Publications

AMC Outdoors, November 2000

By Michael Lanza

Three years ago this month, two hikers started up the headwall of King Ravine, on Mount Adams in New Hampshire. They never made the top. The lead hiker triggered an avalanche that swept him 200 feet down the steep slope, leaving all but his face and one arm buried.

Instead of immediately searching for his partner, the second hiker — who was nearby but untouched by the avalanche — tried unsuccessfully to find help. In a bizarre twist to the story, the victim managed to dig himself out of the avalanche debris, and both men spent the night on the mountain unaware of the other's condition or whereabouts. The next morning, they walked out to the road just three hours apart.

The story is unusual for having a happy ending, but not for the fact of the avalanche. Avalanches occur regularly in the steep ravines and on above-treeline slopes of the Northeast's highest mountains. Occasionally they claim victims, usually backcountry skiers in places like Tuckerman Ravine or the Gulf of Slides on Mount Washington. And with increasing numbers of winter hikers and snowshoers seeking high ground in the Northeast, avalanches pose a risk to more and more winter enthusiasts. Though it's important to learn all you can about avalanche safety, nothing substitutes for thorough, in-the-field training from a knowledgeable instructor.

The Dope on Slope
When an upper layer in the snowpack fails to bond well to the layer beneath it, the upper layer's weight and the angle of the slope sometimes conspire to send that upper layer sliding downhill. In a loose-snow avalanche, warm sunshine or a person crossing a slope causes the snow's surface to slough off in a slide that may grow larger and travel a long distance.

In a slab avalanche, a broad area of snow abruptly breaks loose, leaving behind a distinct fracture line. These are the most dangerous avalanches because they often release while someone is atop the slab, accelerate quickly, and carry tons of debris hundreds or thousands of feet at speeds up to 80 mph.

The first rule of avoiding avalanches is to know how to read the slope angle. Snow slides on slopes angled between roughly 25 degrees and 55 degrees. If they're less steep, snow cannot slide; if any steeper, not enough snow accumulates to slide. Avalanches occur rarely on slopes below 30 degrees — the steepness of most ski resort black-diamond trails — and most frequently on 38-degree slopes. Unfortunately, backcountry skiers usually gravitate to slopes between 25 and 40 degrees. Slope angle is very difficult to estimate visually, so use an inclinometer or a compass that measures angle.

Watch the Weather
Weather reveals much about avalanche hazard. High winds, an abrupt change in temperature, and heavy snowfall all create conditions ripe for avalanches. In the Northeast's alpine zones, wind is the primary culprit; winds from the west sweeping across Mount Washington, for instance, dump huge amounts of snow in its east-side ravines.

Winds 15 mph or greater transport snow to the lee side of slopes and ridges, "wind-loading" them and quickly forming a dangerous surface slab. Following a major snowfall, snow can remain unstable for a day or more. Periods of clear, very cold nights create an unstable layer in the snowpack that can cause a slide.

The aspect of a slope, or the compass direction it faces, affects avalanche hazard by determining the amount of sunlight the slope receives. Sun on southerly slopes hastens snow consolidation — giving it a fairly consistent density and bonding layers together — making them safer than north-facing slopes in midwinter. But in spring these same southerly slopes soften and become more prone to loose-snow slides. Northerly slopes consolidate slowly — promoting instability in midwinter but greater stability in late winter and spring. On a given day, a slope at one aspect may be entirely safe while a different aspect can be highly hazardous.

Getting Around
Even after determining that avalanche hazard is low, you should be careful. For starters, know when you're in potential avalanche terrain by looking for clues to where avalanches have occurred. A sharp fracture line indicating where a slab released, and the blocky snow of avalanche debris, are clear evidence of a slide. Gullies devoid of large vegetation, or stunted trees leaning downhill, indicate frequent avalanche activity. Those places may or may not be safe to cross — you have to know how to evaluate their avalanche risk.

There are a variety of ways to evaluate avalanche hazard on a slope, from thrusting a ski pole (handle first) into the snow, to conducting a rutschblock (or stuffblock) test, which consists of digging a snow pit to test avalanche hazard on a particular slope. The basic idea is to look at the snowpack for dense hard layers atop hollow layers — prime avalanche conditions. Evaluating hazard is complex, however. Learn the skill from someone who knows it, and practice it frequently.

Keep the following guidelines in mind when traveling in the winter backcountry:

• Unstable slabs may settle with a dull whump under your weight before a slab avalanche releases. That's a strong warning of unstable snow. If you hear a whump on a slope steeper than 25 to 30 degrees, or see cracks in the snow, either backtrack or follow the lowest-angled terrain possible to safe ground.
  
  
• Travel between "islands" of safety like rocky or densely forested ridges, in the middle of broad valleys, and on the windward side of a snowy ridge. Frequently consult a detailed topo map (like the 1:24,000-scale USGS quads) to avoid traveling below potential avalanche slopes that may be obscured from view.
  
  
• Relatively safe low-angle slopes may have short, steep bulges, or rolls, where slabs can release. Don't pass over their crest or directly below them. Avoid passing below cornices — those wavelike lips of snow created by wind, usually on ridge crests — unless you're confident they are stable. In the ravines of the Northeast, falling ice presents a similar hazard, especially when temperatures rise above freezing. Falling ice may not trigger an avalanche, but it can be just as deadly.
  
  
• When crossing gullies, bowls, and other avalanche terrain, move one at a time between islands of safety, and watch the person ahead of and behind you in case he or she gets caught in a slide.
  
  
• Avoid traveling directly above or below another person. Ninety-five percent of victims are caught in slides triggered by themselves or someone nearby — not in spontaneous slides. Spread out to reduce the number of victims.

If you're caught in a slide, try to escape off the side of it before it accelerates, or grab a tree, or swim atop the slide. When you feel it slowing down, punch a hand upward to help others find you. Clear an air pocket in front of your face if you're buried.

If you see someone caught in an avalanche, try to keep your eye on the victim until the avalanche stops, then look for clues to her whereabouts, like gear or clothing. Never abandon an avalanche victim to go for help — because most die of suffocation, the only chance of surviving an avalanche is being rescued by people nearby within minutes.

Everyone going into avalanche terrain in winter should carry a portable, lightweight shovel; a probe (or probe ski poles); and a transceiver, and know how to use them. Practice searching for a victim by burying a transceiver (in a plastic bag) and taking turns looking for it.

It's the rare and fortunate soul who survives an avalanche. Know when to go into the backcountry. Before heading out, check the weather forecast and avalanche report, if one is available. In the backcountry, conduct your own evaluations of avalanche hazard throughout the day. If conditions look scary, stay home with a mug of hot chocolate and watch a good backcountry skiing video.

—Michael Lanza is author of The Ultimate Guide to Backcountry Travel, from AMC Books.