A Himalayan avalanche near Mount Everest. Mount Everest, also called Sagarmatha (सगरमाथा meaning Head of the Sky) or Chomolungma, Qomolangma or Zhumulangma (in
The toe of an avalanche in Alaska's Kenai Fjords. Alaska ( Аляска Alyaska) is a state in the United States of America, in the northwest of the North American continent Established in 1980 by the Alaska National Interest Lands Conservation Act, Kenai Fjords National Park is a United States National Park on the Kenai
The beginning of a loose snow avalanche. A loose snow avalanche is an Avalanche formed in Snow with little internal Cohesion among individual Snow crystals.
This article refers to the natural event. For other uses, see Avalanche (disambiguation)

An avalanche is an abrupt and rapid flow of snow, often mixed with air and water, down a mountainside. Avalanches are among the biggest dangers in the mountains for both life and property. A mountain is a Landform that extends above the surrounding Terrain in a limited area with a peak

## Types

Several types of snow avalanche may occur. Loose snow avalanches occur when the weight of the snowpack exceeds the shear strength within it, and are most common on steeper terrain. A loose snow avalanche is an Avalanche formed in Snow with little internal Cohesion among individual Snow crystals. "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. Shear strength in Engineering is a term used to describe the strength of a material or component against the type of yield or Structural failure where the In fresh, loose snow the release is usually at a point and the avalanche then gradually widens down the slope as more snow is entrained, usually forming a teardrop appearance. This is in contrast to a slab avalanche. Slab avalanches account for around 90% of avalanche-related fatalities, and occur when there is a strong, stiff layer of snow known as a slab. These are usually formed when snow is deposited by the wind on a lee slope. When the slab fails, the fracture, in a weak layer, very rapidly propagates so that a large area, that can be hundreds of metres in extent and several metres thick, starts moving almost instantaneously. The third starting type is a slush avalanche which occurs when the snowpack becomes saturated by water. These tend to also start and spread out from a point.

As avalanches move down the slope they may entrain snow from the snowpack and grow in size. The snow may also mix with the air and form a powder cloud. An avalanche with a powder cloud is known as a powder snow avalanche. The powder cloud is a turbulent suspension of snow particles that flows as a gravity current. In Fluid dynamics, a gravity current is a primarily horizontal flow in a gravitational field that is driven by a Density difference Powder snow avalanches are the largest avalanches and can exceed 300 km/h and 10,000,000 tonnes of snow, they can flow for long distance along flat valley bottoms and even up hill for short distances.

### Contributing factors

All avalanches are caused by an over-burden of material, typically snowpack, that is too massive and unstable for the slope that supports it. "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. Determining the critical load, the amount of over-burden which is likely to cause an avalanche, is a complex task involving the evaluation of a number of factors.

Terrain Slopes flatter than 25 degrees or steeper than 60 degrees typically have a low risk of avalanche. Snow does not accumulate significantly on steep slopes; also, snow does not flow easily on flat slopes. Human triggered avalanches have the greatest incidence when the snow's angle of repose is between 35 and 45 degrees; the critical angle, the angle at which the human incidence of avalanches is greatest, is 38 degrees. The angle of repose is an Engineering property of Granular materials The angle of repose is the maximum angle of a stable slope determined by friction cohesion The rule of thumb is: A slope that is flat enough to hold snow but steep enough to ski has the potential to generate an avalanche, regardless of the angle. 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. Snow skiing is a group of sports utilizing Skis as primary equipment [1]

The four variables that influence snowpack evolution and composition are temperature, precipitation, solar radiation, and wind. "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. In the mid-latitudes of the Northern Hemisphere, more avalanches occur on shady slopes with northern and north-eastern exposures. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' However, when the human triggered incidence of avalanches are normalized to mid-latitude rates of recreational use, no significant difference in hazard for a given exposure direction can be found. [2] The snowpack on slopes with southern exposures are strongly influenced by sunshine; daily cycles of surface thawing and refreezing create a crust that may tend to stabilize an otherwise unstable snowpack, but the crust, once it has been fractured, may detach itself from the underlying layers of snow, slide, and promote the generation of an avalanche. Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. Slopes in the lee of a ridge or other wind obstacle accumulate more snow and are more likely to include pockets of abnormally deep snow, windslabs, and cornices, all of which, when disturbed, may trigger an avalanche. In climbing a cornice is an overhanging edge of Snow on a ridge or the crest of a mountain which are built up by drifting snow

Convex slopes are more dangerous than concave slopes. In Mathematics, a real-valued function f defined on an interval (or on any Convex subset of some Vector space) is called convex In Mathematics, a concave function is the negative of a Convex function. The primary factor contributing to the increased avalanche danger on convex slopes is a disparity between the tensile strength of snow layers and their compressive strength. Tensile strength \sigma_{UTS} or S_U is the Stress at which a material breaks or permanently deforms Compressive strength is the capacity of a Material to withstand axially directed pushing forces

Another factor affecting the incidence of avalanches is the nature of the ground surface underneath the snow cover. Full-depth avalanches (avalanches that sweep a slope virtually clean of snow cover) are more common on slopes with smooth ground cover, such as grass or rock slabs. Vegetation plays an important role in anchoring a snowpack; however, in certain instances, boulders or vegetation may actually create weak areas deep within the snowpack.

#### Snow structure and characteristics

The structure of the snowpack is a strong predictor of avalanche danger. For an avalanche to occur, it is necessary that a snowpack have a weak layer (or instability) below the surface and an overlying slab of snow. Unfortunately, the relationship between easily-observed properties of snow layers (strength, grain size, grain type, temperature, etc. ) and avalanche danger are extraordinarily complex; consequently, this is an area that is not yet fully understood. Furthermore, snow cover and stability often vary widely within relatively small areas, and a risk assessment of a given slope is unlikely to remain valid, accurate, or useful for very long.

Various snow composition and deposition characteristics also influence the likelihood of an avalanche. Newly-fallen snow requires time to bond with the snow layers beneath it, especially if the new snow is light and powdery. Snow that lies above boulders or certain types of plants has little to help anchor it to the slope. Larger snow crystals, generally speaking, are less likely to bond together to form strong structures than smaller crystals are. Consolidated snow is less likely to slough than light powdery layers; however, well-consolidated snow is more likely to generate unstable slabs.

#### Weather

Weather also influences the evolution of snowpack formation. The most important factors are heating by the sun, radiational cooling, vertical temperature gradients in standing snow, snowfall amounts, and snow types. Radiational cooling is the cooling of the Earth's surface through Thermal radiation in the Infrared frequency In atmospheric sciences ( Meteorology, Climatology and related fields the temperature gradient (typically of air, more generally of any Fluid

If the temperature is high enough for gentle freeze-thaw cycles to take place, the melting and refreezing of water in the snow strengthens the snowpack during the freezing phase and weakens it during the thawing phase. A rapid rise in temperature, to a point significantly above the freezing point, may cause a slope to avalanche, especially in spring. Persistent cold temperatures prevent the snow from stabilizing; long cold spells may contribute to the formation of depth hoar, a condition where there is a pronounced temperature gradient, from top to bottom, within the snow. Depth hoares are large Crystals occurring at the base of a Snowpack that form from when uprising water Vapor freezes onto existing snow crystal When the temperature gradient becomes sufficiently strong, thin layers of "faceted grains" may form above or below embedded crusts, allowing slippage to occur.

Snowstorms and rainstorms are important contributors to avalanche danger. Heavy snowfall may cause instability in the existing snowpack, both because of the additional weight and because the new snow has insufficient time to bond to underlying snow layers. Rain has a similar effect. In the short-term, rain causes instability because, like a heavy snowfall, it imposes an additional load on the snowpack; and, once rainwater seeps down through the snow, it acts as a lubricant, reducing the natural friction between snow layers that holds the snowpack together. Most avalanches happen during or soon after a storm.

Daytime exposure to sunlight can rapidly destabilize the upper layers of a snowpack. Sunlight reduces the sintering, or necking, between snow grains. Sintering is a method for making objects from powder, by heating the material (below its Melting point - solid state sintering until its particles adhere In materials or mechanical engineering necking is a mode of Ductile flow of a material in tension. During clear nights, the snowpack can strengthen, or tighten, through the process of long-wave radiative cooling. When the night air is significantly cooler than the snowpack, the heat stored in the snow is re-radiated into the atmosphere.

## Dynamics

When an avalanche occurs, as the snow slides down the slope any slab present begins to fragment into increasingly smaller tumbling fragments. If the fragments become small enough the avalanche takes on the characteristics of a fluid. FLUID ( F ast L ight '''U'''ser '''I'''nterface D esigner is a graphical editor that is used to produce FLTK Source code When sufficiently fine particles are present they can become airborne and, given a sufficient quantity of airborne snow, this portion of the avalanche can become separated from the bulk of the avalanche and travel a greater distance as a powder snow avalanche. [3] Scientific studies using radar, following the 1999 Galtür avalanche disaster, confirmed suspicions that a saltation layer forms between the surface and the airborne components of an avalanche, which can also separate from the bulk of the avalanche. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships On February 23 1999 the worst Alpine avalanche in 40 years It killed 31 people in the small Alpine village of Galtür, Austria. For definition and other use disambiguation see Saltation In Geology, saltation (from Latin, saltus, "leap" [4]

Driving a (non-airborne) avalanche is the component of the avalanche's weight parallel to the slope; as the avalanche progresses any unstable snow in its path will tend to become incorporated, so increasing the overall weight. This force will increase as the steepness of the slope increases, and diminish as the slope flattens. Resisting this are a number of components that are thought to interact with each other: the friction between the avalanche and the surface beneath; friction between the air and snow within the fluid; fluid-dynamic drag at the leading edge of the avalanche; shear resistance between the avalanche and the air through which it is passing, and shear resistance between the fragments within the avalanche itself. An avalanche will continue to accelerate until the resistance exceeds the forward force. [5]

### Modelling

Attempts to model avalanche behaviour date from the early 20th century, notably the work of Professor Lagotala in preparation for the 1924 Winter Olympics in Chamonix. The 1924 Winter Olympics, officially known as the I Olympic Winter Games, were a Winter Multi-sport event which was held in 1924 in Chamonix Chamonix-Mont-Blanc or more commonly Chamonix (ʃamɔni in French is a Town and commune in eastern France, in the Haute-Savoie [6] His method was developed by A. Voellmy and popularised following the publication in 1955 of his Ober die Zerstorunskraft von Lawinen (On the Destructive Force of Avalanches). [7]

Voellmy used a simple empirical formula based on Bernoulli's principle, treating an avalanche as a sliding block of snow moving with a force that was proportional to the square of the speed of its flow:[8]

$Pref={1 \over 2} { \rho} { v^2}$

He and others subsequently derived other formulae that take other factors into account, with the Voellmy-Salm-Gubler and the Perla-Cheng-McClung models becoming most widely used as simple tools to model flowing (as opposed to airborne) avalanches. In Fluid dynamics, Bernoulli's principle states that for an Inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in [6]

Since the 1990s many more sophisticated models have been developed. In Europe much of the recent work was carried out as part of the SATSIE (Avalanche Studies and Model Validation in Europe) research project supported by the European Commission[9] which produced the leading-edge MN2L model, now in use with the Service Réstitution Terrains en Montagne (Mountain Rescue Service) in France, and D2FRAM (Dynamical Two-Flow-Regime Avalanche Model), which was still undergoing validation as of 2007. The European Commission (formally the Commission of the European Communities) is the executive branch of the European Union. [10]

## Avalanche avoidance

United States Forest Service avalanche danger advisories.

Due to the complexity of the subject, winter travelling in the backcountry (off-piste) is never 100% safe. Backcountry skiing is Skiing in a sparsely inhabited Rural region over ungroomed and unmarked slopes or Pistes More importantly the land and the snow pack Good avalanche safety is a continuous process, including route selection and examination of the snowpack, weather conditions, and human factors. Several well-known good habits can also minimize the risk. If local authorities issue avalanche risk reports, they should be considered and all warnings heeded. Never follow in the tracks of others without your own evaluations; snow conditions are almost certain to have changed since they were made. Observe the terrain and note obvious avalanche paths where vegetation is missing or damaged, where there are few surface anchors, and below cornices or ice formations. Avoid traveling below others who might trigger an avalanche.

### Prevention

Snow fences in Switzerland
Avalanche blasting in French ski resort Tignes (3,600 m)
Main article: Avalanche control

There are several ways to prevent avalanches and lessen their power and destruction. Avalanche control or avalanche defense activities aim at the elimination and reduction of hazard and damage resulting from Avalanches There are two major groups They are employed in areas where avalanches pose a significant threat to people, such as ski resorts and mountain towns, roads and railways. A ski area is a developed recreational facility usually on a Mountain or large Hill, containing ski trails and vital supporting services Explosives are used extensively to prevent avalanches, especially at ski resorts where other methods are often impractical. An explosive material is a material that either is chemically or otherwise Energetically unstable or produces a sudden expansion of the material usually accompanied 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. A snow fence is a structure used to force drifting of Snow to occur in a predictable place rather than in a more natural method Snow builds up around the fence, especially the side that faces the prevailing winds. Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) 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. A tree is a perennial Woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or 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. Avalanche nets ( snow avalanche protection nets, snow nets) are flexible Snow supporting structures for Avalanche control, constructed of A guy-wire or guy-rope is a tensioned cable designed to add stability to structures (frequently ship masts, radio masts, Wind turbines, These barriers are similar to those used for rockslides. A landslide is a geological phenomenon which includes a wide range of ground movement such as rock falls deep failure of slopes and shallow debris flows which can occur Another type of barrier is a rigid fence like structure (snow fence) and may be constructed of steel, wood or pre-stressed concrete. A snow fence is a structure used to force drifting of Snow to occur in a predictable place rather than in a more natural method Steel is an Alloy consisting mostly of Iron, with a Carbon content between 0 Wood is hard fibrous lignified structural tissue produced as secondary Xylem in the stems of Woody plants notably trees but also shrubs Concrete is a construction material composed of Cement (commonly Portland cement) as well as other cementitious materials such as Fly ash and Slag 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 out 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. A mound is a general term for an artificial heaped Pile of Earth, Gravel, Sand, rocks

### Safety in avalanche terrain

• Terrain management - Terrain management involves reducing the exposure of an individual to the risks of traveling in avalanche terrain by carefully selecting what areas of slopes to travel on. Features to be cognizant of include not under cutting slopes (removing the physical support of the snow pack), not traveling 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 a whole group involved in an avalanche. Minimize the number of people on the slope, and maintain separation. Ideally one person should pass over the slope into an area protected 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. Most important of all practice good communication with in 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.
• Group size - Group size must 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. There will be no-one to witness your burial and start the rescue.
• Leadership - Leadership in avalanche terrain requires well defined decision making protocols, which are being taught in a growing number of courses provided by national avalanche resource centers in Europe and North America. Fundamental to leadership in avalanche terrain is an honest attempt at assessing ones blind spots (what information am I ignoring?) There is a growing body of research into the psychological behaviors and group dynamics that lead to avalanche involvement.

## Human survival and avalanche rescue

Avalanche on the backside (east) of Mount Timpanogos, Utah at Aspen Grove trail

Even small avalanches are a serious danger to life, even with properly trained and equipped companions who avoid the avalanche. Mount Timpanogos is the second highest Mountain in Utah 's Wasatch Range (second to Mount Nebo) The State of Utah (ˈjuːtɔː or) is a western state of the United States. 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 Italy[11] 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% percent within 15 minutes, 50% within 30 minutes, 20% within one hour). Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest Snow skiing is a group of sports utilizing Skis as primary equipment Treatment of physical trauma is described here and in First aid. Hypothermia is a condition in which an organism's temperature drops below that required for normal Metabolism and bodily functions

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 unaccountable 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. This article is about the country For a topic outline on this subject see List of basic France topics.

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. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout Galtür is a village and Ski resort in the upper Paznaun valley in Tyrol ( Austria) Austria (Österreich ( officially the Republic of Austria (Republik Österreich Events 138 - The Emperor Hadrian adopts Antoninus Pius, effectively making him his successor Year 1999 ( MCMXCIX) was a Common year starting on Friday (link will display full 1999 Gregorian calendar)

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. However, like a seat belt in a vehicle, using the right equipment does not justify exposing yourself to unnecessary risks with the hope that the equipment might save your life when it is needed. A beacon, shovel and probe is considered the minimum equipment to carry when exposing yourself to avalanche danger.

#### Avalanche cords

Using an avalanche cord is the oldest form of equipment — mainly used before beacons became available. The principle is simple. An approximately 10 meter long red cord (similar to parachute cord) is attached to the person in question's belt. While skiing, snowboarding, or walking the cord is dragged along behind the person. If the person gets buried in an avalanche, the light cord stays on top of the snow. Due to the color the cord is easily visible for rescue personnel. Typically the cord has iron markings every one meter that indicate the direction and length to the victim.

#### Beacons

Main article: Avalanche transceiver

Beacons — known as "beepers", peeps (pieps), ARVAs (Appareil de Recherche de Victimes en Avalanche, in French), LVS (Lawinen-Verschütteten-Suchgerät, Swiss German), avalanche transceivers, or various other trade names, are important for every member of the party. Avalanche transceivers are a class of radio transceivers specialized to the purpose of finding people or equipment buried under Snow. A transceiver is a device that has both a Transmitter and a receiver which are combined and share common circuitry or a single housing 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.

Recent digital models also attempt to give visual indications of direction and distance to victims and require less practice to be useful. There are also passive transponder devices that can be inserted into equipment, but they require specialized search equipment that might only be found near an organized sports area.

#### Probes

Portable probe, collapsed

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, with the shallowest being dug out first since they have the greatest chance of survival.

Probing can be a very time-consuming process if a thorough search is undertaken for a victim without a beacon. In the U. S. , 86% of the 140 victims found (since 1950) by probing were already dead. [3] Survival/rescue more than 2 m deep is relatively rare (about 4%). Probes should be used immediately after a visual search for surface clues, in coordination with the beacon search.

#### Shovels

When an avalanche stops, the deceleration normally compresses the snow to a hard mass. Shovels are essential for digging through the snow to the victim, as the deposit is often too dense to dig with hands or skis. A large scoop and sturdy handle are important. Shovels are also useful for digging snow pits as part of evaluating the snow pack for hidden hazards, such as weak layers supporting large loads.

#### Avalung

Recently, a device called an Avalung has been introduced for use in avalanche terrain. The device consists of a mouth piece and a bag that either sits on one's chest or in a fitted backpack. During an avalanche victims usually suffer from suffocation as the snow around them melts from the warm condesation of the victims breath and then freezes, disallowing oxygen to flow to the victim. The Avalung prevents this by drawing breath over a large surface area and pushing the warm exhaled air to a different location than where the air is being inhaled.

#### Other devices

More back-country adventurers are also carrying Emergency Position-Indicating Radio Beacon (EPIRB) or Personal Locating Beacons (PLBs) containing the Global Positioning System (GPS). In the field of Search and Rescue (SAR distress radio beacons, also collectively known as distress beacons, emergency beacons, or simply beacons Basic concept of GPS operation A GPS receiver calculates its position by carefully timing the signals sent by the constellation of GPS Satellites high above the Earth This device can quickly notify search and rescue of an emergency and the general location (within 100 yards), but only if the person with the EPIRB has survived the avalanche and can activate the device. Alternatively, survivors may use a mobile phone to notify emergency personnel of their location obtained from a GPS without EPIRB capability.

Technology to summon outside help is to be used with the knowledge that those responding will likely be performing a body recovery. Only on-site rescuers are in position to render assistance during the brief interval that the victim is most likely to survive.

Other rescue devices are proposed, developed and used, such as avalanche balls, vests and airbags, based on statistics that most deaths are due to suffocation.

Although inefficient, some rescue equipment can be improvised by unprepared parties: ski poles can become short probes, skis or snowboards can be used as shovels. A first aid kit and equipment is useful for assisting survivors who may have cuts, broken bones, or other injuries, in addition to hypothermia. Wilderness first aid is the specific discipline of First aid which relates to care in remote areas where Emergency medical services will be difficult to obtain or Hypothermia is a condition in which an organism's temperature drops below that required for normal Metabolism and bodily functions

### Witnesses as rescuers

Periodic winter avalanches on this 800 m high slope transport woody debris to the flat in the foreground.

Survival time is short, if a victim is buried. There is no time to waste before starting a search, and many people have died because the surviving witnesses failed to do even the simplest search.

Witnesses to an avalanche that engulfs people are frequently limited to those in the party involved in the avalanche. Those not caught should try to note the locations where the avalanched person or people were seen. This is such an important priority it should be discussed before initially entering an avalanche area. Once the avalanche has stopped, and there is no danger of secondary slides, these points should be marked with objects for reference. Survivors should then be counted to see who may be lost. If the area is safe to enter, a visual search of the likely burial areas should begin (along a downslope trajectory from the marked points last seen). Some victims are buried partially or shallowly and can be located quickly by making a visual scan of the avalanche debris and pulling out any clothing or equipment found. It may be attached to someone buried.

Alert others if a radio is available, especially if help is nearby, but do NOT waste valuable resources by sending a searcher for help at this point. Switch transceivers to receive mode and check them. Select likely burial areas and search them, listening for beeps (or voices), expanding to other areas of the avalanche, always looking and listening for other clues (movement, equipment, body parts). Probe randomly in probable burial areas. Mark any points where signal was received or equipment found. Only after the first 15 minutes of searching should consideration be given to sending someone for help. Continue scanning and probing near marked clues and other likely burial areas. After 30-60 minutes, consider sending a searcher to get more help, as it is more likely than not that any remaining victims have not survived.

Line probes are arranged in most likely burial areas and marked as searched. Continue searching and probing the area until it is no longer feasible or reasonable to continue. Avoid contaminating the scent of the avalanche area with urine, food, spit, blood, etc, in case search dogs arrive.

The areas where buried victims are most likely to be found are: below the marked point last seen, along the line of flow of the avalanche, around trees and rocks or other obstacles, near the bottom runout of the debris, along edges of the avalanche track, and in low spots where the snow may collect (gullies, crevasses, creeks, ditches along roads, etc). Although less likely, other areas should not be ignored if initial searches are not fruitful.

Once a buried victim is found and his or her head is freed, perform first aid (airway, breathing, circulation/pulse, arterial bleeding, spinal injuries, fractures, shock, hypothermia, internal injuries, etc), according to local law and custom. Wilderness first aid is the specific discipline of First aid which relates to care in remote areas where Emergency medical services will be difficult to obtain or

### Victims

Victims caught in an avalanche are advised to try to ski or board toward the side of the avalanche until they fall, then to jettison their equipment and attempt swimming motions. As the snow comes to rest an attempt should be made to preserve an air-space in front of the mouth, and try to thrust an arm, leg or object above the surface, assuming you are still conscious. If it is possible to move once the snow stops, enlarge the air space, but minimize movement to reduce your oxygen consumption. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the

An avalanche by Philipp Jakob Loutherbourg, 1803.

Myth: Avalanches can be triggered by shouting - Avalanches cannot be triggered by sound as the forces exerted by the pressures in sound waves are far too low. The very large shockwaves produced by explosions can trigger avalanches, however, if they are close enough to the surface. [12]

Myth: Spitting while covered in snow can determine the direction upwards - Spitting while covered in snow is not possible because when the snow has settled it becomes very solid and most of the time, moving is not possible. [13]

## Notable avalanches

A large avalanche in Montroc, France, in 1999, 300,000 cubic metres of snow slid on a 30 degree slope, achieving a speed of 100 km/h (60 mph). Montroc is a town in eastern France, located in the territory of the commune of Chamonix. It killed 12 people in their chalets under 100,000 tons of snow, 5 meters (15 ft) deep. The mayor of Chamonix was convicted of second-degree murder for not evacuating the area, but received a suspended sentence. Chamonix-Mont-Blanc or more commonly Chamonix (ʃamɔni in French is a Town and commune in eastern France, in the Haute-Savoie [14]

The small Austrian village of Galtür was hit by the Galtür avalanche in 1999. Galtür is a village and Ski resort in the upper Paznaun valley in Tyrol ( Austria) On February 23 1999 the worst Alpine avalanche in 40 years It killed 31 people in the small Alpine village of Galtür, Austria. The village was thought to be in a safe zone but the avalanche was exceptionally large and flowed into the village. Thirty-one people died.

On May 31, 1970 the Ancash earthquake caused a large avalanche from Huascaran, resulting in the destruction of the town of Yungay, Peru and the death of at least 18,000 people. The 1970 Ancash earthquake or Great Peruvian Earthquake was an undersea Earthquake that occurred on May 31 of that year Huascarán or Nevado Huascarán is a Mountain in the province of Yungay - Cordillera Blanca, part of the Western Andes. Yungay is a town in the Ancash Region in north central Peru, South America. Peru (Perú Piruw Piruw officially the Republic of Peru ( reˈpuβlika del peˈɾu is a country in western South America.

In the northern hemisphere winter of 1951-1952 approximately 649 avalanches were recorded in a three month period throughout the Alps in Austria, France, Switzerland, Italy and Germany. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' Austria (Österreich ( officially the Republic of Austria (Republik Österreich This article is about the country For a topic outline on this subject see List of basic France topics. Switzerland (English pronunciation; Schweiz Swiss German: Schwyz or Schwiiz Suisse Svizzera Svizra officially the Swiss Confederation Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest Germany, officially the Federal Republic of Germany ( ˈbʊndəsʁepuˌbliːk ˈdɔʏtʃlant is a Country in Central Europe. This series of avalanches killed around 265 humans and was termed the Winter of Terror. Winter of Terror is a term used to describe the three month period during the winter of 1950-1951 when a previously unrecorded number of avalanches took place in the Alps

During World War I, approximately 50,000 soldiers died as a result of avalanches during the mountain campaign in the Alps at the Austrian-Italian front, many of which were caused by artillery fire. World War I (abbreviated WWI; also known as the First World War, the Great War, and the War to End All Austria (Österreich ( officially the Republic of Austria (Republik Österreich Italy (Italia officially the Italian Republic, (Repubblica Italiana is located on the Italian Peninsula in Southern Europe, and on the two largest Artillery (from French artillerie) is a military Combat Arm which employs any apparātus machine [15] However, it is very doubtful avalanches were used deliberately at the strategic level as weapons; more likely they were simply a side effect to shelling enemy troops, occasionally adding to the toll taken by the artillery. Avalanche prediction is nearly impossible; forecasters can only assert the conditions, terrain and relative likelihood of slides with the help of detailed weather reports and from localized snowpack observation. "Snowfall" redirects here For other uses see Snow (disambiguation or Snowfall (disambiguation. It would be almost impossible to predict avalanche conditions many miles behind enemy lines, making it impossible to intentionally target a slope at risk for avalanches. Also, high priority targets received continual shelling and would be unable to build up enough unstable snow to form devastating avalanches, effectively imitating the avalanche prevention programs at ski resorts. A ski area is a developed recreational facility usually on a Mountain or large Hill, containing ski trails and vital supporting services

## European avalanche risk table

In Europe, the avalanche risk is widely rated on the following scale, which was adopted in April 1993 to replace the earlier non-standard national schemes. Descriptions were last updated in May 2003 to enhance uniformity. [4]

In France, most avalanche deaths occur at risk levels 3 and 4. In Switzerland most occur at levels 2 and 3. It is thought that this may be due to national differences of interpretation when assessing the risks. [16]

Risk LevelSnow StabilityFlagAvalanche Risk
1 - LowSnow is generally very stable. Avalanches are unlikely except when heavy loads [2] are applied on a very few extreme steep slopes. Any spontaneous avalanches will be minor (sluffs). In general, safe conditions.
2 - LimitedOn some steep slopes the snow is only moderately stable [1]. Elsewhere it is very stable. Avalanches may be triggered when heavy [2] loads are applied, especially on a few generally identified steep slopes. Large spontaneous avalanches are not expected.
3 - MediumOn many steep slopes [1] the snow is only moderately or weakly stable. Avalanches may be triggered on many slopes even if only light loads [2] are applied. On some slopes, medium or even fairly large spontaneous avalanches may occur.
4 - HighOn most steep slopes [1] the snow is not very stable. Avalanches are likely to be triggered on many slopes even if only light loads [2] are applied. In some places, many medium or sometimes large spontaneous avalanches are likely.
5 - Very HighThe snow is generally unstable. Even on gentle slopes, many large spontaneous avalanches are likely to occur.

[1] Stability:

• Generally described in more detail in the avalanche bulletin (regarding the altitude, aspect, type of terrain etc. )

• heavy: two or more skiers or boarders without spacing between them, a single hiker or climber, a grooming machine, avalanche blasting. The word 'hiking' is understood in all English-speaking countries but there are differences in usage UserStan Shebs for a timetable --> Climbing is the activity of using one's hands and feet (or
• light: a single skier or snowboarder smoothly linking turns and without falling, a group of skiers or snowboarders with a minimum 10 m gap between each person, a single person on snowshoes. Development of snowshoes Origins Before humanity built snowshoes nature provided examples

• gentle slopes: with an incline below about 30°.
• steep slopes: with an incline over 30°.
• very steep slopes: with an incline over 35°.
• extremely steep slopes: extreme in terms of the incline (over 40°), the terrain profile, proximity of the ridge, smoothness of underlying ground.

## European avalanche size table

Avalanche size:

SizeRunoutPotential DamagePhysical Size
1 - SluffSmall snow slide that cannot bury a person, though there is a danger of falling. Unlikely, but possible risk of injury or death to people. length <50 m
volume <100 m³
2 - SmallStops within the slope. Could bury, injure or kill a person. length <100 m
volume <1,000 m³
3 - MediumRuns to the bottom of the slope. Could bury and destroy a car, damage a truck, destroy small buildings or break trees. length <1,000 m
volume <10,000 m³
4 - LargeRuns over flat areas (significantly less than 30°) of at least 50 m in length, may reach the valley bottom. Could bury and destroy large trucks and trains, large buildings and forested areas. length >1,000 m
volume >10,000 m³

## North American Avalanche Danger Scale

In the United States and Canada, the following avalanche danger scale is used. The United States of America —commonly referred to as the Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page

Probability and triggerDegree and distribution of dangerRecommended action in back country
Low (green)Natural avalanches very unlikely. Human triggered avalanches unlikely. Generally stable snow. Isolated areas of instability. Travel is generally safe. Normal caution advised.
Moderate (yellow)Natural avalanches unlikely. Human triggered avalanches possible. Unstable slabs possible on steep terrain. Use caution in steeper terrain
Considerable (orange)Natural avalanches possible. Human triggered avalanches probable. Unstable slabs probable on steep terrain. Be increasingly cautious in steeper terrain.
High (red)Natural and human triggered avalanches likely. Unstable slabs likely on a variety of aspects and slope angles. Travel in avalanche terrain is not recommended. Safest travel on windward ridges of lower angle slopes without steeper terrain above.
Extreme (red/black border)Widespread natural or human triggered avalanches certain. Extremely unstable slabs certain on most aspects and slope angles. Large destructive avalanches possible. Travel in avalanche terrain should be avoided and travel confined to low angle terrain well away from avalanche path run-outs.

## Canadian classification for avalanche size

The Canadian classification for avalanche size is based upon the consequences of the avalanche. Half sizes are commonly used.

SizeDestructive Potential
1Relatively harmless to people.
2Could bury, injure or kill a person.
3Could bury and destroy a car, damage a truck, destroy a small building or break a few trees.
4Could destroy a railway car, large truck, several buildings or a forest area up to 4 hectares.
5Largest snow avalanche known. Could destroy a village or a forest of 40 hectares.

[17]

## United States classification for avalanche size

SizeDestructive Potential
1Sluff or snow that slides less than 50cm (150') of slope distance.
2Small, relative to path.
3Medium, relative to path.
4Large, relative to path.
5Major or maximum, relative to path.

[17]