---
title: "avalanche"
tags: 
- 
---

link: https://www.youtube.com/watch?v=-luspmL_f1o

- Lower risk
- Avoid avi terrain
- safety gear
- what to consider
- using a guide


Reducing risk
- total avoidance (dont go backcountry at all)
- avoidance lite (avoid all avalanche terrain)
- recognising risk, accepting it, minimizing exposure 
- use bulletin

avoidance
- 	stay in bounds/on piste
- 	use low angle slopes
- 	steep: 30-45 degrees

minimize exposure to risks
- know if you are in avalanche terrain
	- maps, guidbooks, photos
	- clinometers
	- _quality_ level 1 course 

Use the bulletin forecast
- low
- moderate : natural avalanches not likely, man made avalanches possible if you ski in the wrong spot
- considerable: if you ski in the wrong spot, human triggered avalances are likely

no overhead hazard: not below a large face or something

avalanche problem:
- persistent weak layer
- wind drifted snow

whumpfs under skis: collapsing snow, avalanches likely

## Video 2
link: https://www.youtube.com/watch?v=1r0YIgdjm6M

lots of different types of avalanche. loose vs slab, wet vs dry.

usually: strong snow over weak snow.

strong: often wind effect: ltighly bonded grains
weak: light snow with no wind and cold clear nights

important: slope angle 

## Snowpack tests
link: https://www.youtube.com/watch?v=OvwhuP4qtQg

- compression test
	- locating instabilities near surface
	- 30(upslope not horixontal) x30cmx110cm ()
	- ![](https://i.imgur.com/ebmXC6M.png)
	- tap 10 times with finger tips
		- mark factures as easy
	- level column
	- tap 10 times with finger tips from elbow
	- level
	- tap with hand or fist from shoulder
	- ![](https://i.imgur.com/2sCLTuz.png)
	- ![](https://i.imgur.com/YT6hWpT.png)
	- facture types video: http://vimeo.com/30996756
 
- deep tap test
	- similar to compression test but tests only for weak persistent layer relatively deep in the snowpack
- extended column test
	- same as compresion test but 90cm wide not just 30cm
	- ![](https://i.imgur.com/itugyJ1.png)

- rutschblock test
	- ![](https://i.imgur.com/FnocAmt.png)
- propagation saw test
- shovel shear test
- hand shear test

equipment
- shovel
- probe
- snow saw
- ruler
- cord

## uptracking and route selection
link:https://www.youtube.com/watch?v=RAXgSoSUD3Y

avalanche triangle: snowpack, terrain, weather.

terrain
- ![](https://i.imgur.com/31KOLSD.png)
- 5 red flags: "natures freebies"
	- recent avalanches
	- shooting cracks
	- recent wind loading
	- recent snow
	- thaw, snow snails
	- debris in creeks

snowpack
- ![](https://i.imgur.com/huT2fni.png)

weather
- ![](https://i.imgur.com/7zMk1mx.png)

alptruth
- ![](https://i.imgur.com/EIoOczr.png)

stay far apart so you dont all get trapped. 

uptracking
- ![](https://i.imgur.com/fs8b8Vm.png)
- use google earth

steepness
- ![](https://i.imgur.com/TNsm8Wd.png)
- caltopo
- hill map


100 with hand vs 1 snow pit

human factor
- familiarity: assuming this are safe because they have been in the past
- acceptance: allowing desire for acceptance (of others) to override decision making process
- consistency: fear of appearing indecisive,
- expert halo: deferring automatically to the expert
- tracks/scarcity:allowing desire to have your day out to influence decisions


**develop a routine**



## Weather and snowpack: slab avalanche formation
avalanches are about timing: know when to go
terrain is like a railway track: safe or not safe

snowpack
- can the snow slide
- layered snowpack
- ingredients
	- slope
	- slab
	- weak layer
	- trigger
	- also
		- initiation
		- propagation
- weak layers
	- new snow
		- storm
		- wind
		- direct-action: hours-days
	- persistent weak layer
		- depth hoar
		- surface hoar
		- near-surface facets
		- persisten: weeks-months
- temp changes during storm can create instabiliies
	- upside down: cold then warms up
	- right side up: warm then cools
	- ![](https://i.imgur.com/7zoi5Z7.png)
- weak layers between storms
	- more persitent hazard
	- depth hoar
		- easy to see when you dig deep enough
			- fall apart in hands
			- sugary
		- ![](https://i.imgur.com/TvBlaC0.png)
		- deep in the snowpack
		- forms the base of the snowpack
		- forms early season
		- formed by thin early season snowpack and cold temps
		- ![](https://i.imgur.com/bPduxfH.png)
		- creates vapour pressure gradient / temperature gradient
			- ground is about 0 degrees c
			- surface is similar to air temp e.g., -10c
			- 10c per m gradient
			- with a shallow snowpack and the same temps. the gradient is higher, causing _faceting_ creating sugary crystals
			- deeper snowpack lessens the gradient
				- less rapid vapour transfer
				- 
	- near surface facets
		- hard to see
		- small grains with sharp angles
		- develop near surface during cold clear nights and warm sunny days
	- surface hoar
		- frozen dew
		- large feathery crystals
		- deposition of moisture on snow surface
		- ![](https://i.imgur.com/pvsVjwG.png)
		- ![](https://i.imgur.com/g3zwefO.png)

weak ≠ unstable (weak + slab + steep)

loading
- new snow
	- rate of loading is important
	- 2 feet overnight is bad
	- 2 feet over a week is good 
- wind
	- can be 10 times faster than from sky
	- cornices
	- large drifts
	- harder snow
- rain
	- adds weight and stress and destabilises


looking at weather:
- bullseye data
	- recent loading
	- recent avalances
	- shooint cracks
	- rapid warming
	- collapsing

![](https://i.imgur.com/qrlmp8g.png)

snow pits only give you one data point

spatial variability exists

snow on the ground in always changing

strong over weak = BAD

rapid change = BAD