Action of Victims on Foot (Skis, Snowboard, Snowshoes) Or Snowmobile Actions You Should Take If Caught If Caught in an Avalanche

Action of Victims on Foot (Skis, Snowboard, Snowshoes) or Snowmobile

Actions You Should Take if Caught

If caught in an avalanche:

• Call out for attention • Try to quickly exit to the side • Discard equipment (skis, poles, snowboard, snowshoes) • Try to grab trees and rocks • Kick, swim and fight to stay on the surface • Remember the terrain, be prepared for falls over cliffs, collisions with trees, and the stop in the runout zone

If caught by a powder avalanche:

• Seek shelter behind rocks, trees, vehicles • Crouch low and turn away from the avalanche • Cover nose and mouth • Brace against impact, hold onto trees, etc.

As the avalanche slows:

• Thrust and kick to the surface just before the snow comes to a complete stop • Pull hands and arms to the face and make an air space • Thrust an arm toward the surface

When the avalanche has stopped:

• Try to dig yourself out • Call when rescuers are near • Stay calm

Action of Victims Caught inside a Vehicle

Actions You Should Take if Caught

• If you are in a vehicle: • Turn off the engine • Do not smoke or use matches • Open window and check for depth of burial (for example, with a probe) • Do not leave the vehicle unless you are sure it is safe to do so or you are in a remote location • If you have a two - way radio, keep it turned on and call for help

Avalanche Cycle

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

Avalanches: Loose Snow

Loose avalanches are usually confined to surface layers, and therefore are often small. Loose snow avalanches:

• start from a point • gather mass progressively in a fan-like shape • require loose cohesionless snow • may contain dry or wet snow

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".

Avalanche Motion - Gliding Motion

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.

• may contain dry or wet snow

Avalanche Motion - Dry Flowing Motion

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

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.

Avalanche Motion - Wet Flowing Motion

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.

Avalanche Paths

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.)

Avalanche Size Classification (Canada)

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.

Avalanches: Slab

Large Hazardous avalanches are usually slab avalanches. Slab Avalanches:

• leave a fracture line • can release simultaneously over a large area, setting large volumes of snow into motion • may start as a shallow surface layer • may consist of a thicker layer(s) deeper in the snowpack • may involve a number of layers • range from new snow (soft slab) to hard wind - packed snow (hard slab) • may contain dry or wet snow

Avalanche Tracks, Characteristics of

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 avalanches 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.

Avalanche Transceiver

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. B

Bed Surface

The surface on which an avalanche runs. Not to be confused with failure plane. C

Cloud Cover Codes

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.

Compression (Shovel) Test

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:

• Very Easy (CV) - fails during cutting of column • Easy (CE) - fails with 5 - 10 light taps using finger tips only • Moderated (CM) - fails with 5 - 10 moderate taps from elbow using finger tips • Hard - (CH) - fails with 5 - 10 firm taps from whole arm using palm or first • Collapse (SC) - block settles when cut

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

Common Trigger Points

Convection and Convective Lifting

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.

Cornice

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.

Cross - Loaded

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.

Depth Hoar

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. E

Effect of Ground Roughness and Forests

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.

Effect of Exposure to Sun

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.

Faceting

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:

• A strong temperature gradient, generally greater than 1 degree / 10cm (which quickly drives water vapour from warm areas to cold) • Loose, low density snow (which facilitates the free movement of water vapour between grains) • Presence of crusts (which concentrate water vapour, promoting vapour transfer in the concentrated area) • Moderate snow temperature (which maximizes the amount of vapour the snowpack can hold but does not reduce the overall temperature gradient significantly)

Failure of a Snow Slab

For a slab avalanche to start, there must be:

• A cohesive, relatively strong layer • A stronger layer overlying a weak layer or a weak bond between layers • A closely balanced stress - strength relationship between the weak layer and the overlying snow • A trigger which upsets the balance (Triggers may be natural factors, such as: heavy snowfall, rapid depositing of snow by wind, a rapid rise in temperature, fall of a cornice, ice fall, earthquake. Triggers may also be artificial factors such as: skiers, snowboarders, snowshoers, snowmobiles, hikers, vibrations from machinery and traffic, and explosives.) • A mechanical condition that allows the condition to propagate (spread). Hard snow allows wide propagation and tends to produce large slab avalanches.

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:

• an initial shear or tension failure occurs. • Failure then propagates along a shear plane (usually the weak layer) to a location where the snow is under tension (convex roll, rock outcrop, etc.) • A tension failure occurs when the tensile strength of the slab is exceeded. • The fracture line forms. (Due to propagation, the point of initial failure may be a considerable distance from the fracture.)

Fracture Lines and Trigger Points

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.

Failure Plane

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. G

Global Circulation

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.

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".

High and Low Pressure

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.

High - Marking

(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. I

The Initial Search

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.

• Do a visual search for clues on the surface (that is, hand, foot, clothing, and equipment). • Call out occasionally and listen for responses from victims. • Pull any items found out on the snow to see if a victim is attached. • Mark the location of found items and bring them to the attention of the rescue leader. • Listen carefully for transceiver signals in these locations. (If victims were not wearing transceivers or if is unknown. whether transceivers were used, quickly probe the area around found items.) • If a transceiver signal is found, carry out a transceiver search. If there is more than one person buried, the initial search continues to look for visual clues, etc. • Probe likely burial areas.

Lifting of Air Masses

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:

• Upslope Lift is produced when air gradually rises in altitude as it moves over a gently rising landmass. For example the rise from East to West across the prairies of western Canada. The eastern side of the Rockies may get considerable snowfalls during upslope conditions when there is a deep low in the mid-mountain area of the USA and the upper end of the system is in southern Alberta. The counterclockwise circulation around the low creates upslope lift in southern Alberta which is intensified by orographic lift in the eastern slopes of the Rockies. • 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.. • Frontal Lift - for a detailed discussion of fronts see the page on Weather Fronts. • Lifting at a TROWAL - for a complete discussion of TROWALs see the page on Weather Fronts. • Convergence means the "piling up" of air above some location. If air converges at or near the surface, some of it is lifted upwards. Conversely, diverging air from a high pressure centre near the surface tends to subside, becoming warmer and drier. - for additional discussion of convergence and divergence see the page on Barometric Pressure.

Metamorphism of Snow

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. 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.

Melt-Freeze Metamorphism

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.

Occluded Front (forming TROWAL)

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).

Organized Rescue

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.

Organizing a Self-Rescue

Rescue by Survivors

If you survive, witness, or come upon an avalanche accident there are four primary stages that must be carried out immediately:

1. Organizing the rescue 2. Initial Search 3. Transceiver Search 4. Pinpoint and Recovery

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.

• If necessary, establish a spotter to watch for further avalanches and establish a warning signal and escape routes should another avalanche occur. • Determine how many people are missing. • Mark the "last seen point" if practical. • Determine likely burial areas (for example, around trees, rocks, roads, and in the flow line down from the "last seen point". • Organize people to carry out the following tasks: o call for help (if radio, cell phone, or other immediate means of communication are available) o prepare rescue equipment (1st aid kit, probes, shovels, etc.) o carry out an initial search o Carry out a transceiver search o Ensure everyone has transceivers turned to receive.

Orographic Lifting

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.

Pinpoint and Recovery

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:

• Particularly if using transceivers with loudspeakers, only one person should home in and pinpoint the signal. • When homing in on the victims location, move as quickly as possible and turn the volume of your transceiver down whenever possible. • When pinpointing the final location, use a logical pattern and slow down so as not to miss the strongest point. • Mark the area where the signal is strongest. • Probe the marked area using a logical pattern. • When the victim is hit with the probe, DO NOT REMOVE THE PROBE. • Notify the rescue leader of the hit. • Note the approximate depth of the victim. • Begin rescue digging.

Precipitation Particles, Sub-classification of

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.

• Columns are new snow crystals consisting of a six - sided hollow or solid prism. A capped column has flat plates attached to the ends. • Needles are thin, long, needle - like crystals of new snow. • Plates are thin, plate - like, usually hexagonal crystals of new snow. Layers of plates can form a failure plane for an avalanche as the plates may not bond well to one another. Plate crystals become rounded slowly and may form weak layers for long periods of time. • Stellar crystals are what many people commonly think the classic snowflake should look like in that they are star - like new snow crystals with unbroken arms. Dendrites are star - like new snow crystals with numerous side branches, often three - dimensional. • Irregular Crystals are those which defy categorization into the other classes or sub - classes. • Graupel is formed when a snow crystal falls through a layer of air that is supersaturated with moisture. As the crystal falls through the air the water droplets instantly freeze onto the crystal surface forming miniature dull colored balls of "rime". As the rime continues to accumulate on the crystal, its original shape becomes obscured and is no longer recognizable. The grain now simply looks like a dull colored tiny ball of snow. • Hail forms when a precipitation particle falls through a layer of moist air and becomes coated with a layer of ice. Convective winds then blow the precipitation particle back up into the cloud where it falls through the moist air again and grows in size with an additional layer (s). This process may continue through several cycles. Hail particles exhibit a layered or laminated internal structure when carefully sliced open. In essence, hail is a ball of ice whose size has increased by added successive layers of ice on the outside. • Ice Pellets may form when rain falls though a very cold air mass. As a result the rain drops may freeze into pellets. Other processes may form pellets as well.

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

Pressure, High and Low

Probe Lines - 3 Holes per Step

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:

• Establish the most likely area of burial. • Line up searchers in a straight line, spaced approximately 1.5 metres apart (wrist to wrist). • Searchers probe three times, once in front of the sternum, then reaching left and right about 50 cm on either side of the middle hole. • Searchers take one step forward (~70cm) and repeat the process.

Probe Lines - Coarse Probe

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.

Probe Lines - Fine Probe

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.

Propagation

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. R

Rescue by Survivors

If you survive, witness, or come upon an avalanche accident there are four primary stages that must be carried out immediately:

1. Organizing the rescue 2. Initial Search 3. Transceiver search 4. Pinpoint and recovery

If victims are not found using these steps, secondary search procedures are implemented.

Rime

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.

Rounding

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:

1. In the initial stage of rounding, the sharp ends of new crystals and the points of faceted grains sublimate and the resulting water vapour is deposited in concave areas. At high temperatures, molecules also glide along the grain surface from convexities to concavities. As well, large grains with broad curvatures grow at the expense of small grains with sharp curvatures. The result is a concentration of mass with a minimum surface area. 2. Under weak temperature gradients, water vapour moves from warm areas to cold, but the rate of movement is much slower than in strong temperature gradient environments. Slow moving vapour is deposited on the colder surfaces in a more homogenous manner and the faceted, stepped pattern associated with a strong temperature gradient does not occur.

The following conditions promote rounding:

• A weak temperature gradient generally less than 1 degree C per 10 cm (which moves water vapour slowly from warm areas to cold) • Dense, tightly packed snow • Small grains (which produce denser snow) • A high snow temperature, typically above -10 degrees C (which promotes weaker temperature gradients)

Rutschblock Test

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.

Avalanche Search and Self - Rescue

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

• Organizing the Search • Initial Search • Transceiver Search • Pinpoint and Recovery o Induction Technique o Final Pinpoint Search o Grid Technique • Secondary Search o Use of Avalanche Probes

Self Rescue on Roads

Organized Rescue

Secondary Search

Secondary Search Procedures

If a transceiver search is unsuccessful, secondary procedures must be used:

• Continue with initial search procedures. • Probe around likely burial areas (for example, around trees, around rocks, on benches, in gullies, in deep deposits) in the victim's known or suspected line of travel. • If probing around found items or in likely areas of burial is unsuccessful, an organized probe line may be useful if there are enough searchers to set one up. (A probe line needs at least 6 searchers to be efficient. If there are not enough searchers, continue with probing of likely areas.) • Coarse probe likely areas of burial. • Mark probed areas. • Consider going for help: o safety of those going out o how many will be left to continue searching o time before rescues arrive o survival chances of victim in that time • If going for help, note the following information: o exact location of the accident o access (road, trail, helicopter) o time of accident o weather and snow conditions o number of people buried o rescuers on site • Continue searching, but make provisions for feeding, sheltering, and safety of searchers is an extended search is anticipated.

Self Rescue on Roads

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:

• Stop in a safe location. • Direct vehicles and people to a safe area. • Check dimensions of avalanche and determine whether vehicles could be caught in it. • Before carrying out any rescue procedures, carefully assess the potential for further avalanches. (Remember, you do not have as much information as you might in a backcountry situation.) • Unless you are reasonably sure the situation is safe and that people are in the avalanche, send for help and wait for assistance.

Shovel Shear Test

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:

• Very Easy (SV) - fails during cutting or insertion of shovel • Easy (SE) - fails with minimum pressure • Moderated (SM) - fails with moderate pressure • Hard - (SH) - fails with firm sustained pressure • Collapse (SC) - block settles when cut 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.

Sintering

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.

Size 1 Avalanches Size 1 avalanches are relatively harmless to people. They typically have:

• a mass of 10 tonnes • a path length of 10 metres • an impact pressure of 1 kiloPascal

Size 2 Avalanches

Size 2 avalanches could bury, injure or kill a person. They typically have:

• a mass of 100 tonnes • a path length of 100 metres • an impact pressure of 10 kiloPascals

Size 3 Avalanches

Size 3 avalanches could bury and destroy a car, damage a truck, destroy a small building, or break a few trees. They typically have:

• a mass of 1000 tonnes • a path length of 1000 metres • an impact pressure of 100 kiloPascals

Size 4 Avalanches

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:

• a mass of 10,000 tonnes • a path length of 2000 metres • an impact pressure of 500 kiloPascals

Size 5 Avalanches

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: • a mass of 100,000 tonnes • a path length of 3000 metres • an impact pressure of 100 kiloPascals

Slab

One or more cohesive layers of snow that may start to slide together.

Sluff

A small avalanche usually made up of loose snow.

Slope Incline and Avalanche Frequency

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)

Snow Crystals, General Classification of

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:

• Precipitation Particles are any freshly fallen "new snow" type. This can include a wide variety of specific forms that are sub - classified. 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. • Decomposing and fragmented Particles are those snow crystals that have in some way been changed from their original form. This change can be through mechanical action (such as with wind) or through natural processes such as rounding (in which a crystal loses its original form and branches of a crystal can become detached from the original crystal). Parts of the original crystal forms may still be discernible. Decomposing forms are often smaller than the original particles from which they formed. • Rounded Grains are those in which the original form is no longer discernible and the crystal takes on a generally rounded amorphous appearance. Rounded grains typically tend to be smaller grains and are usually significantly smaller than the original grain from which they formed. Typical grain size is often less than 1mm. Commonly referred to as "rounds" these grains tend to be found in harder or stronger snowpack layers. Rounded grains typically form when there is a weak temperature gradient in the snowpack (<1 degree / 10 cm). This weak temperature gradient occurs most often in areas where the snowpack is deep and temperatures are mild. • Solid Faceted Crystals are those in which the original crystal form is often no longer discernible and the crystals begin to take on an angular, faceted or striated appearance with straight edges and angular corners beginning to predominate. Faceted grains typically tend to be larger grains and are often significantly larger than the grain from which they formed. Typical grain size is often more than 1mm. Commonly referred to as "facets" or "sugar snow" these grains tend to be found in softer or weaker snowpack layers. Faceted grains typically form when there is a strong temperature gradient in the snowpack (>1 degree / 10 cm). This strong temperature gradient occurs most often in areas where the snowpack is shallow and temperatures are cold. According to Avalanche Accidents in Canada (Geldsetzer and Jamieson), faceted grains and surface hoar are the weak layer in the failure plane in 78% of fatal accidents. These crystals have poor bonds with each other or adjacent layers and persist in the snowpack for a long time until there is adequate load to make them fail. • Cup Shaped Crystals (Depth Hoar) are those in which a faceted form continues to grow or mature in the presence of a strong temperature gradient. These crystals are heavily striated and can have cup or scroll shapes. The grains typically tend to be very large and are often significantly larger than most other grains that would be found in a snowpack. Typical grain size can be more than 3 - 5mm. Commonly referred to as "depth hoar" or "sugar snow" these grains tend to be found in very soft or very weak snowpack layers usually near the bottom of a weak, shallow snowpack. Depth Hoar forms when there is a strong temperature gradient in the snowpack for a protracted period of time (>1 degree / 10 cm). This strong temperature gradient occurs most often in areas where the snowpack is shallow and temperatures are moderate or cold. According to Avalanche Accidents in Canada (Geldsetzer and Jamieson), faceted grains and surface hoar are the weak layer in the failure plane of slab avalanches in 78% of fatal accidents. Depth Hoar crystals have very poor bonds with each other or adjacent layers and can persist in the snowpack until the end of winter or until there is adequate load to make them fail. These grains can be the weakness in avalanches that fail right at the ground, in which the entire winter snowpack is involved in a large climax type of avalanche. • Wet Grains are just as the name implies... WET. They form when temperatures are above freezing, when solar radiation is intense, when rain falls onto the snowpack or when any of these factors occurs individually or together. The original crystal shape is often rapidly changed and rounded. While grains are warm and wet they tend to be weak and can fail in wet loose avalanches or wet slab avalanches. • Feathery Crystals (Surface Hoar) form on the surface of the snow under conditions where there is a generally clear sky with high humidity and little or no wind. These crystals are the same as the "hoar frost" seen sparkling on trees and on the snow surface after a clear cold night. They can be large in size (>10mm) or smaller (<1mm). As a broad generalization, the larger the size of surface hoar the more likely that it will form a poor bond to the adjacent snow layer. Once buried under a new snow layer they can be difficult to detect without diligent testing. According to Avalanche Accidents in Canada (Geldsetzer and Jamieson), faceted grains and surface hoar are the weak layer in the failure plane in 78% of fatal accidents. These crystals have poor bonds with each other or adjacent layers and persist in the snowpack for a long time until there is adequate load to make them fail. • Ice Masses often form when a wet layer cools and hardens. • Surface Deposits and Crusts is a broad category that includes sun crust, wind crust, rain crust, rime and other melt / freeze crusts. This can include a variety of specific forms that are sub - classified.

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

Stepped Down

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.

Storm Snow

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.

Subsidence and Convergence 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.

Sun Crust

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.

Surface Hoar

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.

Avalanche Survival

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.

The Temperature Gradient

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 shits 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.

(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.)

Strong Temperature Gradient

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.

Terrain Trap

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.

The Temperature Gradient

Standard Tests

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

Transceiver Search - Grid Pattern Method

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.

Transceiver Search - Induction Technique

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-line technique is a practical skill and it should be practiced several times a season or, better still, at the beginning of each outing. It cannot be learned from this description alone. In addition, at the beginning of each trip and at critical points thereafter, avalanche transceivers should be checked to ensure adequate transmit and receive range as well as to ensure that the batteries have not died.

The basis of the induction-line technique is that an avalanche transceiver actually has an electromagnetic field that surrounds it each time the transceiver transmits. The field has a three dimensional shape somewhat like an apple and can be seen represented (two - dimensionally) in the diagram at left.

Using a transceiver in receive mode, the searcher moves or orients his / her transceiver up until it is along one of the "flux lines" shown. That "flux line" is then followed like a railroad track curving into a station. (Of course, the flux lines are not actually visible, but in effect you do follow an induction - line or flux line, thus the name of the technique.)

Once you have picked up a signal, you begin by carefully scanning to find the direction in which the signal is strongest. You now quickly move in that direction for a distance of about 5 metres. (If the signal immediately gets weaker, consider moving the opposite direction instead.) You always want to travel in the direction that makes the signal stronger or sound louder. On beacons with visual indicators you want more lights or bars illuminated on an LED or LCD display.

At this point you pause and scan again, moving the transceiver in about 15 degree increments waiting for a signal in between each move so that you can decide which is the strongest direction. Once you have decided the direction in which the signal is strongest, you should see if you can turn down the "distance" or "sensitivity" setting on your transceiver.

If you have a beacon that has a speaker (or earphone) and no lights, turn the volume down so that you can just barely hear the signal each time you stop. If you have a beacon with lights, you should follow the manufacturers directions for when to turn down the setting. (Some newer digital beacons do not have settings that require changing.)

Quickly move in the direction of the strongest signal again for a distance of about 5 metres. Pause and scan again, moving the transceiver in about 15 degree increments. Find the strongest signal and turn down the setting again if required. 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.

An advanced version of the Induction-line technique has the person stop to reorient the beacon after moving 10 percent of the distance setting currently set on the transceiver. For example, if the setting you are on is the 80 metre range, the distance you move is 8 metres. If the setting you are on is the 15 metre range, you only move a distance of 1.5 metres before scanning again. This adaptation has the advantage of recognizing that you will likely have to turn more often and more dramatically the closer you get to the buried subject. In addition you are less likely to move too far and walk past the subject using this modification.

Some digital beacons actually give a distance reading for how far you are from the subject and/or lights that direct you which way you should turn to find the best signal. (The distance shown is not the actual distance but rather the distance along the "flux line".) Advances in beacon technology have been dramatic in the last decade. Future beacons may be even better.

Transceiver Search

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.

• In small avalanches, or if limited numbers of rescuers are available, it may be possible to combine an initial and transceiver search in one operation. • If it is known that victims are not wearing transceivers, the transceiver search is not required or useful. Rescuers not involved in the initial search should be used to set up secondary search procedures. • Transceiver searchers need only a transceiver but probes, shovels, and other equipment should be readily available. • The rescue leader determines a search pattern that ensures the entire area where burials are likely will be covered. Some overlap should be included to ensure a signal will not be missed by searchers. • Searchers are sent on the slope and directed in the pattern. • Searchers listen for signals and look for clues on the surface. • If a signal is heard it should be brought to the attention of the rescue leader immediately and the most experienced searcher who is readily available should begin to home in on the signal. • Using an induction-line or grid search technique, home in on the transceiver signal until the lowest receive setting is being used. • Pinpoint the signal and recover the victim. If victims are not found using these primary steps, secondary search procedures are implemented.

Search Patterns

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.

UTC Conversion Charts

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 0600070008000900100011001200130014001500160017001800 1900 2000 2100 22002300

Newfoundland 2030 2130 2230 2330 0030 0130 0230033004300530063007300830093010301130123013301430 1530 1630 1730 18301930

Atlantic 2000 2100 2200 2300 0000 0100 0200030004000500060007000800090010001100120013001400 1500 1600 1700 18001900

Eastern 1900 2000 2100 2200 2300 0000 0100020003000400050006000700080009001000110012001300 1400 1500 1600 17001800

Central 1800 1900 2000 2100 2200 2300 0000010002000300040005000600070008000900100011001200 1300 1400 1500 16001700

Saskatchewan 1800 1900 2000 2100 2200 2300 0000010002000300040005000600070008000900100011001200 1300 1400 1500 16001700 Mountain 1700 1800 1900 2000 2100 2200 2300000001000200030004000500060007000800090010001100 1200 1300 1400 15001600

Pacific 1600 1700 1800 1900 2000 2100 2200230000000100020003000400050006000700080009001000 1100 1200 1300 14001500

Summer

UTC (or Zulu) 0000 0100 0200 0300 0400 0500 0600070008000900100011001200130014001500160017001800 1900 2000 2100 22002300

Newfoundland 2130 2230 2330 0030 0130 0230 0330043005300630073008300930103011301230133014301530 1630 1730 1830 19302030

Atlantic 2100 2200 2300 0000 0100 0200 0300040005000600070008000900100011001200130014001500 1600 1700 1800 19002000

Eastern 2000 2100 2200 2300 0000 0100 0200030004000500060007000800090010001100120013001400 1500 1600 1700 18001900

Central 1900 2000 2100 2200 2300 0000 0100020003000400050006000700080009001000110012001300 1400 1500 1600 17001800

Saskatchewan 1900 2000 2100 2200 2300 0000 0100020003000400050006000700080009001000110012001300 1400 1500 1600 17001800

Mountain 1800 1900 2000 2100 2200 2300 0000010002000300040005000600070008000900100011001200 1300 1400 1500 16001700

Pacific 1700 1800 1900 2000 2100 2200 2300000001000200030004000500060007000800090010001100 1200 1300 1400 15001600

Weather Fronts

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.

Front Waves

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.

Whumpf

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.

Orientation to Wind - Loading & Lee Slopes

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.

Wind - Slab

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.