...THE WHITE DRAGON'S WAKE...

TYPES OF          AVALANCHE 

THE MECHANISM OF AVALANCHE RELEASE 

FORECASTING SNOW AVALANCHES 

AVALANCHE CONTROL TECHNIQUES 

AVALANCHE HAZARD RATINGS 

AVALANCHE TRAINING FOR DOGS 

INFO ON THE PAGE OWNERS 

Hazards caused by avalanches be mitigated or even eliminated by the application of operational and engineering techniques. There are two fundamental methods of avalanche control: modification of terrain, and modification of the snow cover.   

Terrain modification may deflect the sliding snow away from fixed facilities to be protected, or actually prevent the avalanche release. Examples of deflecting structures are snowsheds used to protect railways and highways. They must be strong enough to support the dynamic load of sliding snow; therefore most modern snowsheds are built of reinforced concrete. Instances where sheds are impractical, the sliding snow can be diverted laterally by wedges, pylons, or diversion walls.   

The snow may also be arrested by snow dams or catchment basins in favorable terrain. Avalanches are also arrested in the outrun, or transition zone, of their paths by braking mounds conical earthen or masonary mounds four meters or more high which axe arranged in a pattern to break up the flowing snow into crosscurrents which internally dissipate its kinetic energy. All of the passive deflection structures act principally on snow sliding on the ground which may exert impact forces up to 50 tons/m2. They have less effect on the dust cloud accompanying a powder snow avalanche.  

Active avalanche defense by terrain modification is achieved with supporting structures in the avalanche release zone. These are large walls, fences, or nets arranged to retain snow and prevent avalanches from falling. Their size and spacing are designed to (1) terrace the mountainside into discrete zones, each of which has snow deposited to a surface slope less than the mean, (2) break up the the continuity of the snow surface and prevent slab formation, and (3) support snow on the mountainside in small, manageable sections. These supporting structures, mostly massive fences in modern design, must be strong enough to support creep pressures reaching tons per square meter, while at the same time being light enough for economical transport and erection high on a mountainside. Another type of defense used in the release zone is the wind baffle, a wall or panel arranged to induce irregular wind drifting which breaks the continuity of snow slabs. They are not designed to withstand large creep pressures and are less effective than supporting structures.  

Avalanche control by snow modification does not give the high degree of protection afforded by terrain modification but is much cheaper. It commonly is used to reduce the hazard to mobile entities, such as skiers or highway traffic, which may be removed during periods of danger. The commonest technique is artificial release, which brings down avalanches at a chosen safe time and inhibits formation of large avalanches by relieving slopes of their snow burden piecemeal in small ones. Slides on small paths are sometimes intentionally released by skiing, but the preferred method is the detonation of a brisant high explosive on the snow surface close to the expected fracture line. One kilogram of TNT or its equivalent is considered the minimum reliable charge. The charge may be placed by hand, but this can be difficult and is sometimes dangerous. Artillery shells, armed with superquick point detonating fuzes, are much more efficient, for a number of targets can quickly and safely be engaged from a single gun emplacement. Principal disadvantages of artillery are limitations to military or government use and possible damage from shrapnel dispersion. Mortars, light howitzers, and recoilless rifles have all been successfully used for avalanche control; the 75mm recoilless rifle is the most practical weapon for this purpose. Where frequent artificial release is undertaken to protect a ski area or highway,, a fixed artillery emplacement permits increased efficiency by blind firing during storms or at night. Artificial release cannot be effectively employed at random. It must be based on accurate appraisal of snow and weather conditions, and careful selection of targets.  

Another snow modification technique is the application of mechanical disturbance to break up slab formation (especially soft slabs) and induce stabilization through age hardening. Skier traffic is the commonest available disturbance, while deliberate packing of the snow by foot or ski is sometimes used. Depth hoar can be satisfactorily stabilized only by intensive foot packing. Mechanical aids, such as oversnow vehicles, can seldom be used at the slope angles existing in avalanche release zones.  

THE AVALANCHE BARRIER