www.avalanchetraining.info - Foundation Theory Presentation

Course Aim Same slope, different day… … why is there a difference?

Incidents

First Question: What do you need for an avalanche?
Answer:
1. Snow, 2. Slope and, 3. a Trigger
Corresponding Foundation Course content:
Snow profiles and field tests
Formation of the snow pack
Influence of weather
Influence of terrain
Triggers
Avalanche types

Second Question: How do you avoid being in an avalanche?
Answer:
Information, 2. Observation, and 3. Decision Making
Avalanche forecast and danger scale
Weather forecasts
Route details and planning
Observations on arrival and on the route
Decision making and risk reduction
Survival strategies

Third Question: What do you do if you are involved in an avalanche?
Answer:
1. Observe, 2. Organise, and 3. Search & Emergency Care
How transceivers work
Search exercises
Probing and digging
Emergency procedures
Emergency care

Has various shapes and sizes
Falls to the ground at different times and under
different weather conditions
Different layers of snow have different properties.
It is layers with very different properties that are the source of slab avalanches. Snow

The effect of weather on the snowpack Snow

Snow Often there are a mixture of ‘good’ and ‘bad’ changes happening at the same time. Unless it is colder than - 40°c snow is always changing. Some changes make the snow more stable, some changes make it less stable.

The weather changes the snow pack. Most changes from the weather are at or near the surface of the snowpack, but changes at or near the bottom can create a high risk.  Wind  Temperature  Solar radiation  Precipitation Snow

Snow Snow moved by the wind causes windslab

Snow Rain and high temperature Massive ice avalanche on Mt Blanc du Tacul caused by heavy rain and warm temperatures ‘ Normal’ ice avalanche on Mt Blanc du Tacul

Snow Direct sun (solar radiation)

Strong or rapid onset
Long duration
Intensifying clouds
Dense snow or rain
3cm or more of snow / hour
30cm or more in a storm
Strong enough to move snow
Long duration
Windslab on slopes we want to ski
Near or above 0 o C
Rapid changes
Snow Weather critical values Precipitation Temperature Wind Solar Radiation

The snow pack changes over time. These changes can be ‘good’ or ‘bad’ depending upon the:  Temperature  Depth of snow Snow

Changes over time due to the temperature and depth of snow Deep snow and ‘warm’ (e.g. -1 to -5) = more stable  (i.e. a ‘weak’ or ‘low’ temperature gradient (less than 1 °C per 10cm depth of snow) results in rounding and bonding) Shallow snow and very cold = less stable  (i.e. a ‘strong’ or ‘high’ temperature gradient (more than 1°C per 10cm depth of snow) results in crystal growth) Snow

Rounding and bonding makes the snow pack more stable and occurs when: The snow pack is deep and air temperatures are warm (e.g. -1 to -5) The critical value for rounding is a temperature gradient of less than 1 °C per 10cm of snow depth Snow

Crystal growth happens on the surface (hoar frost) or in the snow pack (depth hoar) Snow

Depth hoar creates a very weak layer and occurs when the snow pack is shallow and the air temperatures are very cold The critical value for crystal growth is a temperature gradient of more than 1 °C per 10cm of snow depth Snow

Snow Cover
Very weak layers
Large, loosely packed, or
angular snow
Strong layers above weak
At or above 0 o C
Moisture present
Weak strength
Smooth sliding surfaces
Snow Snow Pack critical values
Thin
Highly variable
Layers Bonding

Slopes  0 o – 15 o (e.g. a green run) - rare for avalanches start (main danger would be from any steeper slopes above)  15 o – 25 o (e.g. a blue run) - o ccasional avalanches start  25 o – 30 o (e.g. a red run) - s ome avalanches start  30 o – 45 o (e.g. a black run) - m any avalanches start (all types and sizes, dry and wet)  45 o – 50 o (e.g. extreme ski) - Many loose avalanches start, often dry, some slabs  50 o + - fewer avalanches start

Slopes Aspect (direction the slope faces) N

Slopes Slope aspect in relation to exposure to the sun

Slope Aspect in relation to wind direction Wind direction Windslab forms on ‘lee’ slope

Buffalo Mountain – north-east aspect Wind from the south-west

Buffalo Mountain Note the tracks, and the point where the slab released.

Triggers - human About 90% of fatal avalanches are triggered by the victim or another member of the party

Triggers - natural Trees and rocks heated by the sun

Triggers - natural Trees and rocks heated by the sun Convex slopes and rocks

Types of Avalanche

European Avalanche Classification Length>1000m Vol>10000 m3 Could bury and destroy trucks or trains, large buildings and forestead areas Runs over flat areas (significantly less than 30°) of at least 50 m in length, may reach the valley bottom 4. Large avalanche Length<1000m Vol<10000 m3 Could bury and destroy a car, damage a truck, destroy a small building or break a few trees Runs to the bottom of the slope 3. Medium avalanche Length<100m Vol<1000 m3 Could bury, injure or kill a person Stops within the slope 2. Small avalanche Length<50m Vol<100 m3 Relatively harmeless to people Small snow slide that usually cannot bury a person but push over a cliff 1. Sluff Size Damage Runout Term

Loose Snow

Avalanche Activity When? Have avalanches occurred Critical = current or recent Where? Are they running, or did they run Critical = on terrain similar to your path Why? Triggers Critical = any natural or human triggered How? Characteristics of failure layer Critical = loose grains, angular crystals

Avalanche Start Zones
Also:
Triggers
- Ground cover
- Slope support
 Incline – how steep is the slope?  Aspect – which direction does the slope face?

Avalanche Terrain Indicators Vegetation clues

Avalanche Terrain Indicators Debris clues

Terrain Traps Trees Rocks Cliffs Streambeds Depressions Glacial moraines Any terrain features that could increase the consequences of being caught in an avalanche.

Slope angle is greater than 30 o Slope aspect is in the lee of the wind Trigger points are around or above Terrain traps are around or below Avalanche Terrain Critical Values

What type and trigger?

What types and triggers?

What type and trigger?

What types and triggers?

Where are the hazards and ski descents? A B

Where are the hazards and ski descents? A B C

Where are the hazards and ski descents? A B

Basic Safety Equipment Transciever Probe Shovel Navigation First aid Repair Survival Communication

Chance of survival for buried victim over time 93% within 15 minutes 26% after 45 minutes

Speed of rescue and safety equipment used BEACON ONLY BEACON & PROBE BEACON & SHOVEL 59 mins Duration of beacon search Duration of probe Duration of digging ARVA ARVA et SONDE ARVA et PELLE BEACON, PROBE & SHOVEL Time in minutes ( depth of burial 1 metre )

Speed of rescue and safety equipment used BEACON ONLY BEACON & PROBE BEACON & SHOVEL 59 mins 50 mins Duration of beacon search Duration of probe Duration of digging ARVA ARVA et SONDE ARVA et PELLE BEACON, PROBE & SHOVEL Time in minutes ( depth of burial 1 metre )

Speed of rescue and safety equipment used BEACON ONLY BEACON & PROBE BEACON & SHOVEL 59 mins 50 mins 25 mins Duration of beacon search Duration of probe Duration of digging ARVA ARVA et SONDE ARVA et PELLE BEACON, PROBE & SHOVEL Time in minutes ( depth of burial 1 metre )

Speed of rescue and safety equipment used BEACON ONLY BEACON & PROBE BEACON & SHOVEL 59 mins 50 mins 25 mins 15 mins Duration of beacon search Duration of probe Duration of digging ARVA ARVA et SONDE ARVA et PELLE BEACON, PROBE & SHOVEL Time in minutes ( depth of burial 1 metre )

Avalanche Transceivers Signal Pattern

Searching with Avalanche Beacons Primary Search Secondary Search Pinpoint Search

Primary Search First phase needs to cover the burial area quickly

Secondary Search
Grid Method
Used with analogue transceivers.
Once a signal is detected a more methodical technique is needed

Secondary Search
Induction Method
(used with digital transceivers)
Once a signal is detected a more methodical technique is needed

Pinpoint Search
Fine grid
Once within 2-3m a very methodical technique is needed in combination with the an avalanche probe
Same system for both analogue and digital transceivers.

Questions? Summary and conclusions Programme for tomorrow

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www.avalanchetraining.info - Foundation Theory Presentation

by Roger Payne on Jan 30, 2009

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www.avalanchetraining.info - Foundation Theory Presentation — Presentation Transcript