An avalanche (also called a snowslide or snowslip) is a flow of snow down a slope, in the form of a fluid disruption of a cohesive snowpack, where the flow is driven by gravity, and affected by turbulence, friction, drag, and resistance. Avalanches are triggered by mechanical failures in the snowpack, and after initiation will accelerate, growing in mass, and volume as it entrains more snow. Very fast avalanches will mix snow with air forming a powder snow avalanche. Although primarily composed of flowing snow, air, and water, large avalanches have the capability to entrain ice, rocks, trees, and other material on the slope. Avalanches are distinct from mudslides, rock slides, and serac collapses on icefalls; and are distinguishable from the slower cohesive movements of the snowpack due to creep, and glide deformations (cite McClung, what page?). In mountainous terrain, avalanches are among the most serious objective natural hazards to life and property, with their destructive capability resulting from their potential to carry enormous masses of snow at high speeds (cite freedom of the hills? peer review actuarial literature?).
Avalanche regions
editAvalanches occur in geographical constrained domains, typically in mountainous terrain; although under rare conditions they have occurred on steep unsupported slopes outside of mountain ranges.
Mountainous regions
editAvalanches are endemic to many of the mountain ranges that accumulate standing snowpacks, and occur only in specific terrain features. Most avalanches commonly occur during cold, winter, or spring seasons when snow storms are more frequent. In mountain ranges at either high elevations or high latitudes, avalanches can occur during any part of the year; in particular glacier movements may cause ice, and snow avalanches at any time. Many mountain ranges that are either populated, or near populations have seasonal avalanche forecast, control, mitigation, and rescue programs.
| Range | Start of Season | End of Season | Upper Start Zone Elevation | Lower Start Zone Elevation | Upper Track Elevation | Lower Runout Elevation | Forecasts and Bulletins |
|---|---|---|---|---|---|---|---|
| Alps | Month | Month | Metres | Metres | Metres | Metres | Name(s) or none |
| Andes | Month | Month | Metres | Metres | Metres | Metres | Name(s) or none |
| Atlas | Month | Month | Metres | Metres | Metres | Metres | Name(s) or none |
| Himalayas | Month | Month | Metres | Metres | Metres | Metres | Name(s) or none |
| Rockies | Month | Month | Metres | Metres | Metres | Metres | Name(s) or none |
| Southern Alps | Month | Month | Metres | Metres | Metres | Metres | Name(s) or none |
| Urals | Month | Month | Metres | Metres | Metres | Metres | Name(s) or none |
Other regions
editIn rare circumstances avalanches have occurred outside of mountain ranges, under extreme meteorological conditions. Avalanches outside of mountainous terrain result from the rapid storm loading of a large amount of snow on steep slopes that lacks support for the new snow. Atypical slopes may even be engineered, such as in the case of roof avalanches(cite Daffern). For example, there have been sporadic avalanches on steep slopes during extreme winter storms in Eastern Canada (cite 2013 East coast avalanche); notably a hillside avalanche in Quebec resulted in NN fatalities (cite Quebec avalanche).
Avalanche types
editAvalanches are cross-classified by the mode of failure propagation, and the type of flow transport. There is only one mechanism by which an avalanche comes to rest, through the dissipation of inertial energy into friction. There are two modes of failure propagation, loose snow, and slab avalanche(cite McClung, what page?). There are three types of flow transport, dry snow, wet snow, and powder snow(cite Daffern, what page?). All avalanches, in flowing downhill, release the stored gravitational potential of the snowpack into the inertial energy of the avalanche flow mass. An avalanche comes to rest when the inertial energy of the flow mass has been dissipated through friction, both internally within the flow, and externally between the flow and the environment. As a result, as an avalanche comes to rest both the debris, and the environment are heated, to some small degree. Once at rest the avalanche debris rapidly thermally equilibrates to the surrounding environment, and refreezes(cite McClung, what page?). In North America this observed process is colloquially referred to as the debris setting up(cite Daffern, what page?).
Loose
editPoint releases, sloughing, tear drop, ploughing, and tight fans, lack of propagation of failure...
Slab
editFracturing and propagation of failure
Dry
editDry flow mostly confined to track. (Should we include spin drift in here? Spin drift flows result from the wind transport of snow into steep drainages). Large spin drift flows are capable of knocking ice climbers off of well established footings.
Wet
editWet flow confined to track
Powder
editAirborne flow, which is a type of gravity current(cite McCaffery, Kneller, & Peakall, what page?)
Avalanche triggers
editAvalanches are triggered when the load on a snowpack exceeds the strength of a snowpack. While the triggers of an avalanche may be spontaneous or random, under conditions favourable to their formation, avalanches are neither rare nor random. The triggers of an avalanche are broadly classified as being either natural, or human(cite McClung, what page?).
Natural
editNaturally triggered avalanches result from either the addition of load until failure, or the weakening of layers within the snowpack until failure. Precipitation, as either snow or rain; wind loading, the deposition of snow transported from another location by wind; other avalanches, referred to as step down avalanches; ice falls; cornice falls; and rock falls, have all been observed as natural loading triggers. Solar and air heating; water saturation; and faceting, have all been observed as natural weakening triggers. Even in the absence of additional loads, or weakening processes, the force of gravity on a snowpack will change a snowpack over time. This change will redistribute the the loads on a snowpack, and may trigger an existing weak layer, or may further weaken a layer until it fails under the load(cite McClung, what page?, is there a better material science reference?).
Human
editHumans trigger avalanches only through the addition of load. The additional loads can be either intentional applied, in the case of avalanche control work, or unintentionally applied, in the case of many avalanche accidents(cite Daffern, what page?). Table of statistics of human activities causing unintentionally avalanches(cite Jamieson accidents, what page?)
| Activity | % of Accidents | Number of Accidents |
|---|---|---|
| Ski | 00 | 00 |
| Snowmobile | 00 | 00 |
| Climbing | 00 | 00 |
| Other | 00 | 00 |
Influencing factors
editThe primary influences on avalanches are organized into a three part conceptual model of concurrently necessary factors: terrain, weather, and snowpack (cite Fesler & Fredston). Terrain classifies the geography necessary for an avalanche. Weather classifies both the meteorological conditions necessary to accumulate a snowpack, and the conditions under which a snowpack will develop a weakness. Snowpack classifies both the layers of a snowpack, and the weakening of those layers.
Terrain
editTerrain determines the dominate weather patterns that influence a snowpack, the location and evolution of weakness in the snowpack, and the dynamics of an avalanche once the avalanche has been triggered. Continental versus coastal, elevation and slope, sun exposed versus shaded, lee versus windward, convexity versus concavity, vegitation and boulders as strength or weakness. Elements of avalanche terrain: start zone, track, runnout, trim lines
Weather
editSnow versus rain versus no precipitation, sun versus cloud, day versus night, cold air versus warm air, wind versus calm. Rapid versus slow changes, extremes versus mild.
Snowpack
editElements of, and evolution towards either stability or instability: faceting versus rounding, etc...
Natural significance
editGeological
editTransportation of minerals, weathering and exposing rock, sedimentation and mixing of sediments, etc...
Geographical
editFeed back cycle, avalanches are both shaped by the landscape, and in turn shape the landscape. Formation of trimlines, etc...
Hydrological
editPrimarily redistributes melt water availability in both time and space by transporting snow from high elevations and compacting and compressing it in low elevations. Need references to determine if it increases melt water pulses or smooths out melt water pulses. Also how do avalanches contribute to glaciation? Are they part of the growth and advancements process?
Ecological
editTrimlines, soil mixing and deposition, plant redistribution and diversification, post season use of debris piles as passage/corridor for large vertebrates, slow melt water release from debris cools streams improving aquatic habitat
Management
editAvalanche accidents are broadly differentiated into 2 categories: accidents in residential, industrial, and transportation settings; versus accidents in recreational settings. Avalanches accidents in the residential, industrial, and transportation settings are generally due to naturally triggered avalanches. In contrast, 83% of avalanches accidents in recreational settings involved avalanches that were triggered by those involved in the accident(cite Jamieson accidents 1996).
Professional
editThe purpose of professional avalanche accident emergency preparedness and disaster management is to safeguard the vulnerable members of the public who are required to use avalanche terrain, for residential, industrial, or transportation purposes. Professional avalanche management also provide, as a public service, advice to recreational users of avalanche terrain.
Forecast
editLong term observation, spanning many seasons, large exchange of information, collaboration with academic community. Spanning whole regions, or down to single slide paths. Aggregate digest and disseminate drawing comparisons and inferring trends. Aggregate from professional observations, reports of incidents professional and recreational. Disseminate back to professionals in technical form. Disseminate back to recreational in public forecasts, bulletins, advisories, and warnings.
Europe danger scale
New Zealand risk scale
North America risk scale
Prevention
editProfessional avalanche control prevents avalanches by directly stabilizing the snowpack; through either passive, or active methods. Passive snowpack stabilization involves the placement of industrially manufactured retention structures such as snow nets, snow fences, and light walls; as well trees have been used for passive stabilization in some circumstances(really, is this cite-able?). Passive stabilization both anchors the snowpack to the slope, and directs the placement of snow, through the shaping of turbulent eddies in the wind around structures. Active avalanche control reduces the likelihood, and size of avalanches by disrupting the structure of the snowpack, and by removing over burden that can result in larger avalanches. The simplest active control methods involves settling the snowpack through repeated travel, either manually, or by machine grooming. Avalanche professionals also activiely control avalanches by triggering smaller avalanches in start zones, either manually, or with concussive devices. Manual triggering of avalanches can involve either travelling over the snowpack to generate additional load, such as ski cutting a slope, or by releasing cornices onto slopes, through cutting, or explosives. Concussive devices make extensive use of explosives to trigger avalanches. Explosive charges are delivered by a number of methods including hand tossed charges, helicopter dropped bombs, Gazex concussion lines (cite TAS), and ballistic projectiles launched by air cannons and artillery.
Mitigation
editThe first tool available to avalanche professionals to mitigate the impact of avalanches in residential, industrial, and transportation settings is to close or limit public access to the areas affected by avalanches. Closures may take the form of permanent by-laws that prohibit the construction of structures in avalanche terrain, or operations within avalanche terrain (cite example of European zoning law); or closures may be temporary, limiting access to avalanche terrain during times of dangerous conditions (cite example of Parks Canada closure policy). When closures are not feasible, because access to, or through, avalanche terrain must be maintained at all times, permanent in-situ structures can be erected to protect vulnerable infrastructure from the impact of avalanches.
Artificial barriers, by either slowing avalanches, diverting avalanches, or stopping avalanches, are an effective means to mitigate the affects of avalanches. They are usually placed right above the structures that they are intended to protect, such as roads, rails, buildings, resorts, mines, and forestry operations; although they can also be used to channel avalanches into other runout terminus, and barriers. Snow nets, and snow fences can be used to slow avalanches, as well as being retention structures; occasionally landscaped earth mounds are used to slow avalanches. Trees can either be planted or they can be conserved, to reduce the strength of avalanches. Larger landscaped barriers called avalanche dams,constructed from concrete, rocks, and earth, are used as diversions, and catchments for avalanches. Along transportation corridors, large shelters, called snow sheds, are used to protect traffic from avalanches. Historically, in the Alps, some buildings in avalanche paths had the impact of avalanches mitigated through architectural designs featuring reinforced streamlined wedges facing up slope, or reinforced roofs streamlined into the up slope (there must be some good mechanical engineering literature).
Response
editThe goal with all responses to avalanche accidents is timeliness (quote stats on survival rates). In industrial, residential, and transportation settings avalanche accident response is focused on the search for, rescue, and recover of general members of the public; who are not anticipated to be carrying personal protective equipment associated with travel in avalanche terrain. Professional avalanche technicians will carry out planned, prepared, and organized searches that can use trained scenting dogs, probe lines, consisting of dozens of searchers, and Recco radar systems to search for clothing, and equipment with embedded reflector tags (cite Recco website). Upon location of an avalanche accident victim, rescue and recover is carried out through either manual digging by an organized team (cite paper on new conveyor belt), or in very large and solid avalanche debris with mechanized earth (re)movers.
Recreational
editThe purpose of recreational avalanche accident emergency preparedness and disaster management is to safeguard small groups of people who intentionally enter avalanche terrain in the pursuit of sporting and recreational objectives. Frequently, recreational use of avalanche terrain occurs in remote, wilderness, and back-country environments that have limited, or distant access to roads and rails, and are outside of areas with regular seasonal professional avalanche control programs.
Forecast
editConsume professional forecasts, done on the fly while travelling, takes into account local variability
Prevention
editAvoidance and safe travel (know to be effective)(cite McCammon & Haegeli). limited control work: cornice release, ski cutting (any peer reviewed research indicating these make difference?)
Mitigation
editPersonal protective equipment (cite BD, BC , Baryvox, Ortovox), exit strategies, swimming, group size, numbers on slope, numbers for rescue, inhibitors to decision making and effective response. Low consequence versus high consequence terrain
Response
editThe timeliness of response is as critical in the recreational setting as it is in professional setting, as such the first response to an avalanche accident is to search for, and rescue survivors; followed by seeking help. Beacons and other personal protective devices, hasty searches, companion rescue, organized searches, organized digging. Timeliness, search first get help latter
Observation
editTie observation methods into preceding management framework, focus on the intent of each method, this is not a how to manual
Monitoring
editResidential, transportation, and industrial monitoring. Ski hill, cat ski, heli-ski and other snow operation monitoring. Monitoring for forecasts and bulletins for recreational users
European Size Scale
New Zealand Size Scale
North American Size Scale
Controlled snow plots
editWeather stations, and precipitation meters. Tilt boards, new snow boards, etc...
Field tests
editStudy pits, saw propagation (yeah!!!), compression test, shovel shear, hand pits, rutschblock, extended column etc...(most of these have validation studies backing them)
Cultural significance
editAs a form of disaster, avalanche accidents are a source of sensationalist news coverage in the mainstream and popular media; provided the avalanche either has a large human impact, or the people involved have a large degree of notoriety (cite Rodriguez, Diaz, and Aguirre). In fiction and poetry avalanches have been used as dramatic and romantic motivation to the narrative (could cite Icefields as example, I guess). Recently ski, snowboard, and snowmobile films have highlighted surviving avalanche accidents as a feats of athletic prowess and bravery (McCammon, maybe?).
Notable avalanches
editClean up the list from the current page. A table would be nice, of dates, injuries, fatalities, locations, size estimates, and brief description
| Date | Location | Size | Fatalities | Injuries | Description |
|---|---|---|---|---|---|
| Millions of years ago | Pangea | Class one billion | All the dinosaurs | Most mammals | Thats right, the biggest avalanche every wiped out the dinosaurs |
| Yesterday | My backyard | smaller than your brain | My pride | and dignity | Shovelling out the dog run |
Use in fiction and myth
editI worship Ullr
Common misconceptions
editloud noises, etc... Spitting in burial
Ongoing research
editThe scientific and academic study of avalanches spans many disciplines, because of the diverse causes, mechanics, and consequences of avalanches. The state of the art in avalanche research is annually discussed at the International Snow Science Workshop.
Geophysics
editPhysics and geophysics. Fluid dynamics, velocities, impact pressures, snowpack mechanics and thermodynamics, cystallography. NASA microwave remote sensing, Norway topography and texture remote sensing
Engineering
editEngineering, commercial, industrial, research, and development. Control system R&D, structure and architecture R&D. Personal protective equipment R&D
Psychology
editSociology, psychology, and group dynamics. Design and validation of design making frameworks, courses, public information systems