Avalanche control

Last updated

An avalanche snow bridge near a ski-resort in Vorarlberg SilvrettaNova 11.jpg
An avalanche snow bridge near a ski-resort in Vorarlberg

Avalanche control or avalanche defense activities reduce the hazard avalanches pose to human life, activity, and property. [1] Avalanche control begins with a risk assessment conducted by surveying for potential avalanche terrain by identifying geographic features such as vegetation patterns, drainages, and seasonal snow distribution that are indicative of avalanches. From the identified avalanche risks, the hazard is assessed by identifying threatened human geographic features such as roads, ski-hills, and buildings. Avalanche control programs address the avalanche hazard by formulating prevention and mitigation plans, which are then executed during the winter season. The prevention and mitigation plans combine extensive snow pack observation with three major groups of interventions: active, passive and social - sometimes more narrowly defined as "explosive", "structural", and "awareness" according to the most prevalent technique used in each. [1] Avalanche control techniques either directly intervene in the evolution of the snow pack, or lessen the effect of an avalanche once it has occurred. For the event of human involvement, avalanche control organizations develop and train exhaustive response and recovery plans.

Contents

Prevention and mitigation

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

Avalanche blasting in the French ski resort of Tignes (3,600 m or 11,800 ft) Avalanche Blasting.jpg
Avalanche blasting in the French ski resort of Tignes (3,600 m or 11,800 ft)
Gazex installation Gazex 15 (cropped).JPG
Gazex 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.

U.S. Forest Service team using a 105mm recoilless rifle for avalanche control at Mammoth Mountain in the Inyo National Forest. 106mm Recoilless Rifle.jpg
U.S. Forest Service 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. [1]

Permanent interventions

Forest and structures to protect against avalanches. Schutzwald-Lawinenverbauung.jpg
Forest and structures to protect against avalanches.

Permanent techniques slow, stop, divert, or prevent snow from moving; either completely or to enough of an extent that the destructive forces are significantly lessened. Permanent techniques involve constructing structures and modifying terrain for purposes classified as: [1]

A single intervention may fulfill the needs of multiple classes of purpose, for example, avalanche dams, ditches, earth mounds, and terraces are used for deflection, retardation, and catchment. Other passive methods include:

Snow shed

Trains passing in an avalanche gallery on the Wengernalpbahn in Switzerland. WAB Allmend Lawinengalerie Sommer.jpg
Trains passing in an avalanche gallery on the Wengernalpbahn in Switzerland.

A snow shed or avalanche gallery is a type of rigid snow-supporting structure for avalanche control or to maintain passage in areas where snow removal becomes almost impossible. They can be made of steel, prestressed concrete frames, or timber. [2] [3] 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 ( 47°21′18″N121°21′57″W / 47.355°N 121.3658°W / 47.355; -121.3658 , milepost 57.7); it was removed in 2014 in preparation for the construction of bridges to replace it. [4] [5] The 500-foot (150 m) 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. [6]

Snow bridge

Snow bridges in Switzerland. Verbauung Tanngrindel.JPG
Snow bridges in Switzerland.

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.[ citation needed ]

Snow bridges are fastened to the slope on the upslope side by tension anchors and on the downslope by compression anchors. [7]

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. [8]

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. [8]

Avalanche net

Avalanche nets (snow avalanche protection nets, snow nets) are flexible snow supporting structures for avalanche control, constructed of steel or nylon cables or straps held by steel poles, optionally supplied with compression anchors downhill. They are installed in the upper parts of potential avalanche paths to prevent snow from starting to slide into an avalanche, or to retard the slide. [1]

Snow avalanche nets have the following advantages compared to rigid supporting structures (snow fences, snow racks, snow sheds):

Avalanche nets have some drawbacks, as they are more difficult to anchor in loose ground.[ compared to? ]

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

Avalanche control organizations plan for, and respond to, avalanches. Typical responses span from clearing transportation corridors of avalanche debris, to repairing industrial and recreational facilities, to search, rescue, and recovery. To improve the outcome of human avalanche involvement avalanche control organizations offer training and education to both professionals and recreational amateurs in avalanche preparedness.

Professional preparedness

Professional responses to avalanches are targeted at avalanches involving the general unprepared public. When avalanches are forecast to occur, avalanche terrain to which the general unprepared public is exposed will be closed, and after the avalanches have occurred the area is cleared of debris, and repaired. When unexpected avalanches occur that involve the general unprepared public, avalanche control organizations respond with large professionally organized search teams involving probe lines, and trained search and rescue dogs.

Amateur preparedness

Recreational response to avalanches involves the rapid formation of an ad hoc search and rescue team. The ad hoc search and rescue teams rely on all the participants having prepared for a potential avalanche by carrying the correct search and rescue equipment, and undergoing the appropriate training.

See also

Related Research Articles

<span class="mw-page-title-main">Mountaineering</span> Sport of mountain climbing

Mountaineering, mountain climbing, or alpinism, is a set of outdoor activities that involves ascending mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas that have become sports in their own right. Indoor climbing, sport climbing, and bouldering are also considered variants of mountaineering by some, but are part of a wide group of mountain sports.

<span class="mw-page-title-main">Snow</span> Precipitation in the form of ice crystal flakes

Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughout its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.

<span class="mw-page-title-main">Landslide</span> Natural disaster involving ground movement

Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, shallow or deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environments, characterized by either steep or gentle slope gradients, from mountain ranges to coastal cliffs or even underwater, in which case they are called submarine landslides.

<span class="mw-page-title-main">Flood</span> Water overflow submerging usually-dry land

A flood is an overflow of water that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrology and are of significant concern in agriculture, civil engineering and public health. Human changes to the environment often increase the intensity and frequency of flooding, for example land use changes such as deforestation and removal of wetlands, changes in waterway course or flood controls such as with levees, and larger environmental issues such as climate change and sea level rise. In particular climate change's increased rainfall and extreme weather events increases the severity of other causes for flooding, resulting in more intense floods and increased flood risk.

<span class="mw-page-title-main">Geography of Andorra</span> Geographical features if Andorra

Andorra is a small, landlocked country in southwestern Europe, located in the eastern Pyrenees mountain range and bordered by Spain and France. With an area of 468 km², it is the sixth smallest country in Europe and also the largest of the European microstates.

<span class="mw-page-title-main">Avalanche</span> Rapid flow of a mass of snow down a slope

An avalanche is a rapid flow of snow down a slope, such as a hill or mountain.

<span class="mw-page-title-main">Ski mountaineering</span> Skiing discipline

Ski mountaineering is a skiing discipline that involves climbing mountains either on skis or carrying them, depending on the steepness of the ascent, and then descending on skis. There are two major categories of equipment used, free-heel Telemark skis and skis based on Alpine skis, where the heel is free for ascents, but is fixed during descent. The discipline may be practiced recreationally or as a competitive sport.

<span class="mw-page-title-main">Geological hazard</span> Geological state that may lead to widespread damage or risk

A geologic hazard or geohazard is an adverse geologic condition capable of causing widespread damage or loss of property and life. These hazards are geological and environmental conditions and involve long-term or short-term geological processes. Geohazards can be relatively small features, but they can also attain huge dimensions and affect local and regional socio-economics to a large extent.

<span class="mw-page-title-main">Rockfall</span> Rocks fallen freely from a cliff, roof, or quarry

A rockfall or rock-fall is a quantity/sheets of rock that has fallen freely from a cliff face. The term is also used for collapse of rock from roof or walls of mine or quarry workings. "A rockfall is a fragment of rock detached by sliding, toppling, or falling, that falls along a vertical or sub-vertical cliff, proceeds down slope by bouncing and flying along ballistic trajectories or by rolling on talus or debris slopes."

<span class="mw-page-title-main">Heliskiing</span>

Heli-skiing is off-trail, downhill skiing or snowboarding where the skier reaches the top of the mountain by helicopter, instead of a ski lift.

<span class="mw-page-title-main">1999 Galtür avalanche</span> Avalanche in Galtür, Austria

The Galtür avalanche occurred on 23 February 1999 in the Alpine village of Galtür, Austria. At 50 m (160 ft) high and traveling at 290 km/h (180 mph), the powder avalanche overturned cars, destroyed buildings and buried 57 people. By the time rescue crews managed to arrive, 31 people had died. It was considered the worst Alpine avalanche in 40 years. Three major weather systems originating from the Atlantic accounted for large snowfalls totaling around four meters in the area. Freeze-thaw conditions created a weak layer on top of an existing snow pack; further snow was then deposited on top. This, coupled with high wind speeds, created large snow drifts and caused roughly 170,000 tons of snow to be deposited.

Hydrometeorology is a branch of meteorology and hydrology that studies the transfer of water and energy between the land surface and the lower atmosphere. Hydrologists often use data provided by meteorologists. As an example, a meteorologist might forecast 2–3 inches (51–76 mm) of rain in a specific area, and a hydrologist might then forecast what the specific impact of that rain would be on the local terrain.

In environmental engineering, the flood mitigation involves the management and control of flood water movement, such as redirecting flood run-off through the use of floodwalls and flood gates, rather than trying to prevent floods altogether. It also involves the management of people, through measures such as evacuation and dry/wet proofing properties. The prevention and mitigation of flooding can be studied on three levels: on individual properties, small communities, and whole towns or cities. The costs of protection rise as more people and property are protected. The US FEMA, for example, estimates that for every $1.00 spent on mitigation, $4.00 is saved.

Landslide mitigation refers to several man-made activities on slopes with the goal of lessening the effect of landslides. Landslides can be triggered by many, sometimes concomitant causes. In addition to shallow erosion or reduction of shear strength caused by seasonal rainfall, landslides may be triggered by anthropic activities, such as adding excessive weight above the slope, digging at mid-slope or at the foot of the slope. Often, individual phenomena join together to generate instability over time, which often does not allow a reconstruction of the evolution of a particular landslide. Therefore, landslide hazard mitigation measures are not generally classified according to the phenomenon that might cause a landslide. Instead, they are classified by the sort of slope stabilization method used:

The system safety concept calls for a risk management strategy based on identification, analysis of hazards and application of remedial controls using a systems-based approach. This is different from traditional safety strategies which rely on control of conditions and causes of an accident based either on the epidemiological analysis or as a result of investigation of individual past accidents. The concept of system safety is useful in demonstrating adequacy of technologies when difficulties are faced with probabilistic risk analysis. The underlying principle is one of synergy: a whole is more than sum of its parts. Systems-based approach to safety requires the application of scientific, technical and managerial skills to hazard identification, hazard analysis, and elimination, control, or management of hazards throughout the life-cycle of a system, program, project or an activity or a product. "Hazop" is one of several techniques available for identification of hazards.

Avalanche Skills Training is a standardized form of avalanche training in Canada. Merriam-Webster Dictionary defines an avalanche as a large mass of snow, ice, earth, rock, or other material in swift motion down a mountainside or over a precipice. Although Avalanche Skills Training (AST) is typically learned by backcountry skiers and snowboarders, it is commonly recommended for all people who want to explore the backcountry by snowmobiling, snowshoeing, hiking, and all other backcountry activities. The training is provided in two levels: AST 1 and AST 2. AST 1 includes basic snow study and training on the use of a transceiver, probe and shovel in companion rescue. AST 1 is taught in two parts: a classroom session including lectures, PowerPoints, videos, demonstrations, and group exercises, along with a field session which includes various practices while on the mountain. To move on to AST 2, it is required to complete the AST 1 course. AST 2 concentrates on advanced snow study. AST 2 is taught through multiple days, typically including one day in a classroom setting for theory and discussions, along with multiple days of advanced training on the mountain. Further training instruct the use of explosives for avalanche control. AST is supported by the Canadian Avalanche Association and the Alpine Club of Canada. AST is offered by various companies which are usually offered in the backcountry of Canada due to the length of their season of snow and cold weather, making it an exceptional location to conduct avalanche skills training. It is important to note that avalanche skills training is not for everybody. There have been 37 deaths in the United States recorded from avalanche accidents in 2021 alone. The information learned through the avalanche skills training courses is to prepare for identifying potential hazards in the back-country, understanding the hazards communicated through an avalanche forecast, identifying and managing your risk, recognizing avalanche terrain, planning trips that avoid or minimize exposure to avalanche terrain, and rescuing your partners if they are caught in an avalanche.

<span class="mw-page-title-main">Avalanche rescue</span> Rescue of people buried in avalanches

Avalanche rescue involves locating and retrieving people who have been buried in avalanches.

<span class="mw-page-title-main">Ice dam (roof)</span>

An ice dam is an ice build-up on the eaves of sloped roofs of heated buildings that results from melting snow under a snow pack reaching the eave and freezing there. Freezing at the eave impedes the drainage of meltwater, which adds to the ice dam and causes backup of the meltwater, which may cause water leakage into the roof and consequent damage to the building and its contents if the water leaks through the roof.

<span class="mw-page-title-main">Stevens Pass Historic District</span> Historic district in Washington, United States

The Stevens Pass Historic District is an area within a large rectangle 3.2 by 18.2 miles and extends from the Martin Creek Tunnel on the western slope of the crest to the eastern portal of the present Cascade Tunnel above Nason Creek on the eastern slope. The area is ruggedly mountainous and the terrain is covered with timber and granitic outcroppings. The Cascade Range interfered with the Great Northern Railway effort to develop a deep water western terminus in Puget Sound. A gap in the Cascade Range, at Stevens Pass, was found suitable at an elevation slightly in excess of 4,000 feet (1,200 m) about 45 miles (72 km) east of Seattle. The first effort an elaborate switchback system, replaced by a tunnel which was itself replaced by a second tunnel.

References

  1. 1 2 3 4 5 "Mitigation and Land Use - Avalanches" Archived September 17, 2006, at the Wayback Machine , Colorado Geological Survey
  2. Photographs of avalanche defences, FAO corporate document repository
  3. FAO, Staff. "Avalanche and torrent control in the Spanish Pyrenees". National Forests Organization of Spain. Patrimonio Forestal del Estado. Retrieved 2016-12-01.
  4. McFadden, Meagan; Smith, Jason (March 13, 2013). "New bridges get green light to replace snowshed east of Snoqualmie Pass". State of Washington. Department of Transportation. Retrieved June 21, 2017. (dead link 8 March 2019)
  5. "I-90 Snowshed Removal Time Lapse". YouTube. Washington State Department of Transportation. April 16, 2016. Archived from the original on 2021-12-12. Retrieved June 21, 2017.
  6. Derrey, Summer (March 18, 2014). "The I-90 Snowshed Retires After 64 Years!". WSDOTBlog.BlogSpot.com. Retrieved June 21, 2017. (dead link 8 March 2019)
  7. "Steel snow bridges"
  8. 1 2 The design of avalanche protection dams. Recent practical and theoretical developments
  9. Nets are less damaged by rocks because their flexible structure dissipates the kinetic energy of falling rocks, see "Protective barrier, in particular for mountainous places", patent description
  10. "Snow-supporting structures in permafrost" [ permanent dead link ]