The technique of snow craft is identical in its principles with that of ice craft. The upright balanced movement, the management of the rope, turning, anchoring, etc., are the same, or only slightly modified. Only points of detail, therefore, need be mentioned which are peculiar to the different qualities of snow surface. In certain cases, such as bridges and cornices, both snow and ice are in question, and the notes are then supplementary to those made under general ice craft.
To make snow steps is a matter of muscle and rhythm; to use them, one of balance and endurance; but to know how to avoid making them and where not to make them is the science of snow craft. We may learn to identify snow states by description: nothing but experiment can teach us how to deal with them.
We may classify the states of snow under many heads; but we are only practically concerned with three points: which of these states are pleasant, which are unpleasant, and which are unsafe to walk upon. Of most importance is it to be certain which states are likely to be unsafe, and to be able to recognize their presence beforehand.
Under Reconnoitring some suggestions are made as to the signs by which snow states may be interpreted from a distance, and some of the certainly unsafe ones consequently avoided in anticipation.
As to whether the state on a particular day will be pleasant or unpleasant, the weather of the day, the hour and the angle of the snow can tell us much. The final test must always be by touch.
Some Characteristics and Countermoves.
Snow lying at above an angle of 20 degrees may slide whenever its support is not equal to its mass. Its support comes either from behind, the rock, ice or snow surface upon which it rests; or from its quality, the cohesion of its particles; or from below, the angle and mass of the subtending snow slope. In deciding about its safety we must take all those three points under our inspection. Of its sub-surface we know something if we can ascertain the lie of the rock strata or detect the presence of ice. Of its quality and mass we judge by surface signs and our recollection of the weather. Of its support from below we judge by the angle at which it lies; not only by the angle of a specimen section, but the angle of all sections of the slope below.[17]
Snow lying at easy angles, exposed to the directer rays of the sun, will usually be soft; and while we may be able to mince over its night crust before sunrise, we do well to avoid its possibilities of purgatory on our return later in the day. Snow on south and south-east faces for the same reason is the more to be respected, and its earlier deterioration must be accepted without resentment.
If a strong wind has been blowing, the snow on the sheltered side of a peak will be the softer and the more likely to avalanche. Snow on a sheltered face becomes loosened in fibre by the balance between the air-currents, whereas, on the windy side, it will get blown off or blown superficially hard.
If there has been Föhn in the wind, the snow will be untrustworthy all round. Föhn has the insidious quality of disintegrating snow through all its depth; it may appear to have affected the surface relatively little, but it will have reduced the under-snow to slush. This is the most perilous of avalanche states.