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. 30 th 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 11 th & 12 th 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 LooseSlab

Form of track UnconfinedChannelled

Position of sliding surface Full depthSurface

Type of movement AirborneFlowing

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 Wright A chance in a Million? Scottish Avalanches by Bob Barton & Blyth Wright ISBN Websites