Routefinding On Snow
By Don Graydon.
Mountaineers read the snow surface and terrain features to determine a safe, efficient route. Dangers often lie beneath the surface: moats, creeks, or glacier crevasses hidden by a thin snow cover. Minimize the frustrations and dangers of snow by studying the medium. Mountaineers let the snow work for them.
The best snow is snow that is safe from avalanche and that will comfortably support your weight for easy stepkicking. Such snow exists, but you have to seek it out. Location of the best snow varies from day to day, even from hour to hour. If the snow is slushy in one spot, or too hard or too crusty or too something, look around: there may be better snow a few feet away.
Tips for making the best use of the snow surface:
- Find patches of firmer snow on a slushy slope by walking in shade or using sun cups as stairs.
- Find patches of softer snow on a slope that is too firm for good stepkicking.
- When the going is difficult, detour toward any surface with a different appearance and possibly more comfortable support.
- Use a different descent route if necessary to find the best snow.
- If you want a firmer surface, look for dirty snow, which absorbs more heat and therefore consolidates more quickly than clean snow.
- Remember that south and west slopes in the Northern Hemisphere, bearing the heat of afternoon sun, consolidate earlier in the season and quicker after storms. They offer hard surfaces when east and north slopes are still soft and unstable.
- Get an early start after a clear, cold night that follows a hot day, in order to take advantage of strong crusts on open slopes before they melt.
- Beware of the hidden holes next to logs, trees, and rocks, where the snow has melted away from these warmer surfaces.
Major terrain features present both obstacles and opportunities. Some you use, some you avoid, but they all have to be reckoned with.
- Couloirs: Angled gullies that provide a main avenue for all mountain climbing. They can hold the key to upward progress because their overall angle is often less than that of the cliffs they breach, offering less technical climbing.
- Pass through couloirs early in the day, when the snow is solid and rocks and ice are frozen in place.
- Couloirs can become increasingly nasty the higher they are ascended. They present the climber with extreme steepness, moats, rubble strewn loosely over smooth rock slabs, thin layers of ice over rock, and cornices.
- Finding the correct couloir on a particular route can be a challenge because they often look alike and there may be many different couloirs in the area.
- Ridges: Free of rockfall and avalanche hazard, ridges can be the best choice for a long ascent in a region of moderate to heavy snowfall.
- Routefinding on a ridge top is generally easier than other places on the mountain.
- You can usually find a safe way to retreat.
- Ridge routes take the full brunt of wind and bad weather.
- The most significant hazard of ridge routes is presented by cornices.
- Cornices: Present significant hazards. Find out whether the ridge you are on conceals a cornice.
- The shape of a ridge crest helps determine the extent of cornice-building. A ridge that slopes on one side and breaks into an abrupt cliff on the other is a good candidate for a gigantic cornice. A knife-edge ridge or one gentle on both sides will typically have only a small cornice, if any at all. Exceptions certainly exist on major alpine peaks with extreme conditions.
- Approaching from windward, a cornice gives little sign of its presence; it appears to be a smooth snow slope that runs out to meet the sky.
- Approaching from leeward, you can't miss a cornice. If you doubt the stability of the cornice, stay among trees or on spur crests as you travel below it.
- Bergschrund: The giant crevasse found at the upper limit of glacier movement, formed where the moving glacier breaks away from the ice cap.
- The downhill lip of the bergschrund can be considerably lower than the uphill edge, which may be overhanging.
- Sometimes the bergschrund is the final problem of the ascent.
- Moat: The gap that separates a snowfield from its rock borders, formed when the snow melts and settles away from the warmer rock.
- Crossing a moat at the top of a snowfield can be as tough as getting past a bergschrund.
- The main difference between a moat and a bergschrund is that the far wall of a moat is rock instead of snow.
- Rockfall: Snowfields and glaciers are prime targets for rockfall from bordering walls and ridges-especially on volcanic peaks, where the rock is often rotten and unstable. Reduce rockfall danger by wearing hard hats in hazardous areas and by timing climbs for less dangerous periods.
- Early-season outings usually face less rockfall than summer climbs because snow still helps cement loose rock in place.
- Follow the rule of thumb, "early on and early off." The greatest hazard comes in the morning, when sun melts the ice, and in the evening, when meltwater expands as it refreezes, breaking rocks loose. Nighttime cold often freezes rock in place and prevents most rockfall; direct sun melts the bonds.
A good routefinder uses a variety of tools to stay on route or reach a destination, including a compass, a map, an altimeter, wands, cairns, the sun, and visual landmarks. The creative use of several methods becomes especially important when visibility is poor.
- The thin bamboo wands topped with tiny flags are left to mark the return route. Also use these to mark points of danger (such as moats and crevasses), changes in direction, the boundaries of safe areas for unroped walking in camp, and the location of buried supplies (caches).
- An altimeter helps determine your progress and location when you use it along with a topographic map and compass, especially above timberline on a large snowfield with few natural features.
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