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Knowledge is your best defense against the danger of avalanches, and there’s no better way to gain firsthand knowledge than by taking an avalanche safety course. It is also a very good use of time to read widely on avalanche safety, as there are a number of good books devoted solely to the topic, along with many case studies that make for grim but sobering reading. It has been shown by research that most victims caught by avalanches were either unaware of avalanches or safe route travel skills, or where they did know, they chose to ignore the warning signs. Taking an avalanche safety course won’t dent your time much but it could save your life.
Here are some things to think about when planning “where and if” you are going to go:
- Avalanches can be deadly
- Avalanches are caused by unstable snow, snow that has not bonded to underlying layers or to a hillside
- Most avalanches that impact the backcountry traveler are triggered by your own party
- Watch the weather! Rapid changes in wind, temperature and snow/rainfall may affect snowpack stability. Cold temperatures are more of a problem than warm temperatures, as they maintain an unstable snowpack
- A high percentage of avalanches occur shortly before, during, or after a storm
- Rapid snow accumulation increases danger; also, a foot or more of new snow is a concern
- Rainfall weakens or overloads layers and encourages them to slide
Check the avalanche forecast at Northwest Avalanche Center before you leave on your outing to obtain the current avalanche conditions. Other sources of current information are NOAA weather radio, the Forest Service, or a local ski area. Depending what the hazard is, find another destination (see Places to Snowshoe in this syllabus) or stay home!
If other than a Low Avalanche Hazard exists, it’s best to pick a safer route - one on a ridge top and slightly on the windward side, away from cornices. Or, travel out in a valley far from the bottom of slopes. Avoid slopes with cracks (avalanche fracture lines) or areas where you hear a “whumpf” sound.
Avalanches most often occur on slopes of 30 to 45 degrees, but be suspicious of any slope between 25 and 65 degrees. Convex (curving outward) slopes are generally more dangerous, but they can occur on concave slopes also. Leeward slopes, north-facing slopes, and in the spring south-facing slopes can all be dangerous. Some avalanche slopes are obvious - they may have debris that is noticeable from previous events and may be devoid of trees. In general, slopes with large rocks, trees and heavy brush are less avalanche prone, as these things help anchor the snow.
Should it be necessary for you to cross a potential avalanche slope, have the party cross one member at a time. Loosen your pack waist belt and sternum strap and remove ski pole straps so you can easily discard them if you get caught. Make swimming motions and try to stay on top of the moving snow as you work your way to the side of the slide. As the snow comes to a stop, try to make an air pocket in front of your face with your hands and inhale. Also, try to stick a hand or foot out of the snow; it might make you visible to rescuers.
Danger Rose
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. In the following example, the diagram indicates that a particular avalanche problem is thought to exist on all high elevation aspects and on north to west-facing mid elevations (colored grey), and that it is less likely to be encountered on other aspects and elevations (colored white)
Danger Scale Legend
The United States and Canada use a five-category estimation of the avalanche danger: Low, Moderate, Considerable, High and Extreme.
The North American Avalanche Danger Scale is a tool used by avalanche forecasters to communicate the potential for avalanches to cause harm or injury to backcountry travelers.
Avalanche Types
Avalanches have a wide variety of personalities. Avalanche Specialists use nine distinct characteristics or Avalanche Problem Types to better describe and communicate the avalanche conditions.
Dry Loose
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.
Storm Slab
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slab
Wind Slab
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Persistent Slab
Persistent Slab
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
Deep Persistent Slab
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Wet Slab
Wet Slab
Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.
Cornice Fall
Cornice Fall
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Glide Avalanches
Glide Avalanches
Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often preceded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
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