Scottish Avalanches

January 2010

• What is an avalanche?• What do you need for an avalanche to occur?• How to avoid?• What to do if caught?• What to do if you see?• Sources of information?

What is an avalanche?

• An avalanche is a rapid flow of snow down a slope, from either natural triggers or human activity.

Avalanches can happen to you

• Having accepted this, you have greatly reduced your chance of ever being involved in an avalanche.

Three killed in avalanches in Scottish Highlands

• Two climbers were killed in an avalanche on Ben Nevis, and a third died from his injuries after being swept away in another avalanche in Torridon, Wester Ross.

• 30th December 2009

Avalanche activity in the Pentlands

• Full depth avalanche activity noted on the southern slopes of Carnethy Hill

• Further minor sloughs noted on Scald Law• Creep lines noted on Turnhouse Hill• Significant week layers in the snow-pack identified at

several locations 11th & 12th January 2010

What do you need for an avalanche to occur?

• Snow• Slope• Instability• Trigger

Snow

• How much?• Where is it lying?• Transportation• Slab (hard & soft)• Metamorphism (freeze thaw – sub zero)• Consolidation• The 24 hour rule

Slope

• Angle (30-45)• Orientation• Size• Terrain• Convex and Concave• Avalanche Classification

Type of release

Loose Slab

Form of track

Unconfined Channelled

Position of sliding surface

Full depth Surface

Type of movement

Airborne Flowing

Instability

• Sliding surface• Temperature• Firmness• Wet/Dry• Other• Significant difference in snow pack

Trigger

• Natural• Human

How to avoid: Part 1

• Information• Weather reports• Avalanche reports• Personal reports (blogs, word of mouth etc)• Avalanche observations on the day• Snow pits = history

How to avoid: Part 1

• By the time you set foot on the snow you should have a pretty good prediction of what conditions will be like, what level of hazard exists and where it is likely to be located. Your field observations modify and update this prediction and apply it to the specific case and/or location.

How to avoid: Part 2

• Don’t go out• Do you have to cross?• Above and below• Route choice• Islands of safety• One at a time• Terrain traps

Avalanche Risk Assessment

• Could the slope avalanche?• Is the slope stable or not?• What could happen if it did avalanche?• Are conditions getting better or worse?• Is there anything you can do to prevent avalanche accident?• What is the likely hood of injury?• What can you do to minimise the risk?• Is the risk worth taking

The four critical factors

• Accumulation – is there sufficient snow on the slope?• Terrain – is the slope steep enough? Is there a

convexity?• Weak layer – is a weal layer present in the snow-pack?• Trigger – are you going to go on the slope?

What to do if caught in an avalanche?

• Preparation• Delay departure• Get rid of kit• Shout• Swim or roll• Fight for the surface or an air pocket

What to do if you see an avalanche?

• Personal safety, check for further danger• Mark last location of victim• Count the survivors• Quick search• Thorough search• Send for help

Sportscotland avalanche information service

• Since 1988• December to April• 5 areas• Actual reports for day• Forecasts for the following day• Weather forecast dependent• Weather wrong = avalanche forecast wrong• Do not rely on as only source of info• No substitute for what you see or find on the hill

Sources of information

• Books• A chance in a Million? Scottish Avalanches by Bob Barton & Blyth W

right • ISBN 0 907521 59 2

• Websites• http://www.sais.gov.uk/index.asp• http://en.wikipedia.org/wiki/Avalanche