单选题
Avalanche and Its Safety
An avalanche is a sudden and rapid flow of snow, often mixed with air and water, down a mountainside. Avalanches are
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the biggest dangers in the mountains for both life and property.
All avalanches are caused by an over-burden of material, typically snowpack, that is too massive and unstable for the slope
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supports it. Determining the critical load, the amount of over-burden which is
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to cause an avalanche,
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a complex task involving the evaluation of a number of factors.
Terrain slopes flatter than 25 degrees or steeper than 60 degrees typically have a low
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of avalanche. Snow does not
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significantly on steep slopes; also, snow does not
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easily on flat slopes. Human-triggered avalanches have the greatest incidence when the snow"s angle of rest is
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35 degrees and 45 degrees; the critical angle, the angle at which the human incidence of avalanches is greatest, is 38 degrees. The rule of thumb is: A slope that is
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enough to hold snow but steep enough to ski has the potential to generate an avalanche, regardless of the angle. Additionally, avalanche risk increases with
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that is, the more a slope is disturbed by skiers, the more likely it is that an avalanche will occur.
Due to the complexity of the subject, winter travelling in the backcountry is never 100% safe. Good avalanche safety is a continuous
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, including route selection and examination of the snowpack, weather
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, and human factors. Several well- known good habits can also
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the risk. If local authorities issue avalanche risk reports, they should be considered and all warnings should be paid
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to. Never follow in the tracks of others without your own evaluations; snow conditions are almost certain to have changed since they were made. Observe the terrain and note obvious avalanche paths where plants are
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or damaged. Avoid traveling below others who might trigger an avalanche.