Mountain safety - avalanche threat

Being caught in an avalanche is perhaps the greatest fear of all those who undertake off-piste skiing or boarding and ski-touring. The boom in the snow sports industry, high lift-stations, fat skis and snow boards have given access to the mountain to many who do not have the necessary experience to deal with the conditions and to recognise the warning signs. Snow conditions can vary from day to day, and even hour to hour as weather conditions alter the structure of the snow. Knowledge of the snow and understanding of the terrain are necessary for the best form of avalanche safety: that is avalanche avoidance.

The risk of avalanches on the patrolled runs is minimal as ski resorts go to great lengths to protect their pistes - incidents do happen but are thankfully infrequent. However, avalanches and accidents can occur just off the pisted areas. The important point is to be prepared before you venture away from the pistes. An avalanche doesn't need to be of blockbuster movie proportions to be extremely hazardous to your, or others', life.

A useful and daily updated avalanche risk guide for the Courchevel and Three Vallees area is available from Henry's Avalache Talk website. You can also catch Henry live with a report about the day's off piste conditions on Radio Meribel (97.9 Mhz or 98.9 Mhz) between 8am and 10am each morning.

The following information is not to be accepted as a set of instructions, it is designed merely provide guidance for those who wish to go off piste, and facilitating informed decision-making. It is also worth noting that avalanches are not the only dangers of off-piste: natural obstacles such as crevasses, buried rocks or cliffs are also potential hazards. It is highly recommended that you take a mountain guide whilst venturing into unknown territory.

Some avalanche facts:

• In 90% of avalanche incidents involving skiers and snow boarders, the victim or someone in the victim's party triggers the avalanche
• The common avalanches to occur are slab (which account for almost all avalanche fatalities. A cohesive plate of snow slides as a unit on top of weaker snow) or flow (powder) avalanches
• Experience indicates that about 90% of avalanche victims will be recovered alive if they are pulled out within the first 15 minutes. After approximately 45 minutes, the chances of survival drop dramatically to between 30-40%. After 2 hours, the chances of being pulled alive are negligable
• Approximately 50% of victims, partially buried survive if their airways are clear. Of the 50%, only about 5% will suffer from deadly injuries due to the fall. Of the other 50% of victims who die, death will usually be attributed to a late rescue as carbon dioxide builds up in the snow around their mouths and they suffocate
• The effects being caught in an avalanche potentially include having clothing, rucksacks, and other equipment ripped off the victim. Wearing a transceiver anywhere else but properly secured around your body can increase the chances of it being separated from you and therefore rendering it virtually useless.

Avalanche Terrain

Avalanches will most often start on slopes of 30-45 degrees. However, that does not mean that avalanches will not start on slopes as shallow as 25 degrees and as steep as 50 degrees.
Knowing the slope angle is "rule number one" in recognizing avalanche terrain, for once slope angles reach 30 degrees, it is still potential avalanche terrain regardless of all other factors. A clinometer and compass, to establish slope face direction, are important tools for gauging slope aspect.
North-facing slopes are the most likely to avalanche during the middle of winter. South-facing slopes become dangerous in the spring and during sunny days as the sun begins to rise higher in the sky. Leeward slopes – those that face away from the prevailing wind; are dangerous because wind borne snow adds to rapid accumulation of depth; also, the hard, hollow-sounding wind slab may develop there. Windward slopes generally have less snow and benefit from wind compaction.

Avalanche indicative risk or Hazard Rating numbers.
The avalanche risk off piste is classified from 1-5 and is intended to give an overall indication only.

Hazard Rating 1/5 - Low

Stability: The snow pack is generally well bonded and stable
Activity: Triggering is possible only with high additional loads[2] on a few very steep extreme slopes[4]. Only a few small natural[6] avalanches (sluffs) possible

Hazard Rating 2/5 - Moderate

Stability: The snow pack is moderately well bonded on some[1] steep[3] slopes, otherwise generally well bonded.
Activity: Triggering is possible with high additional loads[2], particularly on the steep[3] slopes indicated in the bulletin. Large natural[6] avalanches not likely.

Hazard Rating 3/5 - Considerable

Stability: The snow pack is moderately to weakly bonded on many[1] steep[3] slopes.
Activity: Triggering is possible, sometimes even with low additional loads[2]. The bulletin may indicate many slopes which are particularly affected. In certain conditions, medium and occasionally large sized natural[6] avalanches may occur.

Hazard Rating 4/5 - High

Stability: The snow pack is weakly bonded in most[1] places.
Activity: Triggering is probable even with low additional loads[2] on many steep[3] slopes. In some conditions, frequent medium or large sized natural[6] avalanches are likely.

Hazard Rating 5/5 - Very High

Stability: The snow pack is generally weakly bonded and largely unstable.
Activity: Numerous large natural[6] avalanches are likely, even on moderately steep terrain. Extensive safety measures (closures and evacuation) are necessary. No off-piste or back country skiing or travel should be undertaken.

[1] Generally described in more detail in the avalanche bulletin (e.g. altitude, slope aspect, type of terrain, etc.)
[2] Additional load:-
High - e.g. group of skiers, piste machine, avalanche blasting.
Low - e.g. skier, walker
[3] Steep slopes: slopes with an incline of more than 30 degrees.
[4] Steep extreme slopes: those which are particularly unfavourable in terms of the incline, terrain profile, proximity to ridge, smoothness of underlying ground surface
[5] Aspect: compass bearing directly down the slope
[6] Natural: Without human assistance

Avalanche Survival

There is a lot of controversy about what to do if caught in an avalanche. Some say swim (since a person is about three times denser than moving avalanche debris) and others say roll. The most important thing is to keep the mouth free from snow especially when the snow comes to a stop. Try and get your hands in front of your face to make an air space as you are coming to a stop. An air-pocket is essential to survival.

Avalanche rescue - what to take with you when off piste

For anyone going off marked pistes, (including climbers, skiers, snow boarders, snowshoers and walkers); it is advisable that the following items of equipment are carried at all times:

Avalanche Transceivers (beacons). Digital or analogue, these will send out a signal of where the body is located under the snow and/or assist in detecting the location of buried transceivers

Avalanche Probe. To localise a buried victim, and give exact depth

Snow Shovel. For excavating the victim, quickly (speed is the name of the game)

It is worth reiterating that none of these devices will prevent an avalanche or prevent physical injury from occurring, but will assist in the recovery process.

Before starting the day off piste:

• Take a course in avalanche awareness and practice the techniques learned. Henry's Avalanche Talk is one such way to find out more with regards avalanche safety and Mountain Tracks run several such courses in alpine resorts throughout the winter
• Look at the weather and avalanche forecasts for France / Switzerland, reviewing the degree of local avalanche risk also. Henry's Avalanche Talk produces a translation of current avalanche conditions in English and PisteHors.com is an excellent reference also
• Don’t ignore advice given by local mountain guides or others if advised to ski a certain path, or to keep a specific distance between fellow members in a group
• Plan the route carefully, evaluating all different options and assessing all elements of danger. Look at the timings for each route. Inform others of your route, and when you expect to arrive back
• Attach your transceiver properly to you and DON'T FORGET to turn it on, test the signal is working, and make sure you have all the necessary equipment. (A transceiver is of no use if the user has not been trained in its use, it is turned off, or it is in a rucksack - unless you want just your bag to be recovered.)

Avalanche Transceivers

Avalanche transceivers work by sending / receiving electromagnetic signals on a frequency of 457kHz. There are many transceivers available in the marketplace using either analogue (older) or digital technology. Digital and analogue transceivers are compatible.

Analogue transceivers working in "receive" mode, convert the signals being transmitted by the "sending" transceiver from underneath the snow into sound waves. The receive signal is transmitted as a 'beep' which gets louder and stronger the closer the receiving transceiver gets to the emitting transceiver.

Digital transceivers interpret the same signal. A microprocessor converts the signals into visual data on screen, assisting with more accurate directional information. Digital transceivers are reportedly simpler to use than analogue ones.

Avalanche transceiver equipment tips

• Wear the transceiver as close as possible to your body. A transceiver worn just below the waterproof layer will be exposed if the layer is taken off when climbing and could then be torn off by the force of the avalanche. In addition, body heat will keep the transceiver and batteries warm aiding battery life.
• It has been found that mobile phones interfere with the electromagnetic fields of a transceiver, mobile phones must be turned off at all times or in the very least kept as far away from each other as possible
• Remove and dispose of batteries at the end of the season. Use new batteries at the start of the season, test and change frequently
• Train at the start of and several times during the season, you can practice in your local park or even in the back garden. The stress of an avalanche is not the time to get the instruction book out! The search should almost be reflexive
• Do not put a transceiver in your rucksack as this may be torn off by the force of an avalanche, and will result in only your rucksack being saved by the rescue services
• Probing at right angles on a steep slope reduces the depth of snow to be dug (hypotenuse rule)
• Remember that the transceiver is just a search and rescue device and doesn't enable you to go off-piste in poor conditions
• Beginners often search with analogue devices at too high a volume. The volume should be reduced systematically to reduce the search area
• If not in Europe, make sure that the local frequency is the same as that in use
• Remember an avalanche transceiver is the only device that permits a group to perform their own search and rescue operation in the minimum amount of time.


Some tips when skiing or boarding off piste.

• Ski or board one at a time. If there is a slope that you are nervous about, only one person at a time should go onto the slope. Whether crossing, or going up or down, do so one at a time while all others act as spotters from a safe location. Should an avalanche occur, there will be only one victim and lots of rescuers
• Avoid the centre. The greatest danger on any steep slope comes in the middle of it. Should an avalanche break, there is no escape route. Avoid the centre of open slopes. Cross it at the very top or bottom. Go up it or down along the edges. These positions give a much better chance to escape
• Stay on shallow slopes. Generally, it is possible to travel avalanche-free on slopes up to 25 degrees, and more than 95% of the time it is safe on slopes up to 30 degrees. To measure angles exactly, is it possible to purchase an inexpensive slope meter. However; be extra cautious wherever steeper slopes lie above shallow ones. Though avalanches won't start on shallow slopes, it is possible that an avalanche could be triggered above, placing individuals in harm's way
• Don’t travel alone. Whilst nothing may be as companionable as one's self, there is no greater way to increase an avalanche risk than traveling alone. There is no one to save you from partial or shallow burials.
• Practice, practice, practice your avalanche drill.

 

 

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