Snow cannot lie at anything like the angle at which it often appears to lie when seen in face. From the presence of snow, in fact, much can be argued as to the generally mild angle of the mountain face on which it lies. Except in narrow couloirs, where it is supported by the walls, snow does not lie permanently above or even up to an angle of fifty degrees. Most big snow slopes are considerably less. The broader the face on which it lies, usually the less the real angle of the snow.
The fact that a big snow peak presents a continuous slope of snow to its summit is evidence that the mean angle of the ascent is not great, otherwise the even accumulation could not have proceeded. In prospecting a new mountain, therefore, however tempting its rock face or ridge may be to a modern climber, its snow side, if it has one, may be assumed to offer the inclination of easier ascent. And this more particularly if the snow slopes face towards the south, where the snow would naturally adhere least to the face.
Interruptions to climbing on such snow faces, whether as steeper slopes of snow or as ice walls (such as it is well to note beforehand), are at once apparent from their different shading if the snow slopes are inspected when the sun is overhead.
The inclination of a hanging slope of snow always appears still more exaggerated as seen from in front if it lies on the face of what is mainly a rock peak. We have in such case to discover if the snow is lying on ice, or only forms a coating to the rock. If it is on ice, the lower edge of the slopes, where the snow runs out on to the rock, will generally betray a rim or broken wall of ice. To judge of the quality of such a snow surface, and of the strength of its attachment to its ice or rock sub-surface, the slopes below it must be examined, and snow, stone or water furrows looked for. By the crumpled or the clean appearance of the edges of the slope itself, where it touches the rock walls on either side of its descending fan, much can be learned of its past transmutations and present condition.
Long or short spits of lighter snow, running up against darker snow or ice, are the retentions of later falls, and are indications of uneven angles of surface. They betray the presence of bulges or ribs below, and, besides their promise of easier progress on slopes where the general surface may be frozen hard or over-steep, they give us by their contrast a further basis for our estimate of the actual inclination.
The presence, the shape, and the number of cleavages or crevasses in a slope of ice or snow are a further guide to our estimate. A certain type of crevasse is only found on slopes lying at an angle of about forty-five degrees.
We may get additional evidence, in cases of doubt, by waiting for the sun to throw the shadow of another peak or shoulder upon the slope. When the sun and the interruption are located, the distortion of the reflection will allow of an approximate estimate of the angle of the snow slope.
Faces or ridges of mingled rock and snow, and surfaces interrupted by the intrusion of any detail, be it only of a shadow or tint, are always easier for the experienced eye to estimate, in angle and character. Where we have rock and snow or light and shadow in contrast, practice in the reading of snow and ice surfaces, and in the rules that govern their angles of inclination and attachment, and practice in the interpretation of the details of rock structure, become mutually and comfortably corrective.
Snow Cornices.
Cornices form against the wind, not with it. The contrary is sometimes stated; but the error is possibly due to the fact that irregularities in the configuration of a ridge often produce back eddies in a cross-wind. If the prevailing wind is snow-bearing, and across, a snow-bearing back swirl may build a small cornice on the sheltered side of a ridge. Such a small cornice would appear to have been formed with the prevailing wind: actually it would have grown against its return eddy. A wind blowing along (not across) a serrated ridge may similarly produce very small cornices facing either way on the ridge, and apparently at right angles to the prevailing current, owing to some tower or curve on one side or the other having created an inward and upward cross-eddy, and a shelter from the main-current in which the snow-laden eddy can work. Large cornices facing either way on the same ridge, and the double cornices, are produced by a shift in a snow-bearing cross-wind to the directly opposite quarter. If we find ourselves on a corniced ridge when a strong wind, and especially a strong wind from a warm quarter or with Föhn in it, is blowing against the back of big cornices, i.e. from the opposite direction to that from which the snow-bearing wind was blowing which formed the cornices, we have to be even more careful, if that be possible, in dealing with them, as such a wind will loosen their attachment and magnify the suddenness and the size of their collapse. A cornice will always form more easily on the summit of a sheer or abrupt wall, which creates a strong upward eddy in a wind blowing against it, than upon a more gradual or snow-rounded inclination which offers less resistance to the current and less ‘catch’ to its snow burden. For this reason, upon a summit or a ridge which has, as so often is the case, one more gradual snow side and one rock side inevitably steeper, we must be prepared to find cornices overhanging the rock face, larger if produced by a wind-shift, lesser if by a back eddy, even though the prevailing wind has blown regularly upon the opposite snowy face, and should have relieved us of the necessity of caution by its failure to develop cornices on that side.