The Alps

by Sir William Martin Conway

Let us briefly consider the stages of formation and decay of a single group of mountains, not volcanic. If we go back to the very start, we may imagine their future site occupied by a plain. The slow cooling and consequent shrinking of the world involves the wrinkling of its surface, and the position of the wrinkles is determined by a variety of forces, as yet little understood, with which we need not concern ourselves. Suffice it to assume that our plain occupies the position of the next coming group of wrinkles. A single range or line of mountains hardly exists in the world outside of the commonplace cartographer's mind. Old-fashioned maps used to represent mountains by a kind of caterpillar meandering about on them, and thus gave currency to the notion that mountains are generally arranged along a single line—a notion, by the by, that (in the minds of politicians negotiating boundary treaties) has been prolific in costly disputes and misunderstandings.[2] Mountains generally exist in rows of more or less parallel ranges intricately jointed together, and they do so because, when the wrinkling that caused them began, it did not begin with a single wrinkle, but with a row of wrinkles, such as a soft tablecloth makes on a smooth table when parts of it are moved toward one another.

[2] Witness the Argentine and Alaska boundary disputes.

Thus the first sign of a mountain range will be a series of undulations upon the surface of the supposed plain. These undulations will be roughly parallel to one another. We call the direction of their parallelism the strike of the ranges. From the moment the wrinkling movement begins, a set of forces is put in operation tending to level the wrinkles and fill up the hollows or valleys between them. These are the forces of denudation. People often vaguely speak as though mountains were first elevated to their full height and then only began to be pulled down; but of course the process of mountain sculpture is due to the simultaneous operation of the elevating and destructive forces. Every mountain is being pulled down in the very process of its elevation. It grows only because it is elevated faster than the destructive forces avail to level it. For all we yet know, some of the mountain ranges which seem most rapidly disintegrating may, in fact, still be growing. No one has yet divided the mountain ranges of the world into those which have not yet reached and those which have passed their maturity. When that has been done we shall doubtless find some clearly marked difference in aspect between them which now we do not know enough to recognise. The visible difference once discovered, the two groups will raise different kinds of emotion in the man who sees them. He will note the aspect of growth in one set and of decay in the other, and will be correspondingly affected, as we all now are by the young leaves and buds of spring and the fruits and faded foliage of autumn. Sad folk will love the fading and sanguine folk the growing hills. There will arise a new subject for poets and a new group of similes for preachers and moralists. In this way also science enlarges the material of art.

But we must return to our nascent mountain group, as yet a mere series of parallel wrinklings, higher here, lower there, with lines of depression between them. Rain falling will need to drain away, and in doing so will form pools in hollows, and will run along the furrows till it reaches the open country and can turn away. Thus the first streams of a nascent group of mountains follow and do not flow across the strike. Only the rivulets that actually flow down the slopes will flow in a direction perpendicular to the strike, and will be tributaries to the main lines of drainage that flow along the strike.

STORM CLOUDS OVER THE LAKE OF THUN

Looking up the Kander Thal. The Niesen on the right.

The mountains are rising steadily as the millenniums of years pass on. The rain keeps falling on them, and as they grow higher the snows of winter first, and later of all the year, whiten their summits and gradually descend upon their slopes as the summits reach higher and higher aloft. If the rain always fell uniformly over the whole area, and if the ranges were of rock, homogeneous like a great lump of plaster, equally strong in every direction—if such were the case, each range would remain approximately symmetrical on both sides, and the crest of it would lie evenly between its two flanking troughs. But that is never the case. The rain-bringing winds are sure to come more frequently from one side of the mountain area than from the other. The wet quarter will be the east or the west or the south-west, as the case may be, and more moisture will be precipitated and consequently more denudation effected by it on one side of the ridges than on the other, with important sculpturing results as we shall presently observe.

We may best regard the rising mountain area as a plateau with a wrinkled top, such a plateau as Tibet, for example. As time advances the plateau will present ever loftier walls to the outside world, but the undulations within will not greatly develop by any directly wrinkling process. It is not the wrinkling that splits the plateau up into ranges, but quite other forces. All that the wrinkling does is to give to those forces their first direction. The interior of Tibet shows us what, but for these other forces, a great mountain region would be like. It would be traversed from end to end by low and roughly parallel ridges, separated from one another by shallow valleys raised high aloft on the great plateau-pedestal. In the shallow valleys there would lie many lakes, some having no outlets, others drained by slow streams flowing along the strike of the ranges, and fed by driblets from the slopes of the flanking hills.

But at the ends and around the periphery of the plateau generally a different condition of things will be found. Let us regard the ends first. The slow flowing rivers of the plateau as they reach its extremity will become swift, where they plunge down to the plain. In proportion to their swiftness is the speed with which they cut down their beds into the mass of the plateau-pedestal. If the end of the plateau were a cliff, the rivers would tumble over it in waterfalls, and these would cut their way back and thus dig out cañons in place of the shallow valleys of the original wrinkling. In any case a similar result will be arrived at, and the plateau will be more and more cut down into deep valleys with high ridges between. What were originally small wrinkles above the mean level of the plateau and slight depressions beneath it will be changed by denudation into high mountains and deep valleys, their scale being determined by the amount of general elevation of the plateau above the low-lying country. As the general elevating process goes on, so does the excavation. The deep valleys will be formed first at the edge of the plateau. They will work back into its heart in process of time. The original Tibetan plateau is now greatly reduced, and only the remaining middle part of it preserves any resemblance to its primary surface-form. As you go eastward or westward from that central portion you come into ever deepening valleys and ever relatively higher peaks, measured from the neighbouring valley floor.