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240 lines
5.4 KiB
Markdown
240 lines
5.4 KiB
Markdown
---
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title: "avalanche"
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tags:
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-
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---
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link: https://www.youtube.com/watch?v=-luspmL_f1o
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- Lower risk
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- Avoid avi terrain
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- safety gear
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- what to consider
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- using a guide
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Reducing risk
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- total avoidance (dont go backcountry at all)
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- avoidance lite (avoid all avalanche terrain)
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- recognising risk, accepting it, minimizing exposure
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- use bulletin
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avoidance
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- stay in bounds/on piste
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- use low angle slopes
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- steep: 30-45 degrees
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minimize exposure to risks
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- know if you are in avalanche terrain
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- maps, guidbooks, photos
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- clinometers
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- _quality_ level 1 course
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Use the bulletin forecast
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- low
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- moderate : natural avalanches not likely, man made avalanches possible if you ski in the wrong spot
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- considerable: if you ski in the wrong spot, human triggered avalances are likely
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no overhead hazard: not below a large face or something
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avalanche problem:
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- persistent weak layer
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- wind drifted snow
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whumpfs under skis: collapsing snow, avalanches likely
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## Video 2
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link: https://www.youtube.com/watch?v=1r0YIgdjm6M
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lots of different types of avalanche. loose vs slab, wet vs dry.
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usually: strong snow over weak snow.
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strong: often wind effect: ltighly bonded grains
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weak: light snow with no wind and cold clear nights
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important: slope angle
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## Snowpack tests
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link: https://www.youtube.com/watch?v=OvwhuP4qtQg
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- compression test
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- locating instabilities near surface
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- 30(upslope not horixontal) x30cmx110cm ()
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- 
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- tap 10 times with finger tips
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- mark factures as easy
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- level column
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- tap 10 times with finger tips from elbow
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- level
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- tap with hand or fist from shoulder
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- 
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- 
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- facture types video: http://vimeo.com/30996756
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- deep tap test
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- similar to compression test but tests only for weak persistent layer relatively deep in the snowpack
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- extended column test
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- same as compresion test but 90cm wide not just 30cm
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- 
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- rutschblock test
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- 
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- propagation saw test
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- shovel shear test
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- hand shear test
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equipment
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- shovel
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- probe
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- snow saw
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- ruler
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- cord
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## uptracking and route selection
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link:https://www.youtube.com/watch?v=RAXgSoSUD3Y
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avalanche triangle: snowpack, terrain, weather.
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terrain
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- 
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- 5 red flags: "natures freebies"
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- recent avalanches
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- shooting cracks
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- recent wind loading
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- recent snow
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- thaw, snow snails
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- debris in creeks
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snowpack
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- 
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weather
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- 
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alptruth
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- 
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stay far apart so you dont all get trapped.
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uptracking
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- 
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- use google earth
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steepness
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- 
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- caltopo
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- hill map
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100 with hand vs 1 snow pit
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human factor
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- familiarity: assuming this are safe because they have been in the past
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- acceptance: allowing desire for acceptance (of others) to override decision making process
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- consistency: fear of appearing indecisive,
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- expert halo: deferring automatically to the expert
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- tracks/scarcity:allowing desire to have your day out to influence decisions
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**develop a routine**
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## Weather and snowpack: slab avalanche formation
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avalanches are about timing: know when to go
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terrain is like a railway track: safe or not safe
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snowpack
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- can the snow slide
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- layered snowpack
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- ingredients
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- slope
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- slab
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- weak layer
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- trigger
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- also
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- initiation
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- propagation
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- weak layers
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- new snow
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- storm
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- wind
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- direct-action: hours-days
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- persistent weak layer
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- depth hoar
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- surface hoar
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- near-surface facets
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- persisten: weeks-months
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- temp changes during storm can create instabiliies
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- upside down: cold then warms up
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- right side up: warm then cools
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- 
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- weak layers between storms
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- more persitent hazard
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- depth hoar
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- easy to see when you dig deep enough
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- fall apart in hands
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- sugary
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- 
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- deep in the snowpack
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- forms the base of the snowpack
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- forms early season
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- formed by thin early season snowpack and cold temps
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- 
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- creates vapour pressure gradient / temperature gradient
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- ground is about 0 degrees c
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- surface is similar to air temp e.g., -10c
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- 10c per m gradient
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- with a shallow snowpack and the same temps. the gradient is higher, causing _faceting_ creating sugary crystals
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- deeper snowpack lessens the gradient
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- less rapid vapour transfer
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-
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- near surface facets
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- hard to see
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- small grains with sharp angles
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- develop near surface during cold clear nights and warm sunny days
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- surface hoar
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- frozen dew
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- large feathery crystals
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- deposition of moisture on snow surface
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- 
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- 
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weak ≠ unstable (weak + slab + steep)
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loading
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- new snow
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- rate of loading is important
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- 2 feet overnight is bad
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- 2 feet over a week is good
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- wind
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- can be 10 times faster than from sky
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- cornices
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- large drifts
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- harder snow
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- rain
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- adds weight and stress and destabilises
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looking at weather:
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- bullseye data
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- recent loading
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- recent avalances
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- shooint cracks
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- rapid warming
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- collapsing
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snow pits only give you one data point
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spatial variability exists
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snow on the ground in always changing
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strong over weak = BAD
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rapid change = BAD
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