperature Metamorphism

  10. Equi-temperature Metamorphism • Equi = “same” • Temperature • Metamorphism = “change” Fresh snow to Firn snow • Temperature <0°C • Snow never “melts” • Firn snow is “real” nevé

  11. Equi-temperature Metamorphism (“Same Temperature Change”) Reproduced from “Winter Skills” by permission from MLTUK

  12. Equi-temperature Metamorphism Reproduced from “Winter Skills” by permission from MLTUK

  13. Often called “destructive metamorphism”

  14. Different snow types • Fresh snow rounds easily (Stellar dendrite) • Graupel rounds more slowly (rimed snowflakes) • Depth hoar struggles to round (facets)

  15. Not all snow falls from the sky • Some crystals grow: • On the surface (surface hoar) • In the Snow pack (depth hoar) • In prolonged cold conditions Surface Hoar

  16. Surface Hoar

  17. Surface Hoar M o i s t a i r • Like dew after an Autumnal frost • Moisture in the air condenses on the cold surface • Slowly grow into pure crystals • Only forms in prolonged clear and cold weather (with no wind)

  18. Surface Hoar • Forms (or “grows”) slowly on the surface in cold clear conditions • Only becomes a problem if and when it is buried by another layer • May have been destroyed by the sun on sunny slopes • May have become a substantial layer on shady slopes

  19. Photo Case Study Crown wall

  20. Photo Case Study

  21. Photo Case Study

  22. Photo Case Study Buried surface hoar (glinting crystals) Super smooth sliding surface

  23. Snow profile

  24. Depth Hoar • Similar process to surface hoar • Moist air from ground or wet snow pack • Meets cold air from above • Crystal growth within the snow pack

  25. Temperature Gradient Metamorphosis

  26. Detached Crust How did this crust form? Why is it not “stuck” to the snow beneath?

  27. Depth Hoar case study Why did it release just here? How come this was safe to decend

  28. Depth Hoar case study Nothing easily visible in profile

  29. Depth Hoar case study • Shallow snow pack • Depth Hoar layer • Steeper gradient • Deep snow pack • Homogenous • Less gradient

  30. Jill Fredston & Doug Fesler Alaska Mtn Safety Center David McClung & Peter Schaerer The Mountaineers Bob Barton & Blythe Wright Scottish Mountaineering Trust Further reading

  31. A Few Facts The colder it is……. The longer its cold for……….. Depth of snow

  32. So What? Hidden layers Thin layers Prolonged cold – worse not better

  33. How to predict Quiz?

  34. Snow profiles

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