Nonetheless we can arrive at some practical ideas about avalanches, just as we get along with electricity with out fully understanding its nature. Most avalanches originate on slopes of 80 degrees or more, so we can consider this factor a constant. The variables are the condition of the snow and the weather. Forty-three years ago observers of the U. S. Weather Bureau, after a study of a disastrous series of avalanches in the Northwest, made an acute observation which has become the basis for modern techniques of avalanche hazard forecasting. In brief, the observation is that the hazard depends not only on the quantity of snow but also on the manner in which it fell.
Snow comes in a variety of forms, from the familiar crystal flakes to pellets.
In size the particles range from flakes as big as a silver half dollar to motes barely visible to the naked eye. The moisture content varies from less than one twentieth to more than one half of an inch of water per inch of snow. The consistency of snow ranges from a dry, flour-like powder to a gluey slush. All of these variations affect its stability. And it is constantly changing from one state to another.