Actions You Should Take if Caught
If caught in an avalanche:
If caught by a powder avalanche:
As the avalanche slows:
When the avalanche has stopped:
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Actions You Should Take if Caught
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The Avalanche Terrain Exposure Scale - ATES has three different classes to describe the exposure of a backcountry trip to avalanche hazard: SIMPLE, CHALLENGING and COMPLEX. The table below describes the basic characteristics of the three different classes.
| Description | Class | Terrain Criteria |
 |
1 | Exposure to low angle or primarily forested terrain. Some forest openings may involve the runout zones of infrequent avalanches. Many options to reduce or eliminate exposure. No glacier travel. (Photo: Grant Statham) |
 |
2 | Exposure to well defined avalanche paths, starting zones or terrain traps; options exist to reduce or eliminate exposure with careful routefinding. Glacier travel is straightforward but crevasse hazard may exist. (Photo: Grant Statham) |
 |
3 | Exposure to multiple overlapping avalanche paths or large expanses of steep, open terrain; multiple avalanche starting zones or terrain traps below; minimal options to reduce exposure. Complicated glacier travel with extensive crevasse bands or icefalls. (Photo: Bill Mark) |
A period of Avalanches associated with a storm or warm weather. For snow storms, the cycle typically starts during the storm and ends a few days after a storm
Loose avalanches are usually confined to surface layers, and therefore are often small. Loose snow avalanches:
Small loose snow avalanches (size 1) are often referred to as "sluffs". Since loose snow avalanches start from a point and fan out, they are also called "point releases".
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Avalanche Motion
Avalanches move in a variety of ways depending upon their speed and composition.
Avalanche Speeds
The speed of the front of an avalanche depends on the type of motion, slope incline, roughness of ground, and the depth of the flow. Typical ranges of speed in avalanche tracks are:
Gliding motion: 0 - 40 km / hour
Wet flow: 40 - 100 km / hour
Dry flow: 40 - 200 km / hour
Powder: 70 - 250 km / hour
Gliding Motion
Gliding motion occurs in avalanches moving up to 40 km per hour. After the snow fails and has overcome the initial static friction, it accelerates rapidly. Slabs break into smaller fragments and snow glides along the surface with little mixing and turbulence.
People caught in gliding motion avalanches may be able to remain at the surface by making swimming motions, Skis and poles can act like anchors and tend to pull a person down.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Dry Flowing Motion
When speeds exceed about 40 km per hour avalanches become turbulent and flowing motion results. A fully developed, dry flowing avalanche contains a dense core of snow particles (typically 0.1 to 0.3 m in diameter). Fine particles mix with air at the front and along the upper surface of the moving snow forming a powder cloud. Speed tends to be greater in the center of the flow and the avalanche generally moves along the surface of the terrain, uninfluenced by small irregularities.
After dry flowing motion stops, debris deposits have a fairly uniform surface.
A person caught in the dense core of dry flowing avalanches may be pulled down and tossed up repeatedly. Strong swimming motions can increase the chance of remaining on the surface.
Powder avalanches consist of fine particles of snow suspended in air. They often accompany dry flowing avalanches but become pure powder avalanches when the separate from the dense core that forms the main mass of flowing avalanches. Separation may occur when the avalanche falls over a cliff, when the powder cloud overflows a channel which the core continues to follow, or in the runout zone where the powder often covers a longer distance than the denser core material.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Wet Flowing Motion
Wet snow avalanches develop in the same manner as dry snow avalanches but have no powder cloud. The moving snow is dense and composed of rounded particles with a diameter of 0.1 m to rounded lumps of several metres, or a mushy mass.
Wet snow avalanches tend to flow in channels and are easily deflected by irregularities in the terrain.
After wet flowing motion stops, deposited debris commonly has channels and ridges on the surface.
Because of their high density, wet avalanches are much more difficult to fight against than dry avalanches.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
An avalanche path is a specific location where avalanches occur. Avalanche paths are often sub-divided into three sections: the starting zone, the track and the runout zone.
The starting zone is where unstable snow fails and begins to move. Characteristics of the starting zone that are significant include the slope incline, orientation to wind, orientation to sun, roughness of ground, forest cover, differences in elevation, and trigger points.
The track is the slope below the starting zone which connects the starting zone with the runout zone. (In short avalanche paths, the track is often ill defined.)
The runout zone is the area where avalanches typically decelerate and stop. The runout zone may be divided into an area where the bulk of snow is deposited and an area affected only by powder avalanches.
An avalanche path may contain a single track fed by multiple starting zones which are separated by terrain features such as ridges or forest. Different starting zones in a path may also be distinguished by aspect and elevation. It is possible for several starting zones feeding a track to release avalanches simultaneously or within a short time of one another.
Differences in Elevation
When evaluating terrain it is important to consider the effects of elevation on the snowpack. As a general rule, high alpine slopes are exposed to more wind, colder temperatures, and greater snowfall, while lower slopes are often subject to significant changes in temperature. (Such "rules of thumb" while usually accurate, may not always hold true.)
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The volume and mass of avalanches varies widely. Mass may range from several tonnes to 500,000 tonnes. The Canadian Avalanche Size Classification if given below.
Avalanches can be highly destructive. An average avalanche produces impact forces of 30 to 100 kiloPascals (kPa). This is equal to about 3 to 10 tonnes per square metre or 600 to 2000 pounds per square inch.) Large avalanches can generate up to 300 kPa. Dry flowing avalanches are generally most destructive because they combine high speed with a dense core. Powder avalanches have a much lower density and are less destructive despite their high speed.
Canadian Avalanche Size Classification
From the deposited snow, the destructive potential of the avalanche is estimated and assigned a size number. It is imagined that the objects referred to in the size classification (people, cars, trees) were located in the track or at the beginning of the runout zone and it is decided what the avalanche could have done to them.
Note: Half sizes, from 1.5 to 4.5, may be used to describe avalanches that are between two size classes. The destructive potential of avalanches is a function of their mass, speed, and density as well as the length and cross section of the avalanche path.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Large Hazardous avalanches are usually slab avalanches. Slab Avalanches:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Once in motion, avalanches can accelerate rapidly in the starting zone and maintain their motion when average track inclines are as low as 15 to 25 degrees, which is less than the incline required for avalanches to start. This is possible because the friction of snow in motion is less than the friction of snow at rest.
Rough ground, a common condition at the beginning of winter, reduces the speed and distances that avalanches run.
All avalanches tend to move down the fall line, but dry flowing and powder avalanche are not always confined by lateral boundaries They can jump gullies, overrun obstructions, take unexpected paths, or meander from side to side in a deep channel.
Wet snow avalanches typically remain in the fall line and/or confining terrain features such as channels or gullies.
Confined avalanches have a greater depth of flow, concentrated mass, and higher speeds making them more hazardous than avalanches on open slopes.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
An electronic device worn by people in avalanche terrain. In transmit mode, it constantly transmits a radio signal which is stronger at close range. If some one with a transmitting transceiver is buried, the other members of the group can switch their transceivers into receive mode and follow a search pattern that locates the strongest signal. The person is then found by probing and shoveling.
In the ten year period from 1998 to 2007, there was an average of 12 recreational avalanche fatalities, and many more injures, each year in Canada. Many of the victims knew how to recognize dangerous conditions. Some even had formal avalanche training. So why did they get caught?
Growing evidence suggests that many avalanche victims died because they lacked a simple, systematic way of making decisions in avalanche terrain. In developing the Avaluator™, we studied more than 1400 North American avalanche accidents and interviewed dozens of avalanche experts. We wanted to learn as much as possible from past mistakes and pass this knowledge on to you.
The Avaluator™ is designed to help you make some of your most critical decisions before and during your backcountry trips. The card and its accompanying booklet focused on four key decision and travel skills:
| 1 | TRIP PLANNING (Online Avaluator™ Trip Planning Tool) |
| 2 | IDENTIFYING AVALANCHE TERRAIN |
| 3 | SLOPE EVALUATION |
| 4 |
GOOD TRAVEL HABITS
|
| Accidents are generally infrequent. These conditions are appropriate for informed backcountry travel in avalanche terrain. Use NORMAL CAUTION. You should always watch for isolated slabs and be especially careful if the avalanche bulletin mentiones deep persistent instabilities. Basic avalanche rescue skills are always essential when you travel in avalanche terrain. |
| Accidents are more frequent and are likely to occure with human or natural triggers. Travelling under these conditions requires EXTRA CAUTION. Advanced avalanche skills, including detailed trip planning, route-finding and navigation, stability evaluation, group management, rescue skills and wilderness first aid are essential for safe backcountry travel under these conditions. You can learn these skills in avalanche and other courses, but practice and humility are essential. |
| Conditions are primed for avalanche accidents. Even careful decisions can result in serious accidents. Since the margin of error is very small under red conditions, safe backcountry travel requires extremely careful planning and extensive experience. Backcountry travel under these conditions is NOT RECOMMMENDED without professional-level safety systems and guidance. |
The surface on which an avalanche runs. Not to be confused with failure plane.
At cold fronts, as the heavier, cold air advances, it pushes under and lifts the warmer lighter air. Cold fronts are often fast moving and have a steep slope causing strong lifting of the warm air, generally resulting in cloud formation and precipitation. Precipitation associated with a cold front is usually fairly intense and of relatively short duration.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
When recording field observations of weather or snowpack data a series of abbreviations or symbols are often used. In recording cloud cover a circle is drawn and a line or lines is drawn within that circle to denote the amount of cloud cover present.
Chart from "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 2007 Canadian Avalanche Association
The test as described here was developed by Parks Canada Wardens working in the Canadian Rockies in the 1970s. Similar tests were developed elsewhere. The test identifies weak layers and is most effective at finding weak layers near the snow surface. Manual taps applied to a shovel blade placed on top of a snow column cause weak layers within the column to fail. These failures can be seen on the smooth walls of the column. The test can be performed on level or sloping terrain.
A pit is dug in undisturbed snow to expose a smooth snow wall on a safe slope representative of the slopes of interest. The pit is dug to ground or until well below any possible significant weak layers (often as much as 2 metres deep). The column is not dug down to very weak layers of facets or depth hoar if these layers are likely to fail before upper weak layers of interest.
A column of snow 30cm wide (across the slope) and 30 cm upslope is created as in the diagram at left. A snow saw can assist in creating the column and making the subsequent backcut that is required. Be sure the visible walls of the column are smooth so that subtle failures can be easily seen.
A shovel is placed squarely on the surface of the column and progressively harder taps are applied to the shovel blade. Any failures are recorded. Collapse of very thin layers may be subtle and hard to detect. In most cases it is good to have a second person observe for these failures while the first person applies the taps. The size and type of crystals at the failure plane (often from the underside of the block) are also recorded. Another backcut is now made an additional 70cm below the first and the process is repeated to the bottom of the pit. The test may be repeated to verify the results or a Shovel Shear Test may be done alongside the first test location.
The amount of effort required to cause the failure is recorded as follows:
The primary objective of the compression test is the identification of weak layers. Deeper layers are generally less sensitive to taps on the shovel resulting in higher ratings. Similarly, deeper layers are less sensitive to human triggering. Experience in the Canadian Rockies suggests that layers with "very easy" or "easy" failures are more often associated with human or explosive triggering than are "moderate" or "hard" failures. Sudden failures that show up on the column wall as distinct lines seem more likely to indicate potential failure planes than rough or indistinct failures.
Caution: While the rating of effort needed to have the snow fail in compression may assist with a decision concerning snow failure, it is an inaccurate measurement of slope stability. The ratings of effort are subjective and depend on the strength and stiffness of the slab, on the size and shape of the shovel, the experience of the tester and on whether or not the test site is truly representative of the slope of interest for which the test is being applied.
NOTE: If the top surface slopes, test the near surface layers then remove a wedge of snow to level the top of the column. Once level. place the shovel blade squarely on top of the column and continue testing.
Tapping forces are not transmitted efficiently down through the column, particularly through soft layers within the column. Harder taps are generally required to cause failure in deep layers, particularly if the layers between the shovel and the weak layers contain soft snow.
Snow below the shovel that crushes and fails to support the shovel squarely should be removed. The tends to reduce the force required to cause failures in the remaining column.
Text and diagram modified after "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association. Some portions of the text modified after "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 1995 Canadian Avalanche Association
Diagrams from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The principle way in which air is heated (other than subsidence) is by coming into contact with a warm surface. Because the earth's surface heats unequally, areas of warmer air are formed amidst cooler air. Since warm air is lighter, it will tend to rise and this may lead to the formation of localized clouds and showers.
Convective Cells are generally of limited horizontal extent, so the associated precipitation is often of short duration (lasting only as long as the convective cell is Overhead), but may be very intense, as in the case of thundershowers.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
An overhanging buildup of snow, usually on the lee side of ridges. Moderate or strong winds often create a vortex on the lee side and deposit wind - blown snow at the very top of the lee slope. Cornices generally form faster during periods of high humidity.
When wind blows across a cross - loaded slope, snow is picked up from the windward side of ribs and outcrops and is deposited in lee pockets.
An advanced, generally larger, form of faceted crystal. Depth hoar crystals are striated and, in later stages, often form hollow shapes. Cup - shaped crystals are a common form of depth hoar. This type of crystal can form at any level in the snowpack but is most commonly found at the base of shallow snowpacks following periods of cold weather.
Effect of Ground Roughness
Boulders, stumps, logs, short stiff shrubs, and benches anchor the snowpack. On such ground, the snow must become deep enough to cover irregularities and form a relatively smooth surface before avalanches are possible. The threshold snow depth before avalanches can start is generally about 30cm for smooth ground (rock slabs, grass, fine scree), 60cm on average mountain terrain above timber line, and 120cm on very rough ground (boulders, large stumps). Once covered with snow, however, the stabilizing effect of large obstructions such as boulders may be reversed because they often contribute to the formation of weaker grains such as facets. Large obstructions, especially when shallowly buried, may also act as stress concentrators.
Forests
The snowpack tends to be more stable in a forest than on open slopes because trees intercept and moderate snowfall, wind and solar radiation. However, the tree cover must be dense in order to provide secure anchoring. Scattered trees with numerous openings are poor protection against avalanches
High shrubs in avalanche starting zones prevent snow from settling, often contributing to the formation of faceted grains which can result in a weaker snowpack.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Orientation to Sun
Radiation from the Sun influences snow temperature which, in turn, plays a role in determining the strength of the snow. (Snow at the melting point is usually weaker than colder snow.) Sun exposed slopes tend to have higher temperatures than shaded slopes.
In the northern hemisphere shady, cold slopes facing north and east tend to have weaker snow between December and March, because surface hoar and faceted grains (which often form weaker layers in the snowpack) are more likely to form and linger there than on sunny slopes. (Surface hoar, facets, and other snow crystals and grains are discussed more fully under "Metamorphism of Snow" and "Classification of Snow Crystals and Grains".) In the late winter and spring, however, sunny, south-facing slopes are more likely to contain weak snow due to strong warming.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The faceting process builds angular grains (facets) which bond relatively poorly to one another and other grains creating a snowpack (or layer) that is generally increasingly weak.
When the temperature gradient is strong (> 1 degree / 10cm) water vapour moves rapidly from warm grain surfaces to colder surfaces. Because the snowpack usually is warm (at or near 0 degrees C) at the ground and colder at the surface, ice sublimates from lower, warmer grains and is deposited onto colder grains higher up in the snowpack. These colder grains first develop sharp corners, then stepped facets.
If the faceting process continues, large, six - sided hollow or filled cup shaped grains called depth hoar are formed. Depth Hoar is common in Rocky Mountain climates, around large rocks and high shrubs, and where the snowpack is thin. The following conditions promote faceting:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
For a slab avalanche to start, there must be:
The most important characteristic of the snowpack with respect to formation of slab avalanches is the existence of a weak layer underlying a stronger layer or layers and / or a weak boundary between layers.
Slab avalanches start when the weight of snow layers and a trigger combine to create forces which exceed the strength of the snow. Slab avalanches are thought to occur as follows:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Fracture lines (crowns) and flanks of slab avalanches often occur at or connect characteristic terrain features where stresses are concentrated, such as convex slopes and /or where irregularities are shallowly buried or break the snow surface (e.g. rocks, trees, hummocks). Though the snow fails at these tension locations, the initial shear failure which causes and avalanche is often triggered elsewhere (often lower) on the slope. While triggers applied at stress concentration points frequently start avalanches, it is important to recognize that it is not uncommon for triggers, such as people and explosive charges, to start avalanches from locations considerable distances from where fracture lines are commonly observed.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The fracture that releases a slab avalanche spreads along a weak snowpack layer called the failure plane. The bed surface usually lies immediately below the failure plane.
The earth's surface is heated unequally because more solar radiation strikes the equator than the poles. This unequal heating creates convective cells within the atmosphere. These cells consist of hot, rising air in warm regions and cold sinking air in cool regions. The hot rising air is of a lower overall pressure and produces stormier weather. Cold sinking air is of a higher overall pressure which produces generally finer weather. (see also Barometric Pressure)
The weather we experience in the mountain regions of Western Canada is a result of the interaction between the northernmost "Polar Cell" and the "Ferrel Cell" of the mid latitudes. The contact between these two cells is known as the "Polar Front".
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
A centre of high pressure surrounded on all sides by lower pressure is referred to as a high. (A centre may be large or small.) An intensifying high is one that is increasing in pressure. Air in an intensifying high near the surface spirals downward and outwards (subsidence). An elongated region extending from a high is called a ridge.
A centre of low pressure surrounded on all sides by higher pressure is referred to as a low. A deepening low is one that is decreasing in air pressure. Air in a deepening low near the surface spirals upwards and inwards. An elongated low pressure region extending from a low is called a trough.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
(also called high - pointing or hammer - heading)
The activity in which snowmobilers drive up a steep slope, each trying to reach a higher point than the previous rider. When the sled slows at the top of the run, the rider turns down the slope.
The initial search involves a fast scan of the entire area where victims might be found (that is, from the last seen point, within the perimeters of the avalanche, and in the deposition areas). It concentrates on likely areas of burial in addition to listening for transceiver signals and looking for clues on the surface.
Initial searchers should be equipped with transceivers, probe, and shovel as well as a few wands if available.
Text and diagrams from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
There are no definitions in this section.
There are no definitions in this section.
Lifting Mechanisms
Perhaps the most important characteristic of an air mass is that air cools as it expands and as it cools, its ability to carry moisture decreases. To achieve expansion, air must be lifted from nearer the ground (where pressure is higher) to farther above the ground (where pressure is lower). Practically all precipitation is associated with lift. In terms of snow producing storms in the mountains, there are several ways in which lift significant enough to produce weather is created:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Once new snow crystals are added to the snowpack they begin to metamorphose (change). From this point on, snow crystals are technically referred to as grains (although the word crystal is still used by many practitioners). Through metamorphism, the form and size of snow crystals and grains inside a snowpack change continuously, altering the strength characteristics of the snowpack.
Metamorphism of snow in a seasonal snowpack is the result of sublimation and deposition. (Sublimation is the process of ice becoming vapour without going through a liquid state and vice versa.) During metamorphism in the snowpack, ice from grain surfaces changes into water vapour which is then deposited as ice at other grain surfaces as follows:
1.) Vapour moves from warm surfaces to cold surfaces. Because the snowpack is usually warm (at or near 0 degrees C) at the ground and cold near the surface, ice sublimates from lower, warmer grains and is deposited as ice at other grains sites as shown in the diagram to the right. Text and diagrams from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
2.) Vapour typically moves from convex surfaces (points) to concave surfaces (hollows). The sharp ends of new snow crystals becomes blunt and the space between the branches is filled. In the same manner, large grains with broad curvatures grow at the expense of small grains with sharp curvatures.
The change in snow grains as the snowpack becomes wet (snow temperature reaches 0 degrees C) and subsequently refreezes is known as melt-freeze metamorphism. This process usually occurs during late winter and spring when air temperatures are high, solar radiation is high, and cycles of melting and refreezing are common.
Melt-freeze crust layers that exist in the freeze part of the cycle can be very strong.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
There are no definitions in this section.
In a developing wave, the cold air in the trailing section of the wave moves faster than the leading section of warm air. As the heavier cold air catches up it pushes under the lighter, warm air, lifting a parcel of warmer air aloft (out of contact with the ground). This forms what is known as an occluded front, or a TROWAL (acronym for Trough Of Warm Air aLoft).
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Avalanche safety operations and rescue groups can carry out organized rescues when they are summoned to an accident site to assist in the search and recovery of victims.
Back-country travelers should not depend on organized rescue teams to come to their assistance, as usually such an effort arrives too late to make a live recovery. Many of the actions an organized rescue carries out in the field are similar to the initial search and secondary search techniques outline in Avalanche Survival, Search and Rescue. Organized rescues, however, generally involve many more resources and personnel than self-rescue efforts. Rescuers should be prepared to work in close conjunction with a dog team, carry out formal probe searches, and undertake extended rescues which may last overnight or longer.
To do all this effectively, teams must be well organized, practiced, and have preplanned responses that can be used in a variety of scenarios (a rescue plan).
The objective of a rescue plan is to provide guidelines for the organization and coordinated actions of various people and agencies in the event of an avalanche accident.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Diagram from "Avalanche Safety Course Overheads" Copyright © 1998 Canadian Avalanche Association
Rescue by Survivors
If you survive, witness, or come upon an avalanche accident there are four primary stages that must be carried out immediately:
If victims are not found using these steps, secondary search procedures are implemented.
Organizing a Self Rescue
How the following tasks are organized and assigned will depend on the size of the rescue group and the experience of its members. In small groups it may be necessary for one or two people to carry out all the tasks in a suitable order. In larger groups, tasks can be undertaken simultaneously or in conjunction with other stages of the self rescue:
Observe (or determine by clues / interviewing a witness) where the victim(s) was caught, their line of travel, and the "last seen point".
Assign a leader or rescuer who will take charge of the situation.
Determine if further avalanche hazard exists. Carefully assess whether the risks of carrying out the rescue are reasonable. It may be prudent to minimize the number of people working in areas where avalanches may strike them as they search. It may be necessary to modify some or all of the following procedures to adequately protect rescuers.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Orographic Lift takes place when a moving mass of air runs up against a physical barrier such as a mountain range and is forced upwards. This is the most powerful lifting mechanism and accounts for the majority of precipitation in Western Canada and the United States.
On the west coast, moist air coming up from the ocean can be lifted orographically and can cause precipitation without any associated storms or frontals systems. The warm and cold fronts that bring heavy snowfalls to the Coast Mountains and the Interior (Monashee / Selkirk / Purcell) Ranges often occlude or dissipate by the time they reach the Rocky Mountains. Little moisture remains and lesser amounts of snow fall on the Rockies.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Once a searcher is using the lowest receive setting on his / her transceiver, the most experienced searcher who is readily available should quickly pinpoint its location. Less experienced searchers should assist or continue the search for other victims.
Some points to keep in mind when pinpointing:
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Diagram from "Avalanche Safety Course Overheads" Copyright © 1998 Canadian Avalanche Association
Precipitation Particles are any freshly fallen "new snow" type. This can include a wide variety of specific forms that are sub - classified here. The size of the individual grains can vary wildly. When the snow crystals have significant "rime" attached the small letter "r" is added behind the graphical symbol. When snow forms under varying conditions of temperature and humidity the actual crystal type can change during a storm. Different atmospheric conditions favour crystal growth in quite different ways.
Chart from "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 1995 Canadian Avalanche Association
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
A centre of high pressure surrounded on all sides by lower pressure is referred to as a high. (A centre may be large or small.) An intensifying high is one that is increasing in pressure. Air in an intensifying high near the surface spirals downward and outwards (subsidence). An elongated region extending from a high is called a ridge.
A centre of low pressure surrounded on all sides by higher pressure is referred to as a low. A deepening low is one that is decreasing in air pressure. Air in a deepening low near the surface spirals upwards and inwards. An elongated low pressure region extending from a low is called a trough.
Text and diagrams from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Probing - The "Three Hole per Step" Technique
If a transceiver search is unsuccessful, a probe line can be set up. Recent Research (Auger and Jamieson, 1997) indicates that the three hole per step technique illustrated to the right is the most efficient means of probing and can be effective even with relatively small numbers of probers.
To set up the probe line:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Probing - The Coarse Probe
As noted above, the 3 hole per step technique has distinct advantages, particularly where a small group of rescuers must search a large area. It has been widely adopted and in some areas has almost completely supplanted the Coarse Probe Technique. The older "coarse probe" technique may still be employed where a large group of searchers, such as in an organized rescue response, arrive on scene. The classic spacing for coarse probing is as shown in the diagram at left.
Probing - The Open Space Coarse Probe
On particularly rough terrain or when fewer rescuers are available a finger - tip to finger - tip spacing is used between probers. Each prober then inserts their probe once just outside of the left foot then again just outside of the right foot. This technique provides the same probe spacing as classic coarse probing but fewer people are required for a given area (although speed diminishes).
Probing for a Vehicle
When searching for vehicles a probe spacing of 120 cm is used. Two steps forward are taken between each probe insertion to maintain this spacing.
Diagrams from "Avalanche Safety Course Overheads" Copyright © 1998 Canadian Avalanche Association
Probing - The Fine Probe
Once again, as noted above, the 3 hole per step technique has distinct advantages, particularly where a small group of rescuers must search a large area. When a protracted time has passed without success (many hours or even days) and the rescue team leader feels the hope of finding a buried avalanche victim alive has diminished to near zero, an alternative probing technique may sometimes be employed. The "fine probe" technique has a higher probability of detection (near 100%) than the coarse probe technique. Due to the fact that it uses a much closer spacing, the amount of time and manpower required to search a giver area is greater and can take as much as five times as long to probe a given area given the same manpower.
In terms of hopes of live recovery, current search theory dictates that it is likely better in most cases to use the 3 hole per step or coarse probe techniques and cover a given area twice or even three times rather than resort to fine probing during the early stages of a rescue attempt.
The spreading of a fracture or crack. The shear fractures that spread along weak layers and release slab avalanches tend to propagate further under thicker, harder slabs than under thinner, softer slabs.
There are no definitions in this section.
If you survive, witness, or come upon an avalanche accident there are four primary stages that must be carried out immediately:
If victims are not found using these steps, secondary search procedures are implemented.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
A deposit of ice from super cooled water droplets. Rime can accumulate on the windward side of rocks, trees or structures, or on falling crystals of snow. When snow crystals cannot be recognized because of rime, the grains are called graupel.
The rounding process builds rounded grains (rounds) which bond well to one another creating a snowpack (or layer) that is generally increasingly strong.
In weak temperature gradients(<1 degree / 10cm) sublimation typically moves ice from convex surfaces (points) to concave surfaces (hollows) in 2 stages:
The following conditions promote rounding:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The "rutschblock" (or glide-block) test is a slope test that was developed in Switzerland in the 1960s. This section is based on a recent Swiss analysis of rutschblock tests (Fohn, 1987) and on Canadian Research experience (Jamieson and Johnston, 1993).
Test sites should be safe, representative of the avalanche terrain under consideration and undisturbed. For example, to gain information about a wind blown slope, find a safe part of a similarly loaded slope for a test. The site should not contain buried ski or snowmobile tracks, avalanche deposits, etc. or be within about 5 m or trees where the buried layers might be disturbed by wind action or by clumps of snow which have fallen from nearby trees. Although Dr. P. Fohn (1987) recommends slope angles of at least 30 degrees, rutschblocks of 25 - 30 degrees may also give useful information (discussed below). Be aware that near the top of a slope, snowpack layering and hence rutschblock scores may differ from the slope below.
After identifying weak layers (and potential slabs) in a snow profile, extend the pit wall until its width is larger than the observers skis or snowboard (2 metres minimum) across the slope. (Do not omit the profile unless the layering is already known.) Mark the width of the block and the length of the side cuts ( 1.5 m) on the surface of the snow with a ski, ruler, etc. The block should be 2m wide throughout if the block is to be dug with a shovel. However, if the side walls are to be cur with a ski, pole, cord or saw, the lower wall should be about 2.1 m across and the top of the side cuts should be about 1.9m apart. This flaring of the block ensures it is free to slide without binding at the sides. The lower wall should be a smooth surface cut with a shovel. Dig or cut the side walls and the upper wall deeper than any weak layers that may be active. If the side walls are exposed by shoveling, then one rutschblock test may require 20 or more minutes for two people.
If the weak layers of interest are within 60cm of the surface, time can be saved by cutting both the sides and the upper wall of the block with a ski pole (basket removed) or with the tail of a ski. If the weak layers are deeper than 60cm and the overlying snow does not contain any knife-hard crusts, both the sides and the upper wall of the block can be sawed with cord which travels up one side, around ski poles or probes placed at both upper corners of the block and down the other side.
The rutschblock is loaded, and failure recorded, in the following sequence:
R1 - the block slides during digging or cutting
R2 - the skier (or snowboarder) approaches the block from above and gently steps down onto the upper part of the block (within 35cm of the upper wall).
R3 - without lifting the heels, the skier drops from straight knee to bent knee position, pushing downwards and compacting surface layers.
R4 - The skier (or snowboarder) jumps up and lands on the same compacted spot.
R5 - The skier jumps again onto the same compacted spot.
R6 - for hard or deep slabs, remove skis and jump on the same spot. / - for soft slabs or thin slabs where jumping without skis might penetrate the slab, keep the skis on, step down another 35 cm, almost to mid block and push once then jump three times.
R7 - none of the loading steps produced a smooth slope-parallel failure.
Interpretation of rutschblock tests in the starting zone:
1, 2 or 3: Block fails before the first jump. It is likely that slopes with similar snow conditions can be released by a skier, snowboarder, snowshoer or snowmobile.
4 or 5: The block fails on first or second jump. The stability of the slope is suspect. It is possible that slopes with similar snow conditions can be released by a skier, snowboarder, snowshoer or snowmobile. Other observations or tests must be used to assess the slab stability. (Snowmobiles have increased risk or staring avalanches when compared to skiers.)
6 or 7: the block does not fail on the first or second jump. There is a low (but not negligible) risk of skier, snowboarder, snowshoer or snowmobile triggering of avalanches on slopes with similar snow conditions. Other field observations and test as well as safety measures remain appropriate.
We should be very careful with interpreting slope tests since they overestimate the slope stability at least 10% of the time. (Jamieson, 2000)
The rutschblock is a good slope test but it is not a one stop stability evaluation. The test does not eliminate the need for snow profiles or careful field observations nor does it, in general, replace other slope tests such as ski cutting and explosive tests.
The rutschblock only tests those layers deeper than ski or snowboard penetration. For example, a weak layer 20 cm below the surface is not tested by skis which penetrate 20cm or more. Higher and more variable rutschblock scores are sometimes observed near the top of a slope where layering may differ from the middle and lower part of the slope (Jamieson and Johnston, 1993). Higher scores may contribute to an incorrect decision.
Rutschblock results are easiest to interpret if the tests are done in avalanche starting zones. However, since there is a general tendency for rutschblock scores to increase by 1 for each 10 degree decrease in slope angle (Jamieson and Johnston, 1993), scores for avalanche slopes can be estimated from safer, less steep slopes (as shallow as 25 degrees). Note that rutschblocks done on slopes of less than 30 degrees require a smooth lower wall and a second person standing in or near the pit to observe the small displacements (often less than 1 cm) that indicate a shear failure.
Text and diagram modified after "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association. Some portions of the text modified after "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 1995 Canadian Avalanche Association
Avalanches come to rest when the slope incline drops to below the frictional angle. Typical slope angles of runout zones are 15 degrees or less, although smaller and slower avalanches may stop on steeper terrain.
The runout distance of avalanches depends on their speed in the track, the incline and roughness of the runout zone, and the type of motion (dry, wet, powder). Powder avalanches tend to run a longer distance than flowing avalanches.
Forest and other obstructions in the track and runout zone may decrease the speed of slow avalanches but have little effect on large, fast moving avalanches.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The topic of Avalanche Search and Self - Rescue has been divided into the following sub-headings:
Action of Victims on Foot (Skis, Snowboard, Snowshoes) or Snowmobile
Action of Vicms Caught Inside a Vehicle
Rescue By Survivors
Self Rescue on Roads
Organized Rescue
Secondary Search Procedures
If a transceiver search is unsuccessful, secondary procedures must be used:
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Carrying out a self rescue when an avalanche has covered a road and vehicles are or may be involved will follow a similar procedure to that described above. There are some specific considerations, however:
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The shovel shear test provides information about the location where the snow could fail in shear. It is best applied for identification of buried weak layers and does not usually produce useful results in layers close to the snow surface. Soft snow near the surface is better tested with the tilt board and the shear frame or an improvised version of this tilt test.
A pit is dug in undisturbed snow to expose a smooth snow wall on a safe slope representative of the slopes of interest. The pit is dug to ground or until well below any possible significant weak layers (often as much as 2 metres deep). A column of snow 25cm wide (across the slope) and 35 to 40 cm upslope is created as in the diagram at left. The back of the column is not separated from the rest of the snowpack initially. A snow saw can assist in creating the column and making the subsequent backcut described below.
A cut in the back of the column is now made. This cut should be no more than 70 cm deep and should end in medium or hard snow. This is best done with a snow saw and the saw is left in place to identify the depth of the cut. A snow shovel is now inserted in this back cut as shown and force is slowly applied parallel to the top of the slope.
When the column fails in a smooth plane above the low end of the back cut, this level is marked and the depth of the shear failure and force required to cause failure are recorded. The size and type of crystals at the failure plane (often from the underside of the block) are also recorded. If the column does not shear cleanly, the block is then tilted and tapped with increasing force to see if other failures planes can be found.
Another backcut is now made an additional 70cm below the first and the process is repeated to the bottom of the pit. The test is often repeated to verify the results or a Compression Test may be done alongside the first test location.
The amount of effort required to cause the failure is recorded as follows:
NOTE: Observers are cautioned that identification of the weak layers is the primary objective of the shovel shear test. The shovel shear test is not a stability test. While the rating of effort needed to break the snow may assist with a decision concerning snow failure, it is an inaccurate measurement of snow strength. The ratings of effort are subjective and depend on the strength and stiffness of the slab, on the size, shape, length of the shovel and the length of the shovel handle.
Text and diagram modified after "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association. Some portions of the text modified after "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 1995 Canadian Avalanche Association
Sintering is usually associated with the rounding process. Water Vapour is deposited at the contact points between snow grains forming necks. These necks create strong bonds between grains, increasing snow strength.
Mechanical Hardening
Compaction from any mechanical disturbance such as boots, skis, snowmobiles, groomers, wind and avalanches breaks up large grains and brings grains into close contact, producing rapid sintering.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Size 1 avalanches are relatively harmless to people. They typically have:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Size 2 avalanches could bury, injure or kill a person. They typically have:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Size 3 avalanches could bury and destroy a car, damage a truck, destroy a small building, or break a few trees. They typically have:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Size 4 avalanches could destroy a railway car, large truck, several buildings, or a forest area up to 4 hectares (~10 acres). They typically have:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Size 5 avalanches are the largest snow avalanches known. They could destroy a village or a forest area up to 40 hectares (~100 acres). They typically have:
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
One or more cohesive layers of snow that may start to slide together.
A small avalanche usually made up of loose snow.
A primary requirement for avalanche formation is a slope incline that is steep enough for avalanches to initiate and then accelerate.
The following guidelines for using slope incline to predict avalanche size and frequency have been developed from experience.
Avalanches are rare on slopes with an incline greater than 55 degrees because the snow sluffs off frequently in small amounts.
60 to 90 degrees Avalanches are rare; snow sluffs frequently in small amounts.
30 to 60 degrees Dry, loose snow avalanches.
45 to 55 degrees Frequent small slab avalanches.
30 to 45 degrees Slab avalanches of all sizes.
25 to 30 degrees Infrequent (often large) slab avalanches; wet loose snow avalanches.
10 to 25 degrees Infrequent wet snow avalanches and slush flows.
A minimum slope angle is required to initiate a slab failure, however, a fracture may propagate to an area with less incline after initial failure on a steeper slope has occurred.
In "Avalanche Accidents in Canada - Volume 4" by Geldsetzer and Jamieson it was reported that in a sample of 184 recreational avalanche accidents, 83% of them occurred on slopes between 25 and 40 degrees and half of these fell in the range from 31 to 35 degrees. (From talk given by T. Geldsetzer, Edmonton, AB, November, 1997)
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Diagram from "Avalanche Safety Course Overheads" Copyright © 1998 Canadian Avalanche Association
Snow Crystal Grain Form
When identifying snow crystal type (or "grain form") such as when making observations in a snow profile or "snow pit" there is a standard graphical way of recording what you have observed. In Canada the "International Classification for Seasonal Snow on the Ground" (Colbeck, et al, 1990) is generally used to record the snow crystal type:
Chart from "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 1995 Canadian Avalanche Association
Text modified after "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Shovel Shear Test, Compression Test, Rutschblock Test
The information presented below is intended to provide familiarity with these test, but in no way is it intended to be a guideline for precisely how, when or where these test are employed or how they are definitively interpreted. For proper technical standards for conducting these tests please refer to "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 1995 Canadian Avalanche Association. For training in proper application of these tests in the field, consult an avalanche professional or attend a recognized training course.
We should be very careful with interpreting slope tests since they overestimate the slope stability at least 10% of the time. (Jamieson, 2000)
The tests described here are those which require very little equipment besides a shovel, knotted cord and possibly a snow saw. The tilt board and shear frame tests are not described here as they are seldom (if ever) used by recreational travelers. The tests described are:
Shovel Shear Test
Compression Test
Rutschblock Test
A slab avalanche is said to step down if the motion of the initial slab causes lower layers to slide, resulting in a second bed surface deeper in the snowpack. A step in the bed surface is usually visible.
The snow that falls during a period of continuous or almost continuous snowfall. Many operations consider a storm to be over after a day with less than 1cm of snow.
Air in an intensifying high near the surface spirals downward and outwards (subsidence and divergence). This clockwise circulation around a high pressure centre is sometime referred to as anti-cyclonic flow.
Air in a deepening low near the surface spirals upwards and inwards (lifting and convergence). This counter-clockwise circulation around a low pressure centre is sometime referred to as cyclonic flow.
Text and diagrams from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The term sun crust is often used to refer to a melt freeze crust that is more noticeable on sunny slopes than on shady slopes. However, the international definition is a thin transparent layer (also called firnspiegel) caused by partial melting and refreezing of the surface layer.
Crystals, often shaped like feathers, spikes or wedges, that grow upward from the snow surface when air just above the snow surface is cooled to the dew point. The winter equivalent of dew. Surface hoar grows most often when the wind is calm or light on cold relatively clear nights. These crystals can also grow during the day on shady slopes. Once buried, layers of surface hoar are slow to gain strength, sometimes persisting for a month or more as potential failure planes for slab avalanches.
Probability of Surviving an Avalanche
Survival refers to the actions of individuals caught in an avalanche. Self-rescue refers to the actions taken by fellow group members if an individual is buried.
Experience and statistics show that fully buried avalanche victims who are still alive when the avalanche stops moving must be found and dug out quickly (within 15 minutes) to have reasonable chances of survival. In Canada, the chance of an organized professional rescue team arriving in that time frame are poor unless the accident happens in an area where an avalanche safety program operates. Even in such areas, alerting a team and mounting an organized rescue may take some time.
In light of this, the efforts of the people who survive and/or witness an accident are crucial to the survival of victims. If the self rescue fails to find buried victims. it is likely that organized rescue teams will arrive too late to make a live recovery.
Self rescue techniques must be planned and practiced so the response of people on site is fast and efficient.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Diagram from "Avalanche Safety Course Overheads" Copyright © 1998 Canadian Avalanche Association
Surface Deposits and Crusts is a category that includes sun crust, wind crust, rain crust, rime and other melt / freeze crusts.
Rime is the deposition of super-cooled water droplets on any object. It may build up into the wind on days when there is an "ice fog" of super cooled water droplets in the air.
Firnspiegel is a thin, often highly reflective, type of sun crust formed by solar radiation on cold clear days. It acts like a "greenhouse" to enhance melting just below the surface. It may even appear to be suspended above the rest of the snow surface by a millimetre or more.
Chart from "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 1995 Canadian Avalanche Association
The temperature gradient is the most important factor determining the type of metamorphism, the resulting grain form, and the rate of growth of the grains,
Temperature Gradient is the difference in snow temperature across a given vertical distance in the snowpack. In practice it is expressed in degrees Celsius per 10 centimetres. As a general rule, a temperature gradient less than 1 degree / 10cm is considered weak. A strong temperature gradient is greater than 1 degree / 10cm. Strong Temperature gradients promote greater vapour movement than weak gradients.
The nature of the temperature gradient influences the type of metamorphic process that will be dominant in a given portion of the snowpack. The primary processes are faceting and rounding.
Faceting and rounding take place in the snowpack interchangeably. When the temperature gradient is strong and the snow density is low, the faceting process dominates. When the temperature gradient shifts from strong to weak (usually the result of warming at the snow surface), faceted grains, depth hoar and surface hoar grains begin rounding. These large angular grains resist rounding much more than branched new snow crystals and may remain weak for long periods.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
(For an explanation of the graphical symbols drawn in the following diagrams within each layer to denote snow grain type see Classification of Snow Crystals.) The cross section of a snowpack at left shows a strong temperature gradient. The height of the snowpack is 100cm and the snow temperature near the top of the snowpack is -15 degrees C. This creates an "average" temperature gradient within this snowpack of 1.5 degrees / 10cm. The actual gradient in any particular layer varies and may be greater or less than this average, but it can be expected that in this sample snowpack the faceting process will be predominating. (This process has gone by other names including temperature gradient metamorphism, TG metamorphism, Constructive metamorphism, recrystallization and kinetic growth. The term faceting is preferred.) This example is fairly typical of a snowpack that you may find in early winter in many regions or in the Canadian Rockies even during mid-winter or later. If this temperature gradient does not change, the snowpack will continue to lose strength over time and a base of weak depth hoar will continue to develop. Faceted grains and depth hoar formed in this way will persist in the snowpack and can cause cycles of avalanche activity for the rest of the winter and even into the spring or, in some cases, summer. Weak Temperature Gradient The cross section of a snowpack at left shows a weak temperature gradient. The height of the snowpack is 200cm and the snow temperature near the top of the snowpack is -15 degrees C. This creates an "average" temperature gradient within this snowpack of 0.75 degrees / 10cm. The actual gradient in any particular layer varies and may be greater or less than this average, but it can be expected that in this sample snowpack the rounding process will be predominating. (The rounding process has gone by other names including equi-temperature metamorphism, ET metamorphism, destructive metamorphism, and equilibrium growth. The term rounding is preferred.) In this sample snowpack, the temperature gradient is weaker near the base and stronger near the top. There is no place in this sample snowpack that the faceting process will be predominating. This example is fairly typical of a snowpack that you may find in early winter in a deep snowpack region with moderate climate (such as the Coast Ranges of British Columbia or the US). Similarly this type of snowpack may exist in the Columbia Mountains in the Interior of British Columbia in early winter during a heavy snowfall winter and certainly by mid winter in an average winter. The Canadian Rockies would typically only have this type of condition later in winter or spring or in a good snow year. If this temperature gradient does not change, the snowpack will continue to gain strength over time and any base of weaker facets as shown in this example will continue to strengthen. Even with a weak temperature gradient which promotes rounding and strengthening of the snowpack, hidden weak layers may exist. In this sample snowpack, a layer of surface hoar is buried just above 130cm. Buried surface hoar may persist in the snowpack and can cause cycles of avalanche activity for the next several weeks or more. The weak temperature gradient will eventually round out the surface hoar and promote bonding with the layers above and below but this gain in strength of this insidious layer can take a very long time in some cases. Text by Cyril Shokoples / Diagrams from "Avalanche Safety Course Overheads" Copyright © 1998 Canadian Avalanche Association
A terrain feature that increases the consequences of getting caught in an avalanche. For example, gullies and crevasses increase the odds of a deep burial, and cliffs increase the odds of traumatic injuries.
Shovel Shear Test, Compression Test, Rutschblock Test
The information presented below is intended to provide familiarity with these test, but in no way is it intended to be a guideline for precisely how, when or where these test are employed or how they are definitively interpreted. For proper technical standards for conducting these tests please refer to "Observation Guidelines and recording Standards for Weather, Snowpack and Avalanches" Copyright © 1995 Canadian Avalanche Association. For training in proper application of these tests in the field, consult an avalanche professional or attend a recognized training course.
We should be very careful with interpreting slope tests since they overestimate the slope stability at least 10% of the time. (Jamieson, 2000)
The tests described here are those which require very little equipment besides a shovel, knotted cord and possibly a snow saw. The tilt board and shear frame tests are not described here as they are seldom (if ever) used by recreational travelers. The tests described are:
Shovel Shear Test
Compression Test
Rutschblock Test
The grid method of transceiver search has now largely been replaced by the Induction-line method discussed above. Grid searching is usually slower and requires the searcher to cover more terrain before being able to pinpoint the final location. Variations of the technique below have been devised to reduce search times.
Once you have picked up a signal, you begin by carefully scanning to find the direction in which the signal is strongest. You mark the point at which the signal is received and quickly move in the direction of the strongest signal along a straight line. If the signal immediately gets weaker, consider moving the opposite direction instead. As you travel, monitor the signal strength / volume and if the signal gets increasingly loud, turn the signal down until it is just barely audible. Continue to walk in the same line until the signal fades. mark this point again. Move back along the direction of travel you just came on and find the spot along this line with the strongest signal.
From the point with the strongest signal make a 90 degree turn and quickly walk in a straight line. If the signal rapidly fades mark that spot and go the opposite direction. You should notice the signal increasing in strength. Go past this point until it fades again. Mark this point and retrace your steps until you find the loudest signal. Turn the signal down until it is barely audible again. Make a 90 degree turn and repeat the process of locating the fade points and going to the centre of the line to change direction.
Repeat this procedure until you have turned down the control to the lowest possible setting. At this point you should be ready to begin pinpointing and you should be getting people ready to probe and dig almost immediately.
Diagram from "Avalanche Safety Course Overheads" Copyright © 1998 Canadian Avalanche Association
Induction-Line Transceiver Search Technique
A number of years ago all manufacturers of avalanche transceivers agreed to manufacture only transceivers that transmitted and received on a frequency of 457 kiloHertz (or 457 kHz). One of the benefits of using this frequency is that it allowed a new and faster technique for searching to be employed. (Up until that time transceiver searches were conducted using an older and usually much slower technique called the "grid - search technique".)
Learning the Induction
While the initial search is carried out, an organized transceiver search is set up. Transceiver searchers are used when it is known that victims are wearing transceivers or if it is uncertain whether transceivers were used.
If victims are not found using these primary steps, secondary search procedures are implemented.
Text from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Single Searcher on a Small Slide
Depending upon the size of the avalanche debris and the number of searchers available, various search patterns may be used in deploying searchers. If the slide path and avalanche debris is confined in a narrow area (typically less than 40 metres wide) a single searcher can search by moving down the slide path and onto the debris in a straight line in the middle of the slope.
Single Searcher on a Large Slide
If there is only a single searcher and the slide path and debris covers a larger area, the searcher must zigzag down the slope, all the while ensuring that they never get more than about 20 metres away from the last track that they searched along. If the spacing between the zigzags is too large, the signal may be missed and the search will have to be started again, wasting valuable time.
Several Searchers on a Small Slide
If there are several people searching on a smaller avalanche, the searchers can line up along the top of the slope and space themselves out evenly. The searchers should not be more than about 20 metres apart. They proceed directly down the slide path until a signal is heard.
Several Searchers on a Large Slide
If the slide path is large and the group size is not sufficient to allow reasonable spacing between group members, then a combination of the two techniques just discussed may be required.
Diagrams from "Avalanche Safety Course Overheads" Copyright © 1998 Canadian Avalanche Association
Since weather maps and charts often display the time in UTC or "zulu" time, this chart will allow you to convert UTC / zulu time to your local time. On weather charts, UTC time is often abbreviated or written in several ways, for example 12 noon UTC time may be written 1200Z or sometimes simply 12Z. Notice that since some provinces change back and forth between daylight savings time, there are both summer and winter conversion charts.
Winter
| UTC (or Zulu) | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 | 1800 | 1900 | 2000 | 2100 | 2200 | 2300 |
| Newfoundland | 2030 | 2130 | 2230 | 2330 | 0030 | 0130 | 0230 | 0330 | 0430 | 0530 | 0630 | 0730 | 0830 | 0930 | 1030 | 1130 | 1230 | 1330 | 1430 | 1530 | 1630 | 1730 | 1830 | 1930 |
| Atlantic | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 | 1800 | 1900 |
| Eastern | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 | 1800 |
| Central | 1800 | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 |
| Saskatchewan | 1800 | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 |
| Mountain | 1700 | 1800 | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 |
| Pacific | 1600 | 1700 | 1800 | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 |
Summer
| UTC (or Zulu) | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 | 1800 | 1900 | 2000 | 2100 | 2200 | 2300 |
| Newfoundland | 2130 | 2230 | 2330 | 0030 | 0130 | 0230 | 0330 | 0430 | 0530 | 0630 | 0730 | 0830 | 0930 | 1030 | 1130 | 1230 | 1330 | 1430 | 1530 | 1630 | 1730 | 1830 | 1930 | 2030 |
| Atlantic | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 | 1800 | 1900 | 2000 |
| Eastern | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 | 1800 | 1900 |
| Central | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 | 1800 |
| Saskatchewan | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 | 1800 |
| Mountain | 1800 | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 | 1700 |
| Pacific | 1700 | 1800 | 1900 | 2000 | 2100 | 2200 | 2300 | 0000 | 0100 | 0200 | 0300 | 0400 | 0500 | 0600 | 0700 | 0800 | 0900 | 1000 | 1100 | 1200 | 1300 | 1400 | 1500 | 1600 |
Digging for a victim is tiring and often takes longer than the search, so it is important to be as efficient as possible. Here are some tips that make the recovery process easier and faster.
If the victim is deeply buried, begin digging well away from the probe. As a rule of thumb, the hole required to expose the victim will be at least the square of the depth (that is, if a victim is buried 2 metres deep, the hole required will be at least 2m by 2m).
Dig on the downhill side of the probe and throw snow downhill.
Too many people get in each others way and hamper efficient digging.
Diggers should be rotated often (every few minutes if possible). As soon as one begins to tire or slow down someone fresh should take over.
Deep holes may require tiers with diggers on each tier moving snow from the bottom to the surface.
When the victim is found, uncover the head and chest immediately, clear the mouth and airway, and begin first aid while the rest of the victim's body is uncovered.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Fronts
A front is the interface between two air masses with differing characteristics. For example, a cold, dry air mass and a warmer, wetter one.
Cold Front
If a cold air mass is advancing and pushing against a warm one the front is called a cold front.
Warm Front
If a warm air mass is advancing and pushing against a cold one the front is called a warm front.
Quasi-Stationary Front
If neither air mass is advancing the front is called a quasi-stationary front.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
At warms fronts, as the lighter warm air advances, it is lifted and it rides up over the heavier, colder air. Warm fronts usually move more slowly than cold fronts and the slope of the overriding air is very shallow. Thus the vertical velocities associated with lift at warm fronts are much less than at a cold front, but the lifting occurs over a much wider area. If the warm air is sufficiently moist, clouds form and precipitation results. The precipitation may be less intense but is often of longer duration than that associated with cold fronts.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
Frontal waves form at the earth's surface at a point along a stationary front. When the wind flow is in opposite directions along the front, a bend forms where cold air begins to displace warm air, forcing the warm air upwards. Under the right conditions, this displacement continues and develops into a wave-like kink that moves along the frontal boundary.
In a developing wave, the cold air in the trailing section of the wave moves faster than the leading section of warm air. As the heavier cold air catches up it pushes under the lighter, warm air, lifting a parcel of warmer air aloft (out of contact with the ground). This forms what is known as an occluded front, or a TROWAL (acronym for TRough Of Warm Air aLoft).
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The sound of a fracture propagating along a weak layer within the snowpack. Whumpfs are indicators of local instability. In terrain steep enough to avalanche, whumpfs usually result in slab avalanches.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
The wind exposure of slopes is a primary factor in avalanche formation.
Lee (downwind) slopes are more likely to produce avalanches than are other slopes with equal incline because they receive much greater accumulations of dense, slabby snow. Lee slopes are found behind high ridges, fall line ribs, rows of trees, hills, convex parts of slopes, and gully walls.
Snow on slopes exposed to the wind (windward) is often shallow and/or irregular due to scouring, creating a potential weak snowpack.
While local wind is significant, it is important to remember that ridge-top wind speed and direction may be quite different from winds experienced locally.
Text and diagram from "Advanced Avalanche Safety Course Manual" Copyright © 1998 Canadian Avalanche Association
One or more stiff layers of wind deposited snow. Wind slabs usually consist of snow crystals broken into small particles by the wind and packed together.
There are no definitions in this section.
There are no definitions in this section.
There are no definitions in this section.
