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Preparing for Avalanche Terrain

by Colin Zacharias
Professional Mountain Guide and Mountain Safety Specialist

In 1976 I took my first avalanche course, taught by Alaskan avalanche guru Dave Hamre. I hoped (naively) that by the end of that weekend I would to be able to make that "go or no go" decision on which slopes were safe to ski. After 24 years in the avalanche business there are still days when I can't make that decision with absolute certainty or accuracy. It is a difficult task and an elusive goal, but I do have a process and a knowledge base from which to make decisions.

Photo: David Bishop

Terrain choices are the result and consequence of each backcountry winter traveller's "personal hazard forecast". The backcountry traveller must consider the weather forecast, snow stability and conditions, recent or past avalanche activity, and the people in the group and then choose a ski route or a slope appropriate for the given day. This article reviews a few of the processes taken by recreational skiers, riders, and sledders to arrive at the "go or no go" decision in the terrain.

Pre-Trip Plan: Know Before You Go.

Pre trip planning sessions help to mitigate hazards.

Maps and guidebooks often describe the terrain that will be encountered on a proposed trip. Ask friends and local guides what slopes have a history of avalanching. Go online to research avalanche and snow conditions. Relate the trip options to what is known about snow and weather conditions.

The most important task is to create options prior to departure.

Select three options for each trip in the category of IDEAL, SAFER, SAFEST. Your IDEAL trip would be chosen if all the stars align in terms of snow stability, weather conditions, ski conditions and group skill, compatibility and fitness. Simplify your terrain choices as the situation becomes more complicated. All three options would be within the parameters of the travel advisory or danger rating published at the time.

Making Terrain Choices

Danger Rating

Probability the backcountry travellers will trigger avalanches or be exposed to natural avalanches in or adjacent to avalanche terrain



Terrain Criteria


Low Danger


Best time for ski traverses, or higher elevation trips with steeper terrain. Caution shallow weak snowpack areas, and/or during atypical years like 2003.


Moderate to Considerable Danger


Plan several options as opposed to one. Be aware how conditions change over elevation, exposure to wind or sun. Increase caution or avoid slopes >35°; avoid slopes with terrain traps; caution after storms, wind events; or atypical snow years. Beware of rapid temperature changes; light rain. Check the bulletin for "persistent weak layers" in the snowpack and avoid those aspects.


High to Extreme Danger


Choose forested terrain; avoid open slopes or known avalanche paths and avalanche run-outs. Stay off lee slopes. Travel on low angle slopes or ridges. If the danger rises to extreme consider going to the beach.

As uncertainty increases so should your margin of safety

* The terms “complex, challenging and simple” are derived from Parks Canada’s new terrain descriptors and exposure scale. Parks uses terrain criteria that is different from the above descriptions and lists trips in each category. The terrain ratings are used together with the avalanche bulletins to assist parks backcountry users in deciding which trip is appropriate for the given conditions.

For more information read the Avalanche Terrain Ratings on the Provincial Emergency Program website.

Weather and snowpack conditions are best derived from the Public Avalanche Bulletins.

The Canadian Avalanche Centre (CAC) and partners including Parks Canada, Whistler Blackcomb and the North Shore Avalanche Advisory publish the avalanche bulletins. People underestimate the value of the bulletins. The bulletins summarize observations from more than 100 professionals that work in the BC and Alberta mountains each winter day. Each bulletin provides a description of how the weather is affecting the local snowpack and allows the weekend recreational backcountry user to keep track of weak layers, note avalanche occurrences, and gives a valuable travel advisory with each posting.

Know your partners prior to departing.

A good mix of abilities and personalities assists your terrain choices. Experience in the terrain is invaluable, but so is a fresh set of eyes in the terrain. Ensure your partners have experience with companion rescue skills.

En Route: Red Flags Lead The Way

When en-route, reassess, re-evaluate and if necessary re-route.

Avalanche activity is nature's danger sign.

Are there signs of activity? Is it isolated or widespread? At what elevation or aspect? How recent? Even in poor visibility one may see signs of recent avalanche debris at the bottom of slopes.

Photo: Bruce Kirkby

Bow Lake, Banff National Park

What can you observe about the weather and snowpack?

When was the last snowfall? Is there more snow that the morning bulletin or ski report suggested? Can you see blowing snow at ridgetop? Is the sun a factor? Beware of rapid change! How do conditions change as you travel through valleys or change elevation?

How is the group doing?

Are they fit enough for the proposed trip? Skilled enough? Is the group participating in the hazard management? Are they communicating well?

Now you are en route, exercise the best option.

Is the IDEAL route still the one of choice? Or should you branch off towards the SAFER route? Are conditions worse than you had hoped, and if so is the SAFEST route becoming the natural choice?

On The Slope: To Go or Not To Go?

As previously mentioned, terrain choices are the answer to one's snow stability and hazard evaluation. Therefore one must match the terrain choice to ones ability to evaluate hazard. If one lacks confidence evaluating the hazard from snow avalanches it doesn't make sense to exercise a confident terrain choice.

Try to answer your own terrain questions: Can the slope produce avalanches?

How steep is steep?

Slope Angle

Literature describes most avalanches occurring on 35-45° slopes. Yet the stats in Bruce Jamieson's book "Avalanche Accidents in Canada Volume 4: 1984 – 1996" illustrates most avalanche fatalities occur on slopes with start zones 31-35° (followed by 36-40°). Consider that the human trigger (skiers, riders, snowmobiles) could be a factor in initiating avalanches on these lower angled slopes. Get out there and start measuring and you will discover that most slopes that are fun to ski are pushing 35-38°!

Is wind a factor?

Wind is often underestimated as a factor in human triggered avalanches. Lee slopes (as opposed to windward slopes) are where the snow can load more rapidly than anticipated. Bruce Jamieson states that snow loading on lees slopes can be two to five times the rate of newly fallen snow. Up to ten times in certain conditions! During a few hours snow can accumulate from wind transport and create a dense slab over a weak layer. Snow begins to drift at 20kph; 35kph is ideal wind for moving snow from one side of the mountain onto the protected lee slope.

Is this change in temperature affecting the slope?

Again, beware of rapid change. In late February a few hours of intense sunshine on a winter snowpack can make a difference and result in avalanches. Also light rain for a few hours has been known to initiate avalanches on terrain with certain snowpack characteristics.

Is the snow unstable or not?

Terrain configuration and snowpack structure are inextricably linked. Hopefully you have jotted notes down from the morning avalanche bulletin and can compare your notes to what you observe in the field. A quick snow profile may illustrate the layering discussed in the bulletin or by comparing the layer of new snow you may discover you are in a deeper snowpack belt than the average location. Avalanche activity is the best illustrator of snow stability, but a test profile or rutschblock test may indicate layers of which you may have been unaware.

People and Exposure: what will happen if an avalanche does occur?

Standing near avalanche terrain it may help to engage this question. Are you exposed to slopes above? Could you trigger an avalanche from where you intend to travel? Will you or any member of your group be carried down if an avalanche does occur? Will it be a large or a small avalanche?

Ask yourself if you and your friends are prepared to respond with a "companion" rescue. Have you been practising lately with the avalanche rescue gear? Have you practised a deeper burial for which you have to probe?

Safe Travel

You have chosen one of your SAFER options. The skiing is great and you feel good about your decision. Even though the powder is fantastic, focus on how terrain use can minimize the likelihood of triggering avalanches. Most guides stay alive by careful terrain use and even when they ski the slopes with several guests at a time the terrain is chosen with safety parameters in mind. ALWAYS carry as a minimum the basic tools of avalanche rescue: transceiver, probe and shovel.

Photo: Jia Condon

If in doubt use "safe travel techniques"

In confined terrain (gulleys, steep chutes, narrow glades, ridges) ski one at a time. Ensure you post a safety who (from a safe viewpoint) can see the pitch the skiers are enjoying. On larger bowl like features where you may be skiing together on long slopes, have each skier or rider wait several seconds between each person leaving the top. This way each skier is more than three or four turns apart.

Communicate clearly to the group where you want them to ski.

Avalanches are often triggered from zones of weaker strength snow. Wind scoured, rocky and steep sections of the start zone are to be avoided. Avoid steep convex rolls, especially if they are wind affected. These features and terrain configurations should be communicated to each group member prior to skiing down the slope. In the trees have skiers or riders descend with partners. If a small slide into a terrain trap (creek, gulley) occurs, the partner is the best chance for a quick recovery.

Terrain decisions are unanimous.

The decision which terrain to choose is best made as part of a group process. Be aware of how human factors affect an individual's ability to make the best choice. Familiarity, apparent confidence, insecurity, fatigue, cold and other factors reduce team member's ability to make good choices. It could be as simple as the new guy noting the rapid change in temperature and the veteran who's done the trip five times not noticing. If there is one dissenting voice consider the terrain choice vetoed.

Take Time in the Terrain

To paraphrase Karl Klassen, editor of the ACMG, "Technical Handbook for Professional Mountain Guides" it is terrain that draws (people) to the mountains, and terrain, in one way or another, relates to practically every decision (a backcountry traveller) makes.

Terrain to some degree or another illustrates itself. We can measure slope angle and length, elevation and aspect. Conversely much of the processes within the snowpack remain invisible to our eyes. Our process begins with terrain. It starts with a wish list of where we would like to go, and finishes with the long slopes we wish to ski and the method by which we ski those slopes. Our choices and methods therefore demonstrate what we understand about the snow and the hazards of avalanches. Knox Williams of the Colorado Avalanche Information Centre suggests that attaining an avalanche education is a life long endeavour. "No matter how much you learn every winter will bring new revelations and challenges…you will be studying in the most wonderful classroom on this planet-the lofty domain of mountains".

I have been working in the avalanche industry since 1980. I started by working with the Parks Canada Avalanche Patrol Team at Marmot Basin. I went on to work for BC highways and as Avalanche forcaster for the alpine events at the 1988 Olympics.


This site provides some information regarding avalanche safety. It does NOT contain everything you need to know to protect yourself from avalanche risks.

The information on this site is "as is". It might not be current, complete, accurate or correct, so please do not rely on it. Mountain Equipment Co-op will NOT be liable to you or anyone else for any damages, injuries or death that might result from your reliance on this site or any information on it.

Always get advice from an avalanche expert if you are thinking about entering potential avalanche areas.