Prevention and mitigation begins with observing the snow pack to forecast the risk of avalanche occurrence. The forecast risk then determines the necessary interventions to reduce the hazard posed by an avalanche.
Observation and forecasting Snow pack observation studies the layering and distribution of the snow to estimate the instabilities of the snow pack and thus the risk of an avalanche occurring in a particular terrain feature. In areas of heavy human use the snow pack is monitored throughout the winter season to assess its evolution under the prevailing meteorological conditions. In contrast to heavily used avalanche terrain where forecasting is the goal of snow observation, in remote terrain, or terrain that is infrequently visited, snow pack observation elucidates the immediate instabilities of the snow pack.
Active interventions ski resort of
Tignes () installation Active techniques reduce the risk of an avalanche occurring by promoting the stabilization and settlement of the snow pack through three forms of intervention: disrupting weak layers in the snow pack, increasing the uniformity of the snow pack, and lessening the amount of snow available in snow pack for entrainment in an avalanche; this can be accomplished either by triggering smaller less hazardous avalanches, or by directly influencing the structure of the layering of the snow pack. Active avalanche control can be broadly classified into either mechanical or explosive methods. Mechanical methods are typically used in either remote terrain, smaller terrain, or less hazardous terrain; while explosive methods are used in accessible large high hazard terrain, or terrain with industrial, commercial recreational, urbanized, and transportation usage. In the smallest terrain features the simplest method of avalanche control that disrupts weak snow layers by directly walking through them, a technique referred to as boot packing. For larger features this method can extended by mechanized redistribution of snow using large tracked vehicles called
snow groomers. These two mechanical interventions can only be safely done as the snow is deposited and before it develops any instabilities. In terrain that can only be sporadically accessed, or in a highly developed snow pack that is too deep for boot packing, ski stabilization techniques are used. The first technique of ski stabilizing is a method of entering a slope called ski cutting. In this method a skier attempts to trigger a small avalanche by breaking the tensile support of the upper snow pack through a quick traverse along the top of the slope, the skier can be belayed on a rope to further protect them from being caught in an avalanche. A snow pack can then be further settled out, or stabilized, by further down slope ski traffic through it. Finally knotted cord can be used to saw through the roots of
cornices, causing the cornice to drop onto the snow pack of the slope below. This has the combined effect of reducing the objective hazard posed by the cornice, and providing a large impact force on the snow pack. team using a 105mm
recoilless rifle for avalanche control at
Mammoth Mountain in the
Inyo National Forest. Explosive techniques involve the artificial triggering of smaller less destructive avalanches, by detonating charges either above or on the snow surface. The explosives may be deployed by manually hand tossing and lowering, by
bombing from a helicopter, or by
shelling with a
howitzer,
recoilless rifle, or
air gun. In balancing the hazard to personnel with the effectiveness of the deployment method at accessing and triggering avalanche terrain, each method has its drawbacks and advantages. Among the newest methods, strategically placed remote controlled installations that generate an air blast by detonating a
fuel-air explosive above the snow pack in an avalanche starting zone, offer fast and effective response to avalanche control decisions while minimizing the risk to avalanche control personnel; a feature especially important for avalanche control in transportation corridors. For example, the Avalanche Towers (Sprengmast) Austria, and Norway use solar powered launchers to deploy charges from a magazine containing 12 radio controlled charges. The magazines can be transported, loaded, and removed from the towers by helicopter, without the need for a flight assistant, or on site personnel. Explosive control has proved to be effective in areas with easy access to avalanche starting areas and where minor avalanches can be tolerated. It is mostly unacceptable, however, in areas with human residence and where there is even a small probability of a larger avalanche. These structures can be fully enclosed, like an artificial tunnel, or consist of lattice-like elements. They are typically of robust construction considering the environments they must survive in. Snow protection is particularly important when routes cross avalanche "chutes", which are natural ravines or other formations that direct or concentrate avalanches. Snow sheds or avalanche galleries are a common sight on railroads in mountain areas, such as
Marias Pass and
Donner Pass in the
United States, or many of the
Swiss mountain railways, where tracks are covered with miles of shedding. Although unused today, the
Central Pacific Railroad had a complete rail yard under a roof on Donner Pass. They are also found on especially hazardous stretches of roadway as well. The
Trans-Canada Highway between
Revelstoke and
Golden in
British Columbia has several snow sheds covering both directions of travel to cope with the heavy snow. East of
Snoqualmie Pass in
Washington in the
northwest U.S., westbound
Interstate 90 had a snow shed midway along the east shore of
Keechelus Lake (, milepost 57.7); it was removed in 2014 in preparation for the construction of bridges to replace it. The concrete structure covered two lanes on a curve and was constructed in 1950 for
U.S. Route 10, then one lane in each direction; it marked the first time precast construction was used for a highway structure in a mountainous area and was the last remaining snow shed on an
Interstate highway.
Snow bridge . A
snow bridge,
avalanche barrier, or
avalanche fence, looks superficially similar to
snow fences, but they act differently. Snow fences are built vertically and accumulate snow on their downwind side, while snow bridges are slanted or horizontal and hold snow on their top side. Snow bridges are fastened to the slope on the upslope side by tension anchors and on the downslope by compression anchors.
Avalanche dam Avalanche dams (
anti-avalanche dams,
avalanche protection dams) are a type of avalanche control structure used for protection of inhabited areas, roads, power lines, etc., from
avalanches. The two major types are deflection and catchment
dams. Both types of avalanche dams are usually placed in the run-out zone of the avalanche and in the flatter parts of the avalanche path. In other parts of the avalanche they are ineffective because they may be easily overrun or overfilled.
permafrost-mediated
soil creep) and in conditions of heavy
rainfall and
mudflows. Avalanche nets have some drawbacks, as they are more difficult to anchor in loose ground.
Social interventions To mitigate the hazard of avalanches, social interventions reduce the
incidence and
prevalence of human avalanche involvement by modifying the behavior of people, so that their use of avalanche terrain is adapted to prevent their involvement in avalanches. Avalanche control organizations accomplish this by targeting awareness and education programs at communities that frequent avalanche terrain. Surveys of avalanche accidents have observed that most avalanches that involve people are caused by people, and of those victims many were unaware of the risk of avalanche occurrence. To address this observation, introductory awareness and education programs provide instruction in the avoidance of hazardous avalanche involvement through the recognition of avalanche terrain, the observation of snow pack instabilities, and the identification of human activities that cause avalanches. Avalanche control organizations also publicly disseminate forecasts, bulletins, warnings, and reports of avalanche activity to assist communities of avalanche terrain users. ==Response and recovery==