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Avalanche awareness

Avalanche training Guidelines

If you take an avalanche course, make sure it follows the guidelines of the American Avalanche Association (AAA), which requires at least 24 hours of instruction, 1/2 of which is in the field. Requirements for Class I instruction are on the web site. Make sure you get an instructor who has:

• Experience forecasting avalanches (such as for heli-skiing, for a resort, or for a highway authority).
• Seen lots and lots of avalanches (> 1000).

In Tahoe, classes are offered by Donner Summit Avalanche Seminars

Resources

Avalanche hotline: US forest service in Truckee 530 587-2158 or online at http://www.fs.fed.us/r5/tahoe/currentconditions/

Snow Characteristics

Snow has several characteristics which make it a weak material:

1. Snow looks like a single blanket, but it is made up of a series of layers. Every storm, and every cell within each storm, lays down a different layer. Horizontally driving snow is different from light snow that falls straight down. Avalanche likelihood is impacted by how well a layer of snow sticks to another layer of snow.
2. Snow is inherently weak.

   Snow consists mostly of air, held together by skeletal structures. The lightest champagne powder snow is 5-6% water. Sierra "powder" is 8-10% water. Sierra cement (or cascade concrete) is 12-15% water. Mixed rain/snow is 20% - 25% water. Snow exists at or near its melting point, around 0° C, and it is therefore not a stable structure. 0° C is the melting point, not the freezing point. Water is capable of freezing at 0° C, but only if it has an object that it can stick to, like a dust particle, the side of a rock, or frozen ice. A droplet of water suspended in the air (a cloud) will not spontaneously freeze until it is -40° C. Between -40° C and 0° C, water is in a supercooled state. Ice that is created between -40° C and 0° C is called rime ice. Rime ice is formed when supercooled water floats in and comes in contact with an object. Snow is infinitely variable in time and space. Snow will continue to change over time. Any material that is variable in thickness will break at its thinnest place. Terrain underneath snow can vary in height: Trees or rocks that stick up cause a thinner area of snow, which causes weakness. As a result, an avalanche often breaks from tree line to tree line.

3. Snow behaves in ways similar to a visco-elastic material like silly putty. It flows and stretches if pully slowly, but it can also break if pulled quickly. Snow on the side of a slope can stretch from the top to the bottom under the force of gravity, and then eventually break. The snowpack is like an inflated balloon. A force spread out over a large area will cause even deformation of the snow, which can be absorbed by the snowpack. A small force, like a skier, applied to a small area, can "pop" the snowpack and cause an avalanche. Every time you turn, you put 3-8 times your body weight on the snow.

Types of avalanches

1. Loose avalanche or point release avalanche: Starts at a point and becomes wider as it flows downhill, forming a triangle. It appears like a chain reaction, similar to sand falling down the side of a sand castle, and usually moves only the top 10cm of snow. Loose avalanches move slowly down the hill, and it is often possible to move out of the way. There are two types:

   Loose avalanches caused by dry snow: These usually do not cause injuries. Loose avalanches caused by very wet snow: They are somewhat more dangerous.

2. Slab avalanche: More dangerous than the loose avalanche. It is easy to predict and locate. In a slab avalanche, a large slab from the snow layer releases and slides downhill. The cross section at the top that remains after the slab avalanche at the fracture line is called the crown surface. The newly exposed slope revealed after the avalanche is called the bed surface. People usually trigger the slab avalanches that kill them. These avalanches have lots of mass, momentum, and inertia. Avalanches can approach 150-200 mph. A loose avalanche can trigger a slab avalanche.
3. Ice avalanche: resulting from falling ice flows. Ice avalanches are highly unpredictable, and do not correlate to snow, heat, weather, etc. It is best to avoid climbing on or under an ice flow. Not surprisingly, the most difficult segment of the Everest ascent is the Khumbu Icefall.
4. Cornice avalanche: Cornices are very weak when they are first formed, because the dry snow is barely held together by static electricity that results when the polar H2O molecules rub against each other. Cornices then get stronger over time, and then get weaker again as they melt. Cornice avalanches can trigger slab avalanches.
5. Roof avalanche: Created by snow on top of an artificial surface, with a heat source underneath. Roof avalanches are highly unpredictable, and can happen on any roof slope angle. Snow can melt at the surface from the underlying heat source, flow down the roof, and then freeze into solid ice at the eves where there is no heat. Roof avalanches have both snow and ice, and the falling ice can easily kill you, so it is best to stay away from under the eves.

Avalanche prediction

Avalanche forecasting is a mix of art and science. Leaning avalanche skills involves two things: Data measurement, and the human factor that influences how those measurements are interpreted. The data measuring aspect of avalanches consists of three main areas:

1. Terrain. The slope angle is the most important. 96% of all avalanches occur on slope angles between 30° and 45°. 50% of avalanches occur between 35° and 40°. You can avoid avalanches if you can avoid being on or underneath slope angles between 30° to 45°. The difference in risk between 28° and 30° is huge.
   
   If you have crampons, you can climb on slope angles above 45° with less risk, because snow sluffs off very quickly for angles of greater than 45°; however, you may be susceptible to an ice avalanche.
   
   Measure the slope angle using a clinometer. A transit can also be used. Clinometers are usually built into compasses. Manufacturers include:

   Suunto (M-3G and MC-2) Brunton (Classic, Elite and 8040 compasses) Silva (Ultra Ranger 530, Ranger 515CL and Ranger 515CLQ)

2. Weather. Weather aspects include wind loading:

   How fast the snow is falling in cm/hour The density of snow that is falling in % of water The length of time that the snow is falling

3. Snowpack. Weak layers in the snowpack increase avalanche risk. Slopes at different elevations have different layer characteristics.

In addition to these three measurable quantities, there is a 4th element, and that is the human factor. There are several issues related to the human factor:

1. The human factor which impacts how the measured quantities are interpreted. Humans are the only animal capable of going against logic, and one factor that can enter into avalanche prediction is rationalized expedience: A skier who wants or needs to traverse a terrain out of convenience may unwittingly skew his analysis to produce a prediction that is less risky.
2. The human factor that occurs after prediction. After avalanche risk is interpreted correctly, a skier may knowingly enter an area of high avalanche risk.
3. False asumptions. An example is assuming that someone else in the group is looking out for the safety of the group.
4. Presumed Safety. Just because someone else recently skied down a slope safely does not mean that the next person will ski down safely. Avalanches can be triggered by the 10th, 50th, or 100th person to ski down a slope.

Avalanche prediction can be simplified by reducing the data set that is used, and limiting the data that you are gathering. Not all data is important. A skier can limit data to the bullseye set of data, by observing mother nature's 5 billboards which advertise imminent avalanches:

1. Evidence of a recent avalanche. A recently avalanched slope indicates that slopes with the same characteristics (elevation, pitch, etc) are also likely to avalanche. An area of slope that is right next to a recently avalanched slope and of similar conditions is ripe for an avalanche.
2. Wumping sounds. The whole snowpack sinks by about 3 inches, causing a guttural reaction in skiers known as the sphincter factor. A weak layer of snow is collapsing, which causes the sheer strength between layers to be zero. The wump can travel all the way up to the top of a slope. Unfortunately, if you experience a wumping sound on a steep slope, an avalanche is imminent and likely to be upon you.
3. Hollow feeling/hollow sounds: It is like skiing on a 50 gallon drum. Snow piling in from a strong wind creates an airy layer, which can collapse underfoot.
4. Shooting cracks: A crack will lightning bolt to an anchor object like a tree.
5. Heavy windloading. Most avalanches occur within 24 hours of heavy precipitation. Avalanche likelihood increases significantly with 2cm/hour of accumulation, with a snow density of greater than 10%, for 5-6 hours, with 25 mph wind. If any of those factors increases, the likelihood increases.

After an avalanche path runs its course, the snowpack will not avalanche again at that location. If there are no possible avalanche release points above or to the side of the area, the avalanched area is considered safe.

Videotape highlights

Entertainment

Educational

• High-risk avalanches can occur on short slopes: most people are killed on smaller slopes of less than 300 feet.
• Skiers on a lower part of a slope can trigger an avalanche from above.
• Indicators of previous avalanches:
  • Sparse trees
  • Trees with no uphill branches
  • Uprooted trees lying down slope
  • Only saplings growing on the slope
• Lighter snow with strong winds can create heavy deposits on the leeward side of mountains.
• Rain often causes widespread avalanches, by percolating down and weakening layers of snow.
• Rapid rise in temperature gives rise to instability.
• Over time, bonds between layers of snow can strengthen or weaken.
• Feathery snow crystals create a weak layer.
• Snow stability can vary over small areas (50-100 feet).
• Melting snow that refreezes can create a hard surface for upper layers to slide.
• Danger signs:
  • Blocks of snow breaking up between skis
  • Hollow sound
• Stay clear of:
  • Narrow valleys - even a small avalanche can fill the valley with deep snow.
  • Cornices, on the top or bottom.
  • Bowls and valleys greater than 30° slope angle. At the bottom of a hill, walk around the potential runout of an avalanche.
  • Cliffs
• To minimize potential risk if you must ski down an avalanche prone slope:
  • Go one at a time
  • When traversing, stay in the same track
  • Pause only where rocks or trees offer protection
  • Stay to the edge of the slope
• Rescuing:
  • Probe the uphill side of trees and rocks, and where the snow is deepest.
  • Mark the last place the victim was seen, then search downhill from there.

Avalanche dynamics

If you are caught in an avalanche, the old conventional wisdom includes advice on what to do while you are caught up in the sliding snow: However, this advice is mostly obsoleted:

• Old advice: try to swim to the surface and roll to the side as you feel the avalanche coming to a stop.
  New advice: It is difficult to know which direction is up or to the side while you are caught up in a 100 mph avalanche.
• Old advice: loosen and throw away all equipment, which serve as markers for rescuers.
  New advice: Keep everything attached - it will be easier for people to find you if some of your equipment is sticking out of the snow. If you are rescued from an avalanche, you need all your equipment to get out of the backcountry, so hang on to everything.
• Old advice: Try to make a space in front of your mouth with your hands
  New advice: It is difficult to do this. Unfortunately, your breath will freeze the surrounding snow and create an ice mask, which inhibits air from circulating.

A lot of the old advice was derived from people who recounted their experience surviving an avalanche, and this data is obviously skewed - it would be ideal to also include information from people who did not survive.

The moment of an avalanche is the event horizon. Before an avalanche happens, you are in total control: you decide where to go and your risk exposure. After the avalanche, the avalanche is in control, and you have zero control over what is happening. It is better to spend time, energy, and money that will help you evaluate avalanche risk, rather than focusing on what to do after you are in an avalanche.

When an avalanche occurs, kinetic energy is released, causing friction between snow crystals, which melts the outer part of snow crystals. After the avalanche comes to a stop, the mixture refreezes. The resulting mixture is 3-4 times as dense as when it started out, and feels like concrete, which makes it very difficult to dig yourself out. The refreezing process also causes the snow to expand by about 3%. The expansion makes it feel like you are in a body cast, and reduces the space that your lungs have to expand. Because of this entombing process, it doesn't make sense to try to do anything like swim to the surface or get rid of things when you are caught up in an avalanche. The density of an avalanche while it is traveling down the mountain is 1-5%, which means you are likely to sink to the bottom.

Of the people killed in avalanches, 2/3 die from suffocation, and 1/3 die from trauma.

Route selection: what you fall back on if you encounter shades of gray.

Statistics from the Colorado Avalanche Information Center

Fatalities per country, 1986-2004

The difference in fatalities in different countries is mainly attributed to different attitudes about risks of backcountry skiing:

At Alpine Meadows, there are about 300 avalanche points where avalanche risk is determined. In 1982, 7 people were killed at Alpine Meadows in an avalanche that occurred within ski boundaries. Alpine Meadows was found not liable, because they demonstrated that they followed procedure and had taken adequate precautions.

In the United states, avalanche control is done for all areas within the ski area boundary. It is still possible to get caught in an avalanche in-bounds at a US ski resort, however the in-bound fatality rate since 1982 is zero. Class A ski resorts have one full time avalanche forecaster.

In Europe, there is no such thing as out of bounds: there is only on-piste and off-piste. No avalanche control is done on areas off-piste - that includes in the trees between runs. Prince Charles and a friend went off-piste to escape the paparazzi at a ski resort, triggered and avalanche, and his friend was killed. In Europe, the ski patrol charges a heafty sum for a rescue.

Trends

Over the past few years, there has been an increasing trend of more avalanche accidents, due to an increase in the skill level of the sport, without an increase in avalanche awareness. Also, backcountry snowpack is one of the most difficult environments to understand, even more difficult to analyze than whitewater rivers.

Age group correlation, 1951-2003

The 20 to 29 age group has the highest avalanche fatality rates:

Seasonal correlation, 1951 - 2003

A small number of avalanche accidents happen in summer: When mountaineering in the summer, avalanche awareness is still required when hiking snowy areas.

Fatalities by US state, 1986-2004

Colorado has by far the highest avalanche accident rate, due to two factors:

• Colorado has more unstable layers of snowpack: colder temperatures, along with a snowpack that is not as deep, generate faceted crystals that are more unstable.
• Colorado is a destination area that attracts visitors from all over the world intent on adventure.

Local Trend Correlation

The number of fatalities in the California/Nevada area has reduced in the past few years.

Sport type correlation, 1986-2004

Climbers and skiers in the backcountry have the largest number of avalanche fatalities. Snowboarders have a correspondingly small number of fatalities. The awareness among snowboarders has gone up significantly in the past few years. Snowmobilers have a high rate of avalanche accidents, due to a widespread lack of avalanche awareness. In particular, one snowmobile game is "high-mark," in which a group of snowmobilers see who can get the highest on a steep slope. The one who wins usually triggers an avalanche.

Training correlation, 1981-1997

The highest rates of avalanche accidents happen to people who have the greatest avalanche training (not necessarily experience), and also to people who have the highest skill in a snow sport:

	Skill level
Training	novice	intermediate	advanced
advanced	0%	0%	38%
some	0%	7%	28%
none	7%	8%	12%

Avalanche forecasting should be considered a skill sport: In addition to training, it takes practice to become proficient.

Time to rescue vs death, 1951-2003

The faster a victim is dug out of an avalanche, the greater the chance of survival:

Depth vs death

The deeper the victim, the greater likelihood of death:

Method of rescue vs death, 1951-2003

When digging for a victim, try to be quiet - you might be able to hear the victim. Sound travels very well into the snow (the victim can hear the rescuer), but sound travels very poorly out of the snow (the rescuers cannot always hear the victim).

An avalanche cord may not be effective because:

• The avalanche cord can form a rat's nest in the snow, making recovery take longer
• The avalanche cord may be embedded in concrete-like snowpack, and difficult to track.

Dogs are not effective because it takes a long time to carry them in: They cannot usually hike in, and usually must be brought in by helicopter.

Type of rescue vs survival, 1951-2003

The highest proportion of survivors are found by the victim's own party. It takes too long to bring in a rescue team.

Equipment

In the backcountry, there are three items that are required for avalanche rescue:

1. Beacon
2. Probe
3. Shovel

The probe and shovel can be used for measurement. In addition, it is useful to have a clinometer and a thermometer.

Beacons

There are two types of beacons: Analog and digital. Both work with each other. There are also a few beacons that can operate in both modes.

• Analog beacon: The beeps generated by the analog beacon get louder the closer you get to the victim. You must use the grid method to locate the victim. The analog beacon is good at locating more than one victim: you will hear different sets of beeps, and you can isolate one set and focus on it. Make sure an analog beacon has an external speaker (not earphones), a volume control, and a signal strength indicator light. If a strength signal is indicated by a number of lights, it's better to have more than 3 lights. The range of analog beacons is 75 to 100 feet, and requires an initial zig-zag search. The beacon is accurate to within a radius of 1/3 of the burial depth. A shorter range can actually work better, since the victim can be found sooner if you start close to the victim to begin with.
• Digital beacon: The digital beacon has two antenna, and will guide you along a dipole line of flux (usually in a curved path, not a direct path) to the victim. You have to move and turn slowly, to allow the beacon to determine the flux direction. The digital beacon is easier to learn how to use. The Tracker DTS is a popular digital beacon. However, digital beacons are not good at trying to locate more than one victim. An exception is the Pieps DSP Digital Avalanche Beacon, which has a computer that allows it to isolate multiple victims and lock onto the closest one ($350).

For people who don't practice often, a digital beacon is probably the better option, since it's easier to use. However, an analog beacon works as well as a digital beacon if you practice. All modern beacons were standardized to use the 457 KHz frequency in 1996. Prior to 1996, a different frequency was used that was less effective. Verify that everyone in your party is using a beacon that uses the 457 KHz frequency. Beacons have only a rescue function: they have no measurement or other use. If a beacon has an LCD readout, make sure it is visible in glaring sunlight.

Probes

Probes have cm marks, and can be used to measure snowpack depth. Get a probe that is at least 8 feet long. The resistance you feel as the probe penetrates layers can also give a rough indication of the snowpack layering. Probes are constructed like tent poles, and can be extended easily. They range from light to heavy (depending on price). Avoid probes with compression buttons - they get jammed with ice.

You can buy ski poles that can be taken apart and re-connected as probe poles, however:

• It is not convenient to use as a forecasting device
• In a rescue situation, it takes too much time to put together the equipment
• Parts of the ski poles can be lost in the process.

However, it does not hurt to have dedicated probe poles andconvertible ski poles as a contingency. Keep your probe in your backpack and within easy reach - you are more likely to use the probe for routine measurements if it's easy to get. Don't store a folded-up probe in a shovel handle.

Shovels

Get a shovel with a flat profile, to make it easy to do sheer tests. the larger the blade, the faster you can dig someone out. Avoid plastic shovels - avalanche debris is too hard for plastic shovels, and plastic shovels are not good for shear testing.

If you are going to lend rescue gear to other people in your group, give them the good stuff, because they may use it to rescue you. It is also a good idea to become an expert in teaching your friends how to use the equipment.

Ava-Lung & Airbags

Black Diamond developed the Ava-Lung, a vest worn over all other clothes. It gathers air directly from the snow through mesh panels which then is available to breathe through a snorkel. It also exhales the air in a different place that where it gets the air to prevent an ice mask from forming. The Ava-Lung will theoretically keep an avalanche victim alive longer before he suffocates. However, in the event of an avalanche, there may be a problem getting the snorkel into your mouth and keeping it there. There has been at least one incident where a guide was able to make effective use of the Ava-Lung.

An ABS pack consists of 2 balloons that expand. They provide flotation to keep you on top of an avalanche. About 60-70 people in Europe have been able to make effective use of ABS airbags in avalanches.

The Ava-Lung and the ABS packs should not be relied upon for safety. Instead, it is better to avoid avalanches in the first place. However, these devices can be effectively used when you are placing control of a situation in the hands of a guide. Even experienced guides can mess up big time. On January 20, 2003, seven people, including Craig Kelly, died in an avalanche on a guided tour as part of the Selkirk Mountain Experience (SME) in Canada. The skiers were guided by Ruedi Beglinger, considered to be a master guide.

Subjective justification

If you are about to enter an area and you are thinking to yourself: "now is a good time to set my beacon on transmit" or "now is a good time to get the ava-lung snorkel ready," re-evaluate the risk. If you have a gut feeling that a situation does not feel right, see if you can quantify the situation with actual measurements. Making observations to back up your gut feeling is sometimes necessary to avoid peer pressure if you are in a group that has a higher tolerance for risk than you.

Snowpack

A strong, heavy layer over a weak, light layer of snow represents a high avalanche risk. In the Sierra, storms often start with heavy, dense snow and finish with light, airy snow, called a right-side-up snowpack. However, if two storms happen back to back, the interface between the light layer from the first storm and the heavy layer from the second can be weak. Sometimes double storms happen so close together that you can't discern one storm from the next: these situations result in extremely high probability of avalanche. Back-to-back storms in the 1999-2000 season in Tahoe caused avalanches in Crystal Bay at Lake level.

Snow metamorphism

Snow starts changing the moment it lands. Snowpack can change from weak to strong and back over time. The warmer the temperature, the faster the changes. Elements of snowpack can include the following characteristics:

• Weak Layers
• Weak Interfaces
• Cohesive slabs
• Strong bonding between layers

One question to ask is how deep is the snow:

• Shallow snow sluffs in a loose avalanche
• Deep slab or climax release
• In between

Snow is more like air/atmosphere than like the ground: Skis and snowboards are actually "wings" that fly through the air.

Evaluating new snow:

• Faceted crystals: These are unrimed crystals. They are clear and will not stick to each other: you can't make a snowball with it. This type of snow creates an unstable layer.
• Rounded crystals: These are rimed crystals. They are"fuzzy" and will stick to each other easily: you can make a snowball easily. This type of snow creates a stable layer.

There are three types of metamorphosis:

1. Rounded - gains strength
2. Faceted - weakens
3. Melt-freeze - both

Rounding - dull / lackluster. Rounded crystals are created when the air is warm and the snowpack is deep. These conditions mean that the air in the snowpack is stagnant.

• No sharp points
• May have some straight sides
• Connective necks between grains
• Makes good snowballs

Faceting - Sparkles / looks sugary. Faceted crystals are created when the air is cold and snowpack is shallow. These conditions mean that the air in the snowpack is rising.

• Loose grains (no snowballs)
• Sharp points / striations - If a snow crystal has just one sharp point, it is always faceted.
• Straight sides / rounded
• Large pore spaces

Melt/freeze - Melt-freeze crystals are created when the air goes above and below 0° C.

• Glazed/slurpy
• Crunchy/gooey

Snow strength determination

Snow strength is determined by three factors:

1. Air temperature: Lay a thermometer on the surface in the shade.
2. Snow depth - use a probe to measure
3. Temperature at the snow-ground interface - this temperature will be 0° C outside of the arctic circle.

In a layer of snow, if the temperature gradient decreases by 1° C or more every 10 cm starting from the ground, faceting results, otherwise rounding results. Example: If the depth of the snowpack is 200 cm, the temperature of the snow at the snow surface must be colder than -20° C for faceting to take place. This analysis is somewhat simplified because it only works on a layer-by-layer basis. Some layers have gradients, and some don't.

The Sierra often has deep snowpack and warm temperatures, which creates rounded crystals. Most winds in the Sierras come out of the Southwest, pulling up warm air from the tropics (starting out with heavy, dense snow), then bring in lows from the North (ending in light, low density snow). In Colorado, the snowpack is typically shallow and cold, which tends to create faceted crystals. Therefore, Colorado is more susceptible to weaker faceted layers, and avalanche danger is typically higher. However, early in the season in the Sierra, you can have shallow snowpack and cold temperatures.

The dew point is the temperature at which the water vapor in air starts to condense. As water vapor rises, it reaches the dew point.

Radiation balance

If the solar radiation is S, and the terrestrial radiation is T, then rounding/faceting is determined as follows:

• If S == T, rounding occurs (air is stagnant). Often occurs in the middle of the snowpack. Typical for a cloudy day, with temperatures near 0° C. Typical for mid-season snowpack.
• If S < T, faceted gains form. These slopes are usually in the shade. In the Sierras, steep North facing slopes are often faceted because it stays colder, and is on the leeward side of the ridge, away from Southwesterly winds. North facing slopes also have the best skiing. Faceted snow often forms in the beginning of the season. Faceted snow often forms at the bottom of the snowpack: Ice lenses form near the surface. Faceted snow often forms near rocks and trees.
• If S > T, melt or freeze takes place. Often occurs on the surface of snowpack, or in spring snowpack. Often occurs on South facing slopes, caused by rain and freezing water.

If it snows early, the snow can create a faceted base, which means that every subsequent snowpack will slide easily.

Avalanche terrain risk scale

Factors include: Forces, Obstacles, Rescue Time (FORT)

The scale represents the avalanche potential, not the expected number of avalanches. Risk is also classified as low, moderate, considerable, high, and extreme.

References

1. Snow Sense by Jill Fredston & Doug Fesler, 1999. ISBN 0-9643994-0-7. This small book is condensed and to the point. It also focuses on decision making, and you can take the book out into the field with you and refer to it. It was one of the first books to provide avalanche prediction guidelines, based partly on information gleaned from interviews with avalanche survivors.
2. Avalanche Safety for Skiers, Climbers and Snowboarders 2nd Edition by Tony Daffern, 1999. ISBN 0921102720. A good reference. Published by Mountaineers Books
3. Sledding in Avalanche Terrain: Reducing the Risk, by Bruce Jamieson, 1999. ISBN 0969975872. A good guide for snowmobilers.
4. The Avalanche Handbook by David McClung & Peter Schaeter, 1993, ISBN 0898863643. Highly technical, engineering-oriented handbook, only useful for professionals. It's not for recreational backcountry skiers.
5. Snowy Torrents: Avalanche Accidents in the United States 1984, ISBN 0933160135
6. Snowy Torrents: Avalanche Accidents in the United States 1980-1986 by Nick Logan & Dale Atkins, 1996, ISBN 1884216528. A series of short case studies of avalanche accidents. From reading this book, it becomes obvious that people make the exact same mistakes over and over again.