ROUTE FINDING IN AVALANCHE TERRAIN
By Dale G. Gallagher
When traveling in back country during the winter, for work or pleasure, you must find a route that is safe from avalanches. If you are away from ski areas or highways, you must determine the current avalanche hazard. You also need to keep foremost in your mind that, when you are in the back country, help will undoubtedly be several hours away. In winter emergencies, minutes are often the difference between survival and death.
PRIOR TO THE TRIP
Adequate planning and review will help make the trip successful. Weather data should be gathered--past, present, and predicted. Several sources are usually available, such as the National Weather Service Offices, radio and TV stations, newspapers, and the local Snow Ranger. Pay particular attention to long-range forecasts.
The factors that contribute to avalanches should be-reviewed, such as wind, new snow, old snow, temperatures, and settlement. These should be analyzed against the past and present weather and snow conditions. Keep in mind that avalanche hazard varies from one climatic zone to another. (See diagram, Appendix -i-.)
When packing, remember emergency equipment such as a sectional probe or skadi, emergency ski tip, avalanche cord, first aid kit, as well as the basic essentials.
DURING THE TRIP
*Throughout your trip, you need to be observant. Look at the terrain, the snow, and the weather.
*Slide paths may be obvious, such as swathes through timber, gullies, or open slopes. However, scattered timber or small openings can also be avalanche areas. Short avalanches are killers--42% of the fatalities occur in slides that run less than 300 feet.
*Consider the conditions of the old and new snow. How deep is the old snow and what was its surface? How deep is the new snow, what kind is it and what has it been doing? Is it slowly settling or does it have cracks over the surface? Look for avalanches that have run naturally. Note the direction this slope faces and the kind of avalanche it was.
*Watch how the snow reacts under skis or snowshoes-or snowmobiles. Do you see localized breaking of the snow surface or running cracks? Running cracks indicate the snow is tending to form slabs.
*Has the wind been drifting the snow since the last storm?. If so, try to analyze which slopes have been loaded.
*And, during your trip, watch for even the slightest weather changes--temperature, wind, clouds, etc., can indicate changes that may affect your trip.
Safe Time to Travel
*The safe time to travel will vary.
*During early and mid-winter, rapid temperature changes occur early morning and late afternoon. Travel is best during mid-day. However, in late winter, the mid-day and afternoon melting provides lubrication, which increases hazard. Travel should be done early or late in the day.
*If a storm sets in, travel should be during the first few hours, or bivouac should be made until the hazard has abated. The highest danger is during the storm and immediately afterwards. If cold temperatures are persistent, high hazard may exist for several days. Even in summer, at higher elevations, prolonged snowstorms may result in avalanche hazard.
*Avoid known avalanche paths. If it is necessary to travel when there is a suspected hazard, it is advisable to:
1. Stay on the windward side of ridges. If available, exposed rocks or wind scolloped snow are the safest routes. (See diagram, Appendix -ii- and -iii-.)
2. In a "U" shaped valley, stay as far away from slopes with avalanche potential as possible. (See diagram, Appendix -iv-.)
3. In a narrow or "V" valley, stay high on the slope, as close to fracture (crown) zone as possible. (See diagram, Appendix -v-.)
4. Stay in dense timber. Avalanches do run through scattered timber. (See diagram, Appendix -vi-.)
5. Stay on rocky ridges that parallel avalanche paths, providing they protrude above the snow surface enough to avoid the snow sliding on either side of them. Know the terrain, since there may be additional avalanche paths above these ridges that will inundate them. (See diagram, Appendix -vii-.)
6. Stay off cornices. The view may be great, but you nay also experience a sudden "let down" feeling. Cornices may fracture into two different areas. (See diagram, Appendix -viii-.)
A primary fracture breaks near the lip and is usually a result of the buildup from the last storm. Secondary fractures occur further from the lip and are caused when the mass (weight) of an entire cornice exceeds the snow strength. Failure may occur at once, or a rupture crack (like a small crevasse) may develop and gradually widen over several days or weeks until the failure occurs. The crack may be hidden by a thin snow bridge.
7. Stay to the downhill side of crevasses on a glacier. A small avalanche can sweep a person into a crevasse and bury him deeply.
If you find it necessary to traverse the accumulation zone of an avalanche slope, take these precautions:
1. Ask yourself:
a. "Will it probably slide?"
b. "What will happen if someone does release it?"
c. "What will we do then?"
2. Remove or loosen equipment such as ski pole straps, packsacks, etc.
3. Expose only one person at a time to danger. Only one person should be on an avalanche slope at any one time. Others in the party should watch him to establish a "last seen" point if he is caught.
4. Stay as high as possible -- the closer you are to the fracture line (crown) the better chance you have to survive if the avalanche releases with you.
5. Use an avalanche cord or, better yet, an electronic signal sender such as the SKADI.
6. Use natural protection in your route. Rock outcrops, tree clumps, and other "islands" in the snow offer some protection.
7. Do NOT assume a slope is safe if it doesn't slide after the first man has crossed it. The accident reports prove that an avalanche can release after several people have already safely crossed it.
Remember, avalanche paths are the most dangerous routes and should be used only if there is no other feasible route.
-Know the weather
-Know what causes avalanche hazard
-Be properly equipped
-If you must travel in avalanche areas, choose your route very carefully
1. Most people caught in avalanches started the slide themselves.
2. Small avalanches kill 42% of the victims.
There is no magic formula--
--Take time to think
--Use good Judgment
--If your sixth sense says NO, then don't GO.
FEW O-PAC HOT
F -Factors contributing to avalanches
E -Equipment for emergencies
W -Weather past, future, and current
H -High on the slope
0 - One at a
T - Time
Predominate avalanche types and applicable forecasting methods in the
mountainous areas of the western United States. (1) Generally deep and stable
now covers. Extensive surface avalanching, with possibility of melt or rain
throughout the winter. Avalanching forecasting by meteorological observations.
(2) Often stable snow covers, extensive surface avalanching, melt or rain rare in
mid-winter months. Forecasting largely by meteorological observations.
(3) Shallow, unstable snow covers with depth hoar formation common and climax,
hard slab avalanches frequent. Forecasting largely by snow structure analysis.
(4) Conditions of (2) and (3) may overlap, with one or the other usually
predominating in a given winter. Forecasting actively combines meteorological
and snow structure observations.
E. R. LaChapelle