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About avalanches

by Robyn Gordon

Why Worry About Avalanches?

Snow avalanches are a natural process, occurring perhaps 1,000,000 times per year, world-wide. They are one way for snow on an incline to adjust to the pull of gravity. The vast majority of these slides are not a problem, because an avalanche, in and of itself, is not a hazard. A person (or a person's belongings) has to get involved in order for there to be a problem.

So, who gets caught in avalanches?

 

What happens if you get caught in an avalanche?

 

The fact is, that avalanches don't drop from the peaks onto the heads of unsuspecting innocents with the unpredictability of a plummeting meteorite. 95% of people who are caught in avalanches are caught by a slide that was triggered by themself or a member of their party.

I think this is good news! Our behaviour creates the hazard, so we can change our behaviour to avoid problems.

Avalanche Characteristics

There are many different types of avalanches, but the one that worries us the most is the "slab" avalanche, in which a mass of cohesive snow releases as a unit. This type is easily recognized by its distinct crown and flanks (click for a diagram of the nomenclature associated with avalanches).

Slab and other avalanches can be hard or soft, wet or dry and can be triggered naturally or artificially.

Spotting Avalanche Hazard: The Avalanche Triangle

Some places have avalanches: Switzerland's Alps, Utah's La Sals, Nepal's Himalayas, New Zealand’s Mountains. Some places don't: South Viet Nam, the Mile-High Stadium, your living room (the distinctions are not always so obvious, unfortunately).

Why is this? Avalanches are formed by a combination of three things that together are known as the "Avalanche Triangle". These 3 ingredients may be present in one location but absent 10 feet away. The three legs of the triangle are Snowpack, Terrain and Weather.

Detecting Instability

There are many tip-offs to the presence of a potential avalanche, including surface clues and active stability tests. You should never trust a single information source--stability evaluation is an ongoing process!

The information from this page originates from www.avalanche.org.




Robyn Gordon
Robyn Gordon

Author



Also in EDUCATIONAL RESOURCES

New Zealand Avalanche resources

by Robyn Gordon

Mountain Saftey Council (MSC) New Zealand

The Mountain Safety Council is an important advocate of outdoor safety in new Zealand. They have an excellent brochure on avalanches, how to recoginise danger and how to prevent them. Their website has further resources available that you might want to explore. It also contains saftey tips for in summer time.

MSC also runs a website with backcountry avalanche advisory which is provided as a public service. It is intended as an advisory only.

Avalanche forecasting is an undertaking which requires extensive study and field observations. Those endeavouring to travel in the Southern Alps and the mountains of the North Island, do so at their own risk. We recommend winter travellers be well informed about current weather, snowpack and avalanche hazards.

Winter travellers should not travel alone. All members of your party should wear a transceiver (457khz) and know how to use it. In addition everyone should carry a shovel, and a probe. Winter travellers should advise someone where they are travelling, and when they will make next contact.

Department of Conservation (DOC)

The Department of Conservation can assist with safety advise. Check their website for more details.

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Risk Management

by Robyn Gordon

Before teachers take classes on snow trips they should have all students fill out a risk assessment forms. This is called risk management.

The forms help to identify all of the possible risks that may occur during the trip. The next step is then to work through scenarios how the grooup will respond in case one of the scenarios happens. Each of the scenario's should be worked through to make sure they have the right equipment, first aid, support systems, and procedures in place before they go.

They are then prepared for every possibility.

The Avalanche Lady covers risk management in her speech and can help school groups with providing the risk assessment forms.

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Conclusions

by Robyn Gordon

Avalanches are a part of the normal cycle of events in the mountains and are not a hazard in general, as they occur away from inhabited areas. It is only when people coming into these environments unprepared or unaware of the risks do avalanches become life threatening.  With 95% of avalanche accidents caused by the people who get caught up in them, it is more a case of awareness and knowledge of the mountains then about the avalanches themselves.

Not all mountains are at risk of avalanches.  Certain types of environments and conditions are required before an avalanche will form.  

But the best advice that can be given for avoiding avalanches is that KNOWLEDGE IS THE MOST IMPORTANT TOOL. 

DoC ( Department of Conservation) cannot stop you going out into the mountains, but they can advise you. Take notice of their advice as they are familiar with the conditions and the dangers.

Below are some summarised points and useful links to help you on your way.

General tips for avoiding Avalanches

  • Previous Avalanche Activity in the area
  • Stay on slopes less than 30 degrees
  • Carry and know how to use avalanche rescue gear
  • Travel down the edge of the slope rather than the center
  • Be aware of the temperature and snow wetness
  • Hoar frosts and long frosty mornings creates unstable snow layers
  • Avoid travelling under cornices when the snow turns wet
  • Mornings are safer than afternoons. When the day has heated up and the sun has changed the snow, the danger rises
  • Talk to the patrollers. They are out there all of the time and they know the snow
  • Look at the weather charts and look for the Avalanche Advisory board www.avalanche.net
  • Shady slopes versus sunny
  • No other tracks on the slope
  • Ridges and gentle slopes are safer than bowls and gullies. Roll overs stretch the snow while hollows compact the snow and creates pressure points. These are dangerous places to be.

Surface instability Clues

  • Previous Avalanche Activity in the area
  • Collapsing or a sudden drop of the height of the snow pack
  • Shooting cracks visible on the surface of snow pack
  • A hollow sound when walking on hard snow pack
  • Snow still in tree tops 24 hours after storm
  • Recently deposited snow
  • Avalanches are more likely below a cornice than on the edges of a ridge

 

Rescue Tips

  • Localization with an Avalanche Transceiver. A transceiver covers an area the size of a football field.
  • Know avalanche search and rescue grid patterns and search procedures
  • Visible Clues and Avalanche Rescue. Look for gloves, hats, poles a,d skis or snowboards and mark the site. The victim will be below that point.
  • Burial Depth. Each cubic metre weighs a tonne. 4 metres = 4 tonnes of snow on the body.  Its heavy stuff!
  • Tip for self rescue. PRACICE, PRACTICE, PRACTICE.  Know your gear so you can search with speed. Make sure your mates are better than you are. You will want them to be champions if you get caught.

 

Attitudes Not To Have

  • LATE FOR WORK and not taking time to do the essential checks
  • The lion , I am the leader and I know everything.
  • The horse, heading home and thinking of a shower and a warm meal, not thinking about whats happening right now.
  • Putting your life in someone elses hands. They might be dreaming of something else and not about the job in hand. Always keep looking out.

Other Resources

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