How to Recognize Avalanche TerrainPublished on 04/03/2022 · 12 min readBefore venturing out into the sidecountry or backcountry this season, check out this guide by Ski Expert Hunter R. on recognizing avalanche terrain!
Photo by Hendrik Morkel
For skiers and snowboarders, particularly those who venture into the backcountry, there is one danger that stands out above all others. That danger is avalanches. Nearly every year fatal avalanches shake the ski community, and with climate change causing snowpacks to become more unstable every year, this is a problem that unfortunately will continue to get worse.
Any backcountry or sidecountry (“sidecountry” refers to the out-of-bounds areas at ski resorts) travelers should carry backcountry safety gear and be confident in how to use it. However, the best way to avoid danger in the backcountry is to mitigate the risk of being caught in an avalanche in the first place. The best way to do this is to be aware of what qualifies as avalanche terrain and avoid spending much time in these places, particularly when dangerous conditions are present.
Though this article is a great place to start in understanding your surroundings while out in the backcountry, it is in no way meant to be a replacement for formal avalanche education through a certified guide service. These courses save lives and give you great practice in using your knowledge and skills!
Avalanche probability is a result of three factors working together: weather, snowpack, and terrain. Paying attention to snowpack and weather is important. Information on these two factors can usually be found on the front page of your local avalanche-forecast website. (Here’s an example from the Utah Avalanche Center if you’re not familiar with these). During the winter, these websites normally publish a daily update of general snowpack conditions, current avalanche issues, danger for the day, things to pay attention to, recent avalanches, weather, etc.
With snowpack and weather out of your control, the one thing you have some control over when it comes to avoiding being caught in an avalanche is the third factor: terrain. Though avalanches can happen almost anywhere with a significant amount of snow, there are a few types of terrain that are much more prone to slides and much more dangerous in the instance that they do slide. In this article, we will talk about the main things to watch out for when choosing terrain in which to backcountry tour.
First, let's talk about what causes an avalanche. In short, all the layers of snow accumulation throughout the season stack on top of one another. In a perfect world, these layers would all bond together well, but different factors, such as temperature or weather fluctuations, will cause some of the layers to bond poorly to the other layers, creating instability.
An avalanche occurs when the stress from gravity or from an applied weight, such as a heavy new layer of snow or a skier, is greater than the strength of the bonds between the snow layers.
The two most common types of avalanches are loose-snow and slab avalanches. While I’ll elaborate on these later in the article, here is a short definition for each:
- Loose-snow avalanche: When a bit of loose snow or ‘sluff’ on the top of the snow slides down. These are usually not large, not as dangerous, and occur below you as you are walking up or skiing down.
- Slab avalanche: These are the most dangerous and account for almost all avalanche deaths. A “slab” is a plate of snow, and in these avalanches, the whole plate slides on the snow underneath. They are much more dramatic looking and will appear as a fracture in the snow. They are easier to trigger and usually break above the skier/snowboarder causing them to be caught in the avalanche. For reference of how fast and dangerous these can be, the bonds holding the slab in place fracture at about 220 miles per hour (mph). The avalanche reaches 20 mph within the first 3 seconds, and 80 mph after 6 seconds. They vary in size but on average, these avalanches are about 180 feet across and 1-3 feet deep. That's a lot of snow!
Okay, now that we've got some terminology down, let's get into terrain!
A common phrase in the backcountry world when trying to decide where to tour is “keep it below 30”, with 30 referring to the slope angle of the area you are planning on touring. The reason behind this phrase is that, as shown in the graph above, 95% of avalanches happen in terrain that has a slope angle between 30 and 45 degrees. It doesn’t mean that slopes outside of these angles are immune to slides, but it does mean that if you are traveling on slopes between these angles, you are certainly in avalanche terrain and should proceed with caution.
The slope angle of an area can usually be seen on mapping software, such as CalTopo (seen above), and can be measured while you are in the area with a slope inclinometer, such as the BCA Slope Meter or the Poleclinimeter. Slope inclinometers are very inexpensive (usually less than $25), are small enough to fit in your pocket, and are worth carrying just to be on the safe side.
Essentially these can be used by holding them up to a slope to measure the angle. If it's between 30 and 45 degrees, you can know to either avoid it and find something less steep or proceed with extreme caution.
Aspect to the Wind
Aside from the angle of the slope you are planning on skiing/snowboarding, you should also take note of the slope aspect in regards to both the wind and the sun. Some terrain can be more prone to avalanches due to its closeness to an area that gets a lot of wind. The wind will carry snow from one slope (called the windward slope) and deposit it on a different steep slope (called the leeward slope). The leeward slope gets an unstable buildup of snow, which increases the likelihood of the area to slide.
This can happen in two different ways: top loading and cross loading. Top loading occurs on the top of a ridge when the wind picks up snow from one side of the ridge and deposits it on the other side of the ridge. Cross loading occurs when it's particularly windy on one side (windward side) of gullies or chutes, and the snow is carried to the other side of the gullies or chutes (leeward side), making that side have a build-up of unstable snow.
You can tell that an area might be wind-loaded because it will look smooth and round despite no recent heavy snowfall. Sometimes on a windy day, you can see this occurring in real-time. It will look like snow is flying up from a ridge or gully (as can be seen in the photo below).
Aspect to the Sun
The aspect of a slope to the sun is also important. Shady aspects or aspects facing north and east, which tend to get less sun, are generally more unstable than aspects that get more sun, such as those facing south and west. Because of the colder temperatures on the north- and east-facing terrain, the snow here tends to develop into ice crystals—kind of like morning dew on your lawn.
When new snow comes and lays on top of the ice-crystal-shaped layer of snow, the new snow is balancing precariously on top of a layer of ice crystals. This makes for a weak layer in the snowpack and makes triggering slab avalanches easy to do!
Warning signs to look for when testing for this ice-crystal issue include looking for a grainy, almost sand-textured snow layer and recent avalanche activity on aspects facing the same direction.
The last thing to note about slopes is the shape of the slope. Though this has less of an effect on avalanche probability than the factors mentioned above, it still has some effect in that convex slopes are more likely to slide than concave or planar slopes.
This is due to a few factors, most notably there is less support for the snow at the bottom of a convex slope and it is more easily wind loaded. Due to its rapid downturn, it's also a bit harder to travel safely on these slopes, the snowpack conditions vary greatly from the top of the slope to the bottom, and they are a sort of terrain trap, which we will talk about next.
Outside of slope angles and aspects, another thing to be wary of when traveling in the backcountry is terrain traps. Terrain traps refer to terrain where the consequences of an avalanche will be much higher than if the avalanche were to occur elsewhere.
The two most common issues in terrain traps are that they put you at risk for either a deep or being carried into dangerous terrain if you are in an avalanche.
Gullies, crevasses, and lakes are the first type of terrain traps. They are particularly dangerous because if an avalanche were to occur in these areas, the debris would all be piled in one place, called the “runout zone”. If you happened to be in the runout zone when an avalanche occurred, you would have a much deeper burial due to all the avalanche debris. This would require more digging from your rescuers which would take more time and therefore minimize your chances of survival.
Cliffs, benches (a strip of flatter ground with a steep slope above and below it), and rock fields are examples of other kinds of terrain traps. Maybe you are skilled enough to ski these areas well, but if an avalanche were to come and take you out, you would be pushed off a cliff or jostled around in a rock field, both of which would increase your likelihood for injury or death.
Here are a few examples of terrain traps to avoid in the backcountry because they increase the danger you would be in if there was a nearby slide:
Past Avalanche Activity
Maybe obvious, but a great thing to look for to assess if you are in avalanche terrain is signs of past avalanche activity. If there has been an avalanche in an area recently, you can normally tell because the avalanche track will still be visible in the snow or avalanche debris will be visible in the form of piles of chunky snow (image shown below).
Other clues when looking for evidence of past avalanche activity is to look for areas of downed trees, an area of no trees in an area that otherwise has a lot of trees, or an area of fairly young trees among otherwise large trees. Since the force of an avalanche usually wipes away the vegetation in an area, studying the vegetation when trying to figure out if an area is prone to avalanches is normally a pretty good sign!
Some areas that slide don’t have as much vegetation, so it's also worth reviewing your local avalanche forecast website to search the area you are planning on touring just to make sure you have all the info on areas that have frequent slides. As an example, the Utah Avalanche Center (UAC) has a map feature that shows where avalanches have been reported in a specified time frame and marks where there have been fatalities.
Travel Tips for Safety
Now that you have a general idea of what types of terrain constitute avalanches, here are a few tips for staying safe while traveling in the backcountry.
Again, reading this article is no replacement for taking an avalanche course with a certified guide, but it is a good start to understanding your surroundings before your first day out on the snow!
Do your research on the area you plan to ski and the weather of the day you are going. Don’t go alone or with people whose decision-making you don't fully trust. Make sure to have a good idea of the skill level of everyone in your group so that no one gets in over their head. Plan your route up and the path you plan to ski down, and stick to this plan as closely as you can. Choose your touring partners carefully as these will be the people in charge of saving your life if anything goes wrong. Make sure everyone agrees and feels good about the plan. Have an escape route planned out ahead of time in case anything happens and you need to think quickly—it’s good to know what’s around you.
Before heading out, always check the forecast, look for recent reported avalanche activity, and always tell someone at home where you are going, and when you are planning on being back. Do a beacon check, testing your partners’ avalanche beacons as well as your own, at the trailhead.
Always pack avalanche safety equipment, such as a beacon, shovel, and probe (and avalanche airbag, if applicable). Make sure you have a first-aid kit, extra layers, water, snacks, and a headlamp just in case. Each winter, be sure to practice with your avalanche-rescue equipment so if you need to use it, you will be able to do so with confidence and speed.
Only travel one at a time across avalanche terrain. Watch your partners. Don’t ski above your partners. Communicate effectively if anything changes.
Lastly, have fun! Backcountry skiing is dangerous, but also one of the most exciting activities and a beautiful way to experience the outdoors. Good planning and preparedness can help you avoid many catastrophes so be sure to take an avalanche course prior to heading out for your first time and make sure your gear is dialed in!
If you have any other questions regarding backcountry safety, ski gear, trip advice, etc., hit up a Ski Expert on Curated, and we would be more than happy to help you get outside safely this season!