Outdoor Skills: Ted Kerasote How to Predict an Avalanche When outdoor recreation was less mechanized, only skiers and mountaineers were killed in avalanches. Now anyone who can press a starter button and steer can get into trouble. During the last five winters, 27 snowmachiners have perished in avalanches in the United States. Hunters, too, are not immune. Since 1971, 14 have been swept away by avalanches in the United States; four of them died. The chances of surviving a winter outing can be improved by following the lead of avalanche-control workers, who dig a snow pit before traveling questionable slopes (avalanches commonly run on slopes between 25 and 55 degrees). A snow pit shows the history of the snow pack--the weak, unconsolidated layers, known as depth or surface hoar, and the various sliding surfaces created by rain or snow crusts. Noting these dangerous layers in the wall of the pit, you may elect a less steep route. A snow pit should also be combined with a mechanical shear test known as the Rutschblock. The test involves loading a large block of snow with the weight of one person and increasing the load in several stages until the block slides. This test gives a good indication of a slope's stability. Every winter backcountry traveler should know how to perform it. The Pit: Choose a spot with the same aspect, elevation and angle (30 degrees is preferred) as the slope you intend to cross. Make sure the test slope has a minimal runout, so if you start an avalanche the consequences won't be dire. Dig a pit about seven feet wide, four feet back uphill, and down to the ground. Do not disturb the uphill portion of the pit, where you will conduct the Rutschblock test. With a hat or mitten (ideally a soft-bristled paintbrush), smooth the upper, vertical wall of the pit with horizontal strokes. This will reveal the sedimentary snow layers. Test the relative hardness of each layer by trying to push your fist, four fingers, one finger, a pencil or a knife into it. A layer that permits entrance of your fist is very soft; four fingers, soft; one finger, medium; a pencil, hard; a knife, very hard. A hard layer lying on top of a soft layer can indicate slope instability, but so can a soft new layer on top of a sliding surface, such as an ice crust. The Layered Effect Judge the stability of the slope by test ing the hardness of the snow layers and then determining how stable they are. First, dig a pit seven feet wide and four feet uphill. Examine the stratifications as noted in the text. Then isolate a block of snow uphill from the pit and conduct a Rutschblock test, which will indicate whether or not a similar slope can be traveled safely. The Test: To see which layers will fail under a load, conduct the Rutschblock test. From the pit wall, cut a block 6 1/2 feet long in front and about 4 1/2 feet uphill. Use a shovel or skis. If the block shears off on some weak layer and slides into the pit while it's being excavated, this is graded a 1 and means the snow is extremely unstable. If the block remains in place, continue loading and grading as follows. Load 2: One person on skis--for snowmachiners, one person on foot--steps carefully onto the block from above. Load 3: The person adds weight by performing a rapid knee bend. If the block shears at loads 2 or 3, stability is poor. Load 4: The person jumps once. Load 5: The person jumps twice. Failure at loads 4 or 5 indicates fair stability. Load 6: A person jumps onto the block from the slope above, without skis. Load 7: Repeated jumping. Failure at load 6 or no failure equals good stability. Failure at load 7 or no failure equals excellent stability. These results can then be used to decide whether to traverse a slope of similar aspect and angle. Remember that a stable Rutschblock test does not mean the actual slope to be traveled won't slide. Precautions: Everyone in the party should carry an avalanche transceiver, which is a wallet-sized electronic device that transmits and receives radio signals. The transmitted signal greatly increases the chances of an avalanche victim being found quickly. While traveling, everyone in the party wears a transceiv er around the neck and keeps it in the "transmit" mode. If someone is buried, those on the surface switch their transceivers to the "receive" mode and search in a grid pattern across the snow. The nearer one is to the victim, the louder or larger the signal in the receiving unit becomes. Transceivers should never be stored in a backpack or on a snow machine because avalanche victims commonly become separated from their equipment. The Pieps 457 transceiver costs $250 (available from Black Diamond; 801/278-5533). For details on transceiver use and avalanche rescue, read The Avalanche Handbook by David McClung and Peter Shaerer ($19.95; available from The Mountaineers, 206/284-6310). ⌐ 1997 The Hearst Corporation. All rights reserved.