(Edited for Wallowa County by Roger Averbeck, Backcountry Avalanche Safety, Inc, and Charla Whiting, Wing Ridge Ski Tours LLC; original source, Northwest Weather and Avalanche Center at (www.nwac.us). Support for this avalanche safety information comes from Wallowa County Sheriff Search and Rescue, United States Forest Service, Wallowa Whitman National Forest, \Wallowa County Gamblers snowmobile club, Ferguson Ridge Ski Patrol, Eagle Cap Nordic Ski Club, Wallowa Alpine Huts, Wing Ridge Ski Tours and Back Country Safety Inc. This is the first of a two-part series.)
A snow avalanche is a complex and fascinating natural phenomenon. Experts on the subject aren't able to predict, nor do they completely understand each and every avalanche occurrence. It is important to recognize that the smallest avalanche can injure or kill people. In the United States, avalanches kill about 30 people each year.
Avalanche terrain exists throughout the Wallowas and close to Joseph in the Hurricane Creek, Wallowa River and Lostine drainages for example. There are large slide paths that cross the access roads to the Hurricane Creek and Lostine trailheads. Slide paths also exist across the hiking trails of all those drainages as well as many others in the Wallowas.
If you plan to recreate in the winter, pay close attention to the possible avalanche risk and avoid those areas if the avalanche danger is considerable or higher. Be aware that summer and fall hiking and equestrian trails were not designed and built to avoid avalanche terrain. Many wilderness trails cross avalanche slide paths.
Before you plan a trip into areas with avalanche terrain, you should prepare yourself with key information about the area and its hazards. For general winter recreation information in the Wallowa Mountains area, call the U.S. Forest Service Visitor Center in Enterprise (541-426-5546).
Local providers offer avalanche-specific courses. Wing Ridge Ski Tours (541-432-0712) offers a weekend avalanche awareness course each winter. Wallowa Alpine Huts (541-426-4887) also offers Level I and II avalanche safety training which are longer and more in-depth courses for frequent users of the back country.
The following general guidelines will help you recognize the presence and the degree of avalanche danger.
Awareness can help you and others avoid becoming an avalanche victim. Learn how to assess the terrain, weather, snow pack and the people in your group to decide when it is safe to go out in the backcountry. The simple red-yellow-green light method, described in next week's article, can help you make that decision.
Apply red-yellow-green light methodology to help determine whether terrain, weather, snow pack and human factors produce a go or no-go situation.
Frequency: The more you participate in winter activities such as skiing, snowshoeing, and snowmobiling, the greater your risk of being caught in an avalanche - prepare for and learn about dangerous situations.
Play it safe: Think about the changing weather, type of terrain and snow pack conditions around you, and constantly update your assessment of the avalanche danger. You can help minimize avalanche exposure to you and those around you by being cautious and alert. In the event of a burial, your preparedness may be the key to survival.
Types of Snow Avalanches Avalanches are caused by unstable snow conditions. Snow that is not well bonded to a slope, with underlying snow layers or other snow crystals, is categorized as "unstable snow." Weather, terrain, snow pack, and human factors also influence avalanche potential in unstable snow conditions.
Loose-Snow Avalanches start when unattached snow crystals slide down a slope. As it descends, this type of avalanche widens, forming an inverted V-shape and may become quite large as it gathers more surface snow. Depending on the size and conditions, it may also trigger the even more dangerous "slab avalanche".
Slab Avalanches start when a solid area of the snow cover ruptures or breaks away all at once, leaving behind a well-defined fracture line.
Avalanche Safety Basics Remember that avalanches don't happen by accident and most human involvement is a matter of choice, not chance. Most avalanche accidents are caused by slab avalanches that are triggered by the victim or a member of the victim's party. However, any avalanche may cause injury or death and even small slides may be dangerous. Always practice safe route finding skills, even if you think the snowpack is stable, and be aware of changing conditions.
Always carry avalanche rescue gear (a minimum of shovel, probe, and beacon). Learn and apply avalanche terrain analysis and snow stability evaluation techniques to help minimize your risk.
Avalanche danger rating levels issued by regional avalanche centers are only general guidelines.
The Wallowa Mountains are not covered by any avalanche forecast center. The nearest forecast center is the Payette Avalanche Center (www.payetteavalanche.org), 50 miles to the east. It issues an avalanche forecast for the west central mountains of Idaho, which has similar snow climate to the Wallowa Mountains. Distinctions between geographic areas, elevations, aspect, and slope angle are approximate and transition zones between dangers exist. No matter what the current avalanche danger, there are avalanche safe areas in the mountains.
Assessing the TerrainSlope Steepness - Avalanches most frequently occur on slopes of 30 to 45 degrees, but they may occasionally release from either gentler or steeper terrain.
Slope Profile - Dangerous slab avalanches are more likely to begin on convex (raised or curving outward) slopes but may also begin on concave (sunken, or curving inward) slopes. Short slopes may be as dangerous as long slopes, especially if an avalanche carries its victims into or over terrain traps like cliffs, trees, rocks, creeks or crevasses. Almost half of all avalanche fatalities result from slides running less than 300 feet (about 90 m) slope distance.
Slope Aspect - North-facing slopes may be slower to stabilize than slopes facing in other directions. South facing slopes are especially dangerous in the spring when heated by the sun. Leeward slopes face away from the wind are dangerous because this is where drifted snow collects and may form an unstable slab. Slopes that face the wind generally have less snow and are usually more stable.
Understanding the Snow PackSnow Depth - Large rocks, trees, and heavy brush help anchor the snow. Smooth, open slopes without these natural anchors are more dangerous. However, avalanches can start even among trees. When the snow depth covers natural anchors, additional snow layers will slide more readily. Snow depth also determines the rates of internal snowpack changes, like the development of weak sugar-like snow. Snow depth over an upper-level rain crust can also affect how rapidly snow layers weaken or facet above the crust when air temperatures are low - shallower depths mean more weakening.
Snow Layering - Make a habit of testing the layering and bonding of the snow structure by using ski or probe poles. Feel how the strength of the various snow layers changes as you push your probe through the snowpack. Test snow layering often as you move from area to area and use increasing caution if the resistance to a probe or pole decreases with increased depth. Snow structure and its stability can change significantly from slope to slope. Pay particular attention to very weak or very strong layers buried beneath the snow surface. The strong layers may act as a sliding surface for avalanches, especially if overlain by a weak layer. If you are uncomfortable about what you perceive, for example heavy snow over light snow, or the "whumping / collapse" of a snowpack around you, conduct further stability tests. Learn to dig snow pits and conduct shovel shear, compression, or Rutschblock tests.
Old Snow Surface - It is important to know the condition of the old snow surface when trying to assess developing snow stability. For example, cold snow falling on a hard, refrozen snow surface, such as a sun or rain crust, may form a weak bond and lead to a rapid increase in the danger.
Watching the Weather Changing Factors - Rapid changes in weather conditions (wind, temperature, snow / rainfall) can quickly change snow pack stability; therefore you need to stay aware of the weather and the trends in the weather at all times. The snow pack is very dynamic, and weather may change what was a stable snow pack in the morning into an unstable snow pack by afternoon.
Winds - Sustained winds of 15 mph or more, even during clear weather, may increase danger rapidly since such winds can quickly redistribute large amounts of loose surface snow. Snow plumes from ridges and peaks indicate that snow is being moved onto leeward slopes, which can accumulate ten times as much wind-blown snow as nearby sheltered valleys. This can quickly create dangerous slab conditions on leeward slopes and large changes in slope stability as you traverse from windward to leeward slopes.
Temperature - Cold temperatures (well below freezing) tend to maintain an unstable snow pack, while warmer temperatures (near or above freezing) allow snow to "settle," bond and strengthen more quickly, thus making the snow pack more uniform and stable. Prolonged cold air temperatures result in internal weakening of the existing snow pack through strong vertical temperature differences in the snow pack and associated development of new weakly bonded crystals (faceting or depth hoar). Meanwhile prolonged warm temperatures result in introduction of liquid water into snow layers that acts to lubricate and weaken snow pack bonds.
Storms - A large percentage of avalanches occur during or shortly after storms. Be especially aware of storms that start cold and then warm during snowfall.
Rate of Snowfall - Snow falling at the rate of 1 inch (2 - 3 cm) per hour or more increases avalanche danger rapidly, and allows underlying weaker layers less chance to safely accommodate the new load.
New Snow - Be alert to dangerous conditions with a foot or more of new snow. Remember that new snow depth may vary considerably with slope elevation and aspect.
Wet Snow - Rainfall on new snow can rapidly weaken surface snow and overload buried weak layers, sometimes causing avalanches to occur almost instantaneously with the start of rain. Rain may also percolate through the snow until it reaches an ice layer or a layer of smaller grains. It can then pool or lubricate the snow near or within this layer and produce large, wet-slab avalanches. During sustained heavy rainfall, a series of avalanches may occur on the same slope as progressively deeper snow layers are weakened or stressed.
Wet-slab avalanches are also produced in the spring by strong sunshine or radiation through clouds that melt and weaken the snow cover. When a warm day is followed by clouds overnight that prevent the snow surface from refreezing, dangerous avalanche conditions may develop the next day when temperatures increase, and larger deep slabs may result.
Clear weather - While clear, calm skies during winter often allows for excellent recreating opportunities and great visibility, it may also produce surface hoar, the ice equivalent of dew. Fragile ice crystals may be deposited directly on the snow surface during clear nights, and may provide very weak attachment to subsequent new or wind transported snow. In such instances, very sensitive slab slides are possible.
Accounting for Human BehaviorWithin the basic triangle of snow pack, weather, and terrain lies the subjective human factor. All too often people ignore factual information, and make decisions that are neither prudent nor wise and are based on human issues. Some of these human considerations include:
Attitude - Overconfidence, ego (pride or greed), stress, conflict, impatience, euphoria, hormones, desire for first tracks or rush to the summit.
Physical - Fatigue, cold, wet, schedules, equipment, injury, "gizmo reliance."
Group - Poor communication, poor planning, time management, tunnel vision, incorrect assumptions, disparate skill or physical levels, "herding instinct" (safety in numbers), "lemming instinct" (always follow), "horse syndrome" (head back to the barn), goals.
Skill level - Do avalanche hazard assessment skills match travel skills?
Other factors - Good weather (increased risk acceptance); familiarity smugness; positive reinforcement, it-won't-happen-to-me beliefs.