Snow Avalanche avoidance begins with careful route planning. Each planned route involves important safety considerations and exploratory tests. No route is without risks. The information below is basic and not comprehensive. It is intended as an outline of the main dangers and precautions that can be taken.
In addition to selecting routes with less risks, every trip plan needs to consider weather and avalanche forecasts. Weather conditions leading up to the planned event must be monitored and existing snowpack conditions need to be considered.

Ideal Routes
Ideal routes are typically those with lower slope angles and dense forest leading up to broad, open ridgelines. If the slope is below 30º there is insufficient slope for a snow slab to glide. A forest helps anchor the snow and hold it in place, reducing avalanche risks, and a broad ridgeline provides a path that is wide enough to avoid cornices. Finding low-slope angle routes is not always possible and that’s when plans need to adjust to find a route through anchor points such as trees.
Campsite sellection
Ideal routes also allow sufficient time to reach the intended camp area. The ability to reach camp depends on the conditioning of the group, the distance, and the snow conditions. Several days of 18-inch snowfall can create thigh-high snow and make traveling even three miles an all-day effort, whereas traveling on hard consolidated snow is relatively easy.
An ideal campsite will depend on the preferences of the group. For me, it is on top of an open ridge or wide summit. This is ideal because this is where the best views are to be found. It is also safer because you are less likely to be in the path of a potential rockfall or avalanche. Snow-loaded trees falling over is another hazard to avoid.
The main challenge of ridge-top campsites is the winter winds and Springtime lightning exposure. For high winds, you must build a snow wall and for lightning, you usually have to evacuate the ridge as quickly as possible. Lightning is somewhat rare and more easily avoided by rescheduling based on the weather forecast. Avalanche and rockfall are more persistent winter terrain hazards. The ability to get out of avalanche and rockfall terrain and reach a safer campsite needs to be calculated into the plan.

Understanding and Avoiding Avalanches
Slope Angle Importance

Low and high slope angles produce fewer avalanches and less danger. The closer the slope angle gets to 38–39º the more the danger increases. Avoiding slopes that are 32–45º is one way to reduce risks. In some areas, a slope in the 35º range may be anchored by trees making it more stable and safer than a 35º slope that isn’t anchored. The process of evaluating a slope begins by looking at the slope angles on a topographical map and then examining satellite images of the same terrain to look for potential route anchors.
Examples of Route Planning

Map 1A shows the established trail (red dotted line) going through a an area with 30–45º slope angles. Entering this area could trigger an avalanche that flows down into the area near the lake.

Map 1B: The satellite image of the same area shows insufficient forest to anchor the route, so the route has to change to avoid the steeper slopes. The white dotted line indicates the safer route.

Map 2A shows the established trail (red dotted line) going through an area with 30–45º slope angles.

Map 2B: This satellite image of the same area shows forests that could anchor the route. The satellite shows a more direct route but remember established trails exist for a reason. The alternative straight route (indicated by the white line) through the trees may involve some terrain obstacles not observable in the satellite image. This route should be tested first by experienced winter backpackers.

Map 3A shows the established trail (red dotted line] going through an area with 30–45º slope angles. Satellite images show insufficient forest to anchor the slopes. There are two possible lower-angle ways to access the top of the ridge — a short route and a longer route.

This image shows the short route. Once we were in the area we could a stack of cornices going up the ridge. While it is possible to traverse the slope next to these cornices, the longer route is the safer and easier option.

Map 3B: This map shows the longer route and a possible shortcut. We made successful trips to the ridge using the longer route. Then one year the lead navigator cut up the ridge into the steeper slopes. This shortcut put us on terrain in the hazardous range and before we could reach the top of the ridge a slab avalanche was triggered (shown below).


There were three snowshoers and the avalanche broke a few meters behind the last person in the group. For that reason, no one was caught on the slab. This incident shows the importance of staying on the low-angle slope and making sure that all team members understand the route plan, especially the lead navigator. The area in the higher slope angle was small, yet the slab still broke. There was no indication, such as visible crowns, in the area to indicate the probability of a slab avalanche.
Spread Out to Cross Avalanche Terrain
As a general safety rule the group should stay close together — close enough that communication. However, when crossing avalanche terrain (30–45º slopes) the group should spread out and allow each person to cross one at a time.

Measuring Destructive Force
The destructive force of avalanches is measured according to a “D Scale” with levels D1 (not dangerous) to D5 (destroy a village). The slab avalanche shown above is in the D1–D2 range, slightly less than a meter thick at the crown — but potentially able to bury a person.
The avalanche occurred with a loud bang, quickly propagated down the ridge, and slid down the slope in a matter of seconds.
Priortize Safety
Use avalanche gear. Even with careful planning, always be equipped with avalanche gear. Practice beacon recovery, probing, and shoveling skills. Avalanche gear can be expensive but if you plan on doing any backcountry winter recreation the cost is justified. It can save your life or the life of someone else. Get the gear and start the learning process.
Types of Avalanches
Loose Snow Avalanches
Description: Avalanches that originate at a single point and collect more snow as they descend. They involve loose or unconsolidated snow and are common on steep slopes after heavy snowfalls. These are common in the Pacific Northwest and can usually be seen on slopes. This type of avalanche activity is sometimes called sluffing.
Characteristics: Usually small and less dangerous than slab avalanches, but dangerous in confined terrain.
Slab Avalanches
Description: A slab avalanche is a type of avalanche characterized by the release of a large, cohesive block of snow from a weak layer within the snowpack. These avalanches are considered very dangerous due to their size and tendency to sweep over and engulf people. Slab avalanches have a long fracture line that quickly propagates along a ridge. Slabs can occur when a bonded layer of snow (the slab) is lying on top of a weak layer over a sufficiently large area. Slab avalanches are triggered when an additional load is applied to the slope and the slope angle is 25° to 50º. Most occur around 39º. Slab avalanches can be triggered by skiers, snowshoers, snowmobiles, and cornices collapsing from the heat of the sun or wind.
Characteristics: Slab avalanches are often triggered by natural factors like snowfall or temperature changes, but can also be triggered by human activities. They can release a canon-like sound blast and travel at high speeds. They are considered the most dangerous type.
Wet Avalanches
Description: These occur when the snowpack contains significant amounts of liquid water, which can weaken the snow and make it slide more easily
Characteristics: Wet avalanches are often shallow, usually travel more slowly than dry avalanches, and have a predictable runout.
Glide Avalanches
Description: These involve the entire snowpack or a large portion of it sliding down the slope on a lubricated layer, such as wet meadow vegetation or slick or loose rock, often due to water or melting snow. In the Pacific Northwest, this type of avalanche is usually small and rare.
Characteristics: They can travel considerable distances and are less common than loose snow or slab avalanches.
Powder avalanches
Dry avalanche that can involve a large cloud of powdered snow. These are rare in the Pacific Northwest.
For more about navigating avalanche terrain, I recommend Avalanche Essentials: A Step-By-Step System for Safety and Survival by Bruce Tremper.
Other Types of Hazards
Snow Bridges
Concealed subnivean streams are created when snow builds up on the banks of the stream and then lean in concealing the stream. This buildup of snow can be many meters deep and create a weak snowbridge or hidden snow well.

In this photo, a hiker tests the depth of a hole with an avalanche probe. He fell through the snow creating this hole. Two hikers passed over the same spot without knowing the snowbridge hazard existed. The hiker that fell through was unable to touch the bottom and struggled to get out. The hole is a gap above a stream. This means the hazard extends throughout the area above wherever the stream flows.

Another example of a concealed stream. The existence of the stream is only known by reference to a map or the appearance of an opening such as this one.

This photo shows the normal trail route over a shallow stream and then up a bank of snow or snowbridge. Once down the snow bank, the group could see that stream water was running under the entire snow slope meaning the area could break free and fall into the deep rocky ravine and cold water on the right. We decided to go off-trail and find a safer crossing on our return.
Precautions:
- Trail maps often show where trails cross streams and creeks. Be aware of these crossings because they may be hidden in the winter.
- Study the terrain carefully as you hike watching for signs of streams such as meandering depressions in the snowscape, waterfalls, and the sound of running water.
Snow bridges on snowfields


The above two photos show the dangers of crossing snowfields. At the end of winter, many snowfields are solid and easily support hikers. Gradually these snowfields melt out. The critically important thing to understand is that snowfields don’t just melt from the top down. Snowfields and glaciers melt out from the bottom. This process of melting is accelerated by water flowing down the slope under the ice. This creates a hidden ice cave that eventually collapses. Hikers can fall through the ice 10–20 feet or more onto the rocks below and sometimes into freezing water. If the snowfield has a natural creek, such as Aasgard Pass, this process will occur earlier in the season, with hazard spots appearing in early June. Snowfields such as Spider Gap will become more hazardous in July. In the case of Aasgard, a safer route up is on the left (Northeast) side of the snowfield. In the case of Spider Gap, the safer route is over the ridge on the East side of the pass.
Tree wells

Tree wells typically form around large trees. Some tree wells can be 10–20 feet deep. The well itself can contain snow, but the snow is less consolidated. If a skier or snowshoer falls into the well, there is a risk of Snow Immersion Suffocation (SIS). Getting out of a tree well is difficult because the soft snow offers no support. Even with rescue assistance, getting out is difficult and time-consuming with a risk of hypothermia.
Wells and air pockets can also form around rocks and fallen trees. They can be formed by falling snow, streams, and wind. Tree wells that form around fallen trees are usually small. They can form even in open spaces where there is no visible sign of a tree or around hidden rocks or bushes on the tops of windswept ridges. Sometimes a small tree above the snow is the tip of a large tree. The wells are one of the main reasons why you should never snowshoe or hike alone on snow.
Precautions
- Never travel on snow alone.
- Avoid getting too close to trees.
- Watch for small holes or depressions that may indicate a larger well or space below the snow surface.
- If possible, place trekking poles into an X shape with your hand at the center point of the X to gain support in the snow.
Forest Rain and Icicles
There are several types of forest hazards that are commonly overlooked.
Moisture: On clear days, the sun warms the trees, and snow melting in the trees creates a rain shower throughout the forest. This creates a hypothermia risk if backpackers assume that there is no need for rain gear or a pack cover or securing their own gear from moisture.
Falling ice and snow: Another hazard is falling icicles. Some icicles can be as large as logs. I was once hiking along side a rock face when a meter long icicle hit the trail a few feet in front of me. The diameter was the size of the football.
Usually, icicles are small but falling from high above they can still cause injuries. For this reason, it is helpful to wear a climbing helmet when snowshoeing through a forest.
Rockfall Hazards
Rockfall is also a common hazard particularly when crossing gullies on steep slopes where there is a lot of erosion. The experience of winter backpacking makes one aware that rockfall is extremely common. In the spring, the snow is often covered with scattered rock debris, large and small, falling from slopes and cliffs. It is apparent that the rockfall is recent because the rocks are on top of the snow. If you are near a rocky slope and temperatures are rising and falling around the freezing level, the moisture freezes and expands causing the rocks to break. You can hear rocks falling throughout the night.
Precautions:
- Don’t camp below rocky slopes. Be careful where you camp and hike and always wear a climbing helmet.
- Don’t linger below rocky slopes. Move quickly to safer terrain.

Open Stream Crossings
Another hazard is overflowing streams. In the early spring when the snow begins to melt, many visible stream crossings have elevated and raging water. If the stream is large enough to be named on a map, you may have to follow the bank of the stream for some distance to find a way to cross it. Falling in cold water is a serious hypothermia risk. If this happens, you need to stop the hike and focus on hypothermia prevention.
Precautions
It is not uncommon for hikers to drown in streams. It is easy to underestimate the force of even shallow running water and how slippery rocks can be. Take these important precautions:
- Unclip your hip belt and sternum strap in case you need to free yourself from your backpack.
- Face upstream. In a group, face upstream with each hiker behind the lead hiker. Everyone faces upstream, moving forward and sideways at the same time as they cross the stream. You can also use a tripod formation with arms together and the strongest person in the upstream direction.
- Keep 3 points of contact at all times. Use trekking poles or a branch
- Scout around to find the safest point to cross. A lengthy delay or detour is better than trying to recover from a fall while crossing.
- Be mindful of stream traps downstream
- Look for unstable rocky or snowy shores.
- Look for narrower areas to cross upstream or slower water flows in areas where the stream braids out.
- Be mindful of trees coming downstream or stuck in the path downstream.
- Carry a change of clothes or dedicated camp base layer. Hikers don’t usually carry a change of clothes on short winter trips, but every hiker should always be equipped with a fresh base layer that they can change into, along with a hardshell (rain pants and jacket). If the stream crossing is known and hazardous, pack extra clothing.
- Use river shoes: If you must get in the water, plan ahead and bring river-crossing shoes (purpose-designed for water). As much as possible, try to keep your boots and clothing dry, but don’t cross barefoot because that will increase the chances of slipping.
- Do not attach a rope to a person crossing a stream. Ropes can cause a person to get pinned under the water, entangled, and even strangled. They can grab onto a length of rope but the rope should not be attached to them. That said, rope is not common gear for winter backpacking.
- Cross in the morning: If possible, cross in the morning when snow melt is reduced and the stream is lowest. Snow bridges tend to be stronger in the morning.
- Avoid log crossings because longs can be slippery and unstable. If you must use a log, use microspikes and be sure the log is stable.

Cornices
When hiking or camping on a ridge there is the possibility of a cornice being nearby. These are often imperceptible from the top of the ridge. The area below the cornice may be a short distance (gradual runout) or a large distance with a potentially fatal runout. Most cornices are recurring and often predictable on a map.

Safety precautions
- Don’t walk over to the edge of a snowy ridge to look down.
- Stay as far away as possible from the edges of steep slopes. The narrower the ridge, the more important it is to move down the windward side of the slope. Cornices in the Pacific Northwest can easily extend out 6–7 feet (overhang). I have photographed ones that were larger.

Runouts
Dangerous runouts are a common characteristic of mountain travel. These are sections of a route where it is hazardous if you slip or fall. The consequences can be injury or death. A level trail above a steep drop-off may be relatively safe in the summer but once covered in snow, the path is no longer level. Typically, this problem is greatest in the springtime when the snow is melting out and hard snow remains across the trail in steep ravines and couloirs.


On an unsafe runout, a hiker who slips will then slide and potentially go off a cliff or collide with rocks and trees at a high speed. A safer runout has two features:
- A long slope that ends in a flat area where there are no trees or rocks to impact.
- A long slope that allows sufficient time to self-arrest with trekking poles or an ice axe.

Safety precautions
- Look for a route with less dangerous runouts.
- If the snow isn’t too hard, remove snowshoes and post holes across the route for greater stability.
- If the snow is hard, use microspikes or crampons.
- Turn back. If the risk level is beyond the experience and comfort level of the group, turn back. Sometimes the route can be covered with hard windblown ice and even crampons can’t provide sufficient traction. It is important to recognize the danger and turn back.
- Be aware that it is easy to go up a steep slope in snowshoes but much harder to come back down. Snowshoes have crampons and side wall traction better suited for going up than coming down. Take care to not put yourself on a slope you cannot descend safely.
Climbing Helmets
Most backpackers and hikers are not used to the idea of wearing climbing helmets. Accidents involving falling are more common on snow and ice. You can slip on a slope and quickly collide with a rock or tree. Ice can fall from trees. Rocks can fall down ravines and cross the trail colliding with your head. For these reasons, whenever you head out on terrain that requires snowshoes or crampons, wear a climbing helmet. Also, a climbing helmet is the most secure way to wear a headlamp when hiking in low light. Remember, helmets work best when they are on your head rather than attached to your backpack.
Route information (distribution to attendees)
Always distribute the complete event and route plan to all attendees. This should include:
- Trail names and numbers
- Links for trail on trail Apps
- Map driving directions to the trailhead.
Caravan from the meetup location. Once you arrive at the trailhead there is often no cell reception for contacting drivers who don’t show up.
Contact Information
It can help to exchange phone numbers and/or InReach numbers. Often phone satellite messages are quicker than InReach messages because the phones use lower elevation satellites.
Let us know your thoughts and suggestions
Please share your ideas, experiences, and challenges below. Your comments and questions are welcomed.
