avalanche rescue avalanche rescue avalanche rescue involves locating and retrieving people who have been buried in avalanches. united states forest service avalanche danger advisories. prevention avalanche blasting in french ski resort tignes (3,600 m)snow fences in switzerland there are several ways to prevent avalanches and lessen their power and destruction. they are employed in areas where avalanches pose a significant threat to people, such as ski resorts and mountain towns, roads and railways. explosives are used extensively to prevent avalanches, especially at ski resorts where other methods are often impractical. explosive charges are used to trigger small avalanches before enough snow can build up to cause a large avalanche. snow fences and light walls can be used to direct the placement of snow. snow builds up around the fence, especially the side that faces the prevailing winds. downwind of the fence, snow buildup is lessened. this is caused by the loss of snow at the fence that would have been deposited and the pickup of the snow that is already there by the wind, which was depleted of snow at the fence. when there is a sufficient density of trees, they can greatly reduce the strength of avalanches. they hold snow in place and when there is an avalanche, the impact of the snow against the trees slows it down. trees can either be planted or they can be conserved, such as in the building of a ski resort, to reduce the strength of avalanches. artificial barriers can be very effective in reducing avalanche damage. there are several types. one kind of barrier (snow net) uses a net strung between poles that are anchored by guy wires in addition to their foundations. these barriers are similar to those used for rockslides. another type of barrier is a rigid fence like structure (snow fence) and may be constructed of steel, wood or pre-stressed concrete. they usually have gaps between the beams and are built perpendicular to the slope, with reinforcing beams on the downhill side. rigid barriers are often considered unsightly, especially when many rows must be built. they are also expensive and vulnerable to damage from falling rocks in the warmer months. finally, there are barriers that stop or deflect avalanches with their weight and strength. these barriers are made of concrete, rocks or earth. they are usually placed right above the structure, road or railway that they are trying to protect, although they can also be used to channel avalanches into other barriers. occasionally, earth mounds are placed in the avalanche's path to slow it down. safety in avalanche terrain terrain management - terrain management involves reducing the exposure of an individual to the risks of travelling in avalanche terrain by carefully selecting what areas of slopes to travel on. features to be cognizant of include not undercutting slopes (removing the physical support of the snow pack), not travelling over convex rolls (areas where the snow pack is under tension), staying away from weaknesses like exposed rock, and avoiding areas of slopes that expose one to terrain traps (gulleys that can be filled in, cliffs over which one can be swept, or heavy timber into which one can be carried). group management - group management is the practice of reducing the risk of having a member of a group, or from the avalanche hazard before the next one leaves protective cover. route selection should also consider what dangers lie above and below the route, and the consequences of an unexpected avalanche (i.e., unlikely to occur, but deadly if it does). stop or camp only in safe locations. wear warm gear to delay hypothermia if buried. plan escape routes. in determining the size of the group balance the hazard of not having enough people to effectively carry out a rescue with the risk of having too many members of the group to safely manage the risks. it is generally recommended not to travel alone, because there will be no-one to witness your burial and start the rescue. additionally, avalanche risk increases with use; that is, the more a slope is disturbed by skiers, the more likely it is that an avalanche will occur. most important of all practise good communication within a group including clearly communicating the decisions about safe locations, escape routes, and slope choices, and having a clear understanding of every members skills in snow travel, avalanche rescue, and route finding. risk factor awareness - risk factor awareness in avalanche safety requires gathering and accounting for a wide range of information such as the meteorological history of the area, the current weather and snow conditions, and equally important the social and physical indicators of the group. leadership - leadership in avalanche terrain requires well defined decision making protocols that use the observed risk factors. these decision making frameworks are taught in a variety of courses provided by national avalanche resource centres in europe and north america. fundamental to leadership in avalanche terrain is honestly assessing and estimating the information that was ignored or overlooked. recent research has shown that there are strong psychological and group dynamic determinants that lead to avalanche involvement. to quickly find and rescue a person buried in an avalanche, a probe, beacon, and shovel are essential. the buried person must also be wearing an avalanche beacon. even small avalanches are a serious danger to life, even with properly trained and equipped companions who avoid the avalanche. between 55 and 65 percent of victims buried in the open are killed, and only 80 percent of the victims remaining on the surface survive. (mcclung, p.177). research carried out in switzerland based on 422 buried skiers indicates how the chances of survival drop: very rapidly from 92 percent within 15 minutes to only 30 percent after 35 minutes (victims die of suffocation) near zero after two hours (victims die of injuries or hypothermia) (historically, the chances of survival were estimated at 85% within 15 minutes, 50% within 30 minutes, 20% within one hour). consequently, it is vital that everyone surviving an avalanche is used in an immediate search and rescue operation, rather than waiting for help to arrive. additional help can be called once it can be determined if anyone is seriously injured or still remains unaccounted for after the immediate search (i.e., after at least 30 minutes of searching). even in a well equipped country such as france, it typically takes 45 minutes for a helicopter rescue team to arrive, by which time most of the victims are likely to have died. in some cases avalanche victims are not located until spring thaw melts the snow, or even years later when objects emerge from a glacier. search and rescue equipment a blackhawk helicopter as the crew prepares to evacuate tourists stranded by an avalanche in galtür, austria, on february 25, 1999. chances of a buried victim being found alive and rescued are increased when everyone in a group is carrying and using standard avalanche equipment, and have trained in how to use it. a beacon, shovel and probe is considered the minimum equipment to carry for companion rescue. organized rescue involves ski patrols and mountain rescue teams who are often equipped with other technologies to search for buried victims. rescue equipment can make a difference, and in 2010 the french national association for the study of snow and avalanches (anena) recommended that all off-piste skiers should carry beacons, probes, shovels, and recco reflectors. avalanche cords the use of avalanche cords goes back to the early 20th century and a bavarian mountaineer named eugen oertel. in the united states the concept was recommended as early as 1908 in the colorado newspaper - the ouray herald (november 13) - when the editor repeated the suggestion that miners in the san juan mountains adopt "snowslide ribbons" to safeguard their travels to and from the mines. the principle is simple. an approximately 15 metre long red cord (similar to parachute cord) is attached to the belt of the person to be protected. while they are skiing, snowboarding, or walking, the cord is dragged along behind them. the intent is, that if the person gets buried in an avalanche, the light cord stays on top of the snow. due to the colour the cord would be easily visible for companions. commercial avalanche cords have metal markings every one to three metres indicating the direction and length to the victim. avalanche cords were popular before beacons became available, and while cords were thought to be effective markers there was never any proof of their effectiveness. in the 1970s melchior schild of the swiss federal institute for snow and avalanche research (slf) reviewed 30 years of swiss avalanche accidents and rescues from 1944/45 to 1973/74. of the 2042 avalanche victims he found only seven cases where avalanche cords were used (not including the 2 mentioned above). in five cases part of the cord was visible on the surface but so too was part of a victim. in the sixth case the victim was completely buried, but part of the cord was visible; this victim died of trauma. in the seventh case the completely buried avalanche cord was located by an avalanche rescue dog, however, the cord had become detached from the victim, and her body was found much later. in knox williams' and betsy armstrong's 1986 ‘’the avalanche book’’, they cite an early 1970s study, in which avalanche cords were tested on sandbag dummies. the dummies were placed onto steep slopes where explosives were used to trigger avalanches. trials showed a portion of the cord remained on the surface only 40% of the time. the other 60% of the time the cord was completely buried along with the dummy. typically the cord had spooled around the dummy. in 1975, at a symposium of avalanche rescue experts hosted by the international foundation vanni eigenmann, schild concluded, “on the basis of these results the avalanche cord can no longer be considered reliable.” in the united states there have been two accidents with five buried victims, all wearing avalanche cords. in one accident, an avalanche cord remained on the surface. in the second accident five ski mountaineers with cords deployed triggered an avalanche. one skier was partly buried, but his four friends and cords were completely buried. moderate snow and the loss of the survivor's eyeglasses only worsened the situation. the search was called off a few days later. the four were eventually found many months later after their bodies with attached cords melted out of the snow. on one victim the cord was wrapped tightly around the body. avalanche cords are now regarded obsolete, as beacons are available and much more effective. beacons avalanche transceivers — known as beacons, "beepers", peeps (pieps), arvas (appareil de recherche de victimes en avalanche, in french), lvs (lawinen-verschütteten-suchgerät, swiss german), or various other trade names, are important for every member of the party. they emit a "beep" via 457 khz radio signal in normal use, but may be switched to receive mode to locate a buried victim up to 80 meters away. analog receivers provide audible beeps that rescuers interpret to estimate distance to a victim. to use the receiver effectively requires regular practice. some older models of beepers operated on a different frequency (2.275 khz ) and a group leader should ensure these are no longer in use. since about 2000 nearly all avalanche rescue transceivers use digital displays to give visual indications of direction and distance to victims. most users find these beacons easier to use, but to be effective still requires considerable practice by the user. beacons are the primary rescue tool for companion rescue and are considered active devices because the user must learn to use and care for their device. avalanche transceivers are not to be confused with several smartphone applications calling themselves smartphone avalanche search apps using two-way communication technologies. every member of the party must be equipped with an avalanche transceiver. probes avalanche security, search and rescue equipment (left to right): avalanche airbag system, collapsed probe, shovel, avalanche transceiver portable (collapsible) probes can be extended to probe into the snow to locate the exact location of a victim at several yards / metres in depth. when multiple victims are buried, probes should be used to decide the order of rescue,