Avalanche control

Avalanche control or avalanche defense activities aim at the elimination and reduction of hazard and damage resulting from avalanches. [http://geosurvey.state.co.us/Default.aspx?tabid=400 "Mitigation and Land Use - Avalanches"] , Colorado Geological Survey]

There are two major groups of techniques for avalanche defense: active techniques and passive techniques, sometimes more narrowly defined as "explosive" and "structural", according to the prevalent techniques used.

Active techniques

Active techniques involve the artificial triggering of smaller avalanches which are expected to be less harmful. Small avalanches may be triggered manually by disturbing snow up the possible avalanche path. However the most common method is the use of explosives. Explosives may be delivered manually, by bombing, or by shelling. Each method has its drawbacks and advantages.

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 even a small probability of a larger avalanche is unacceptable.

Passive techniques

Passive techniques amount to slowing down, stopping, and diverting the moving snow and preventing it from moving, either completely or from moving in big masses. Passive techniques involve building various structures and some other approaches.

Avalanche control structures may be classified as follows:
*Snow retention structures (snow racks, avalanche snow bridges, snow nets), used in the upper path of probable avalanche paths
*Avalanche barriers: The main part of the avalanche barriers is based on a high tensile strength steel wire mesh, extending across the slope and reaching to the surface of the snow. The supporting effect created by the retaining surface prevents possible creeping within the snow cover and sliding of the snow cover on the terrain surface. Breaking-away of avalanches is thus prevented at the starting zone, while occurring snow movements are restricted to the extent that they remain harmless. The forces resulting from the snow pressure are absorbed by the snow nets and carried off over the swivel posts and anchor ropes into the anchor points.
*Snow redistribution structures (wind baffles, snow fences)
*Snow deflection structures used to deflect and confine the moving snow within the avalanche track. They should not deflect the avalanche sharply, because in the latter case they may be easily overrun by snow.
*Snow retardation structures (e.g. snow breakers), mostly used in small-slope parts of the avalanche track, to enhance the natural retardation
*Snow catchment structures
*Direct protection of important objects and structures, e.g., by snow sheds (avalanche sheds).

Avalanche dams, ditches, earth mounds, terraces, etc. may serve for deflection, retardation, and catchment.

Other passive methods include:
*reforestation, up the natural tree line — forests serve all the functions of artificial avalanche defenses: retention, redistribution, retardation and catchment
*snow compaction — done in ski resort areas by mechanical equipment, such as snow groomers.

ee also

* Landslide mitigation, control of a similar disaster type

References

*Jaedicke, Christian; Naaim-Bouvet, Florence; Granig, Matthias (2004) "Wind-tunnel study of snow-drift around avalanche defense structures", "Annals of Glaciology, vol. 38, p.325-330

External links

* [http://www.avalanche.org National Avalanche Center] of the United States Forest Service


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