Hours of Exercise in the Alps

by John Tyndall

But even after the snow has been squeezed to hard ice in the upper glacier region, it always contains a large amount of the air originally entrapped in the snow. The air is distributed through the solid in the form of bubbles, which give the ice a milky appearance. At the lower extremity of a glacier the ice, as everybody knows, is blue and transparent. The transition from one state to the other is not, in all cases, a gradual change which takes place uniformly throughout the entire mass. The white ice, on the contrary, of the middle glacier region is usually striped by veins of a more transparent character, the air which gives to the ice its whiteness having been, by some means or other, wholly or partially ejected from the veins. These veins sometimes give the ice of many glaciers a beautiful laminated appearance; vast portions, indeed, of various glaciers consist of this laminated ice.

The theory of the veins which perhaps first presents itself to the mind, and which is still entertained by many intelligent Alpine explorers, is that the veining of the middle glaciers is simply a continuation of the bedding of the névé; that not only do the annual snow-falls produce beds of great thickness, but every successive fall tends to produce a layer of less thickness, which layers, or the surfaces separating them, ultimately appear as the blue veins. This theory demands respectful consideration: on the exposed sections of the névé the lines of stratification are very manifest, exhibiting in many cases appearances strongly resembling that of the veined structure. Indeed, it was with a view to examine this subject more closely that I withheld my observations on the structure of the Mer de Glace in 1857, and betook myself once more to the mountains during the summer of 1858. My desire at that time was to settle once for all the rival claims of the only two theories which then deserved serious attention—namely, those of pressure and of stratification.

In pursuance of this idea, I first visited the Lower glacier of Grindelwald, one of the most accessible, and at the same time most instructive, in the entire range of the Alps. Ascending the branch of this glacier which descends from the Schreckhorn, the Strahleck, and the Finsteraarhorn, I came to the base of an ice-fall which forbade further advance. Quitting the glacier here, I ascended the side of the flanking mountain, so as to reach a point from which the fall, and the glacier below it, are distinctly visible; and from this position I observed the gradual development and perfecting of the structure at the base of the fall. On the middle of the fall itself no trace of the structure was manifest; but where the glacier changed its inclination at the bottom, being bent upwards so as throw its surface into a state of intense longitudinal compression, the blue veins first made their appearance. The base of the fall was a true structure mill, where the transverse veins were manufactured, being afterwards sent forward, giving a character to portions of the glacier which had no share in their formation.

I afterwards examined the fall from the opposite side of the valley, and corroborated the observations. It is difficult, in words, to convey the force of the evidence which this glacier presents to the observer who sees it; it seems in fact like a grand laboratory experiment made by Nature herself with especial reference to the point in question. The squeezing of the mass, its yielding to the force brought to bear upon it, its wrinkling and scaling off, and the appearance of the veins at the exact point where the pressure begins to manifest itself, leave no doubt on the mind that pressure and structure stand to each other in the relation of cause and effect, and that the stratification could have nothing to do with the phenomenon.

I subsequently crossed the Strahleck, descended the glaciers of the Aar, crossed the Grimsel, and examined the glacier of the Rhone. This glacier has also its grand ice-fall. In company with Prof. Ramsay, I climbed in 1858 the precipices flanking the fall at the Grimsel side. What has been stated regarding the Grindelwald ice-fall is true of that of the Rhone; the base of the cascade is the manufactory of the structure; and, as all the ice has to pass through this mill, the entire mass of the glacier from the base of the fall downwards is beautifully laminated.

Descending the valley of the Rhone to Viesch, I went thence to the Æggischhorn, and remained for eight days in the vicinity of the Great Aletsch glacier—the noblest ice-stream of the Alps. A highly intelligent explorer had adduced certain phenomena of this glacier as an evidence against the pressure theory of the veined structure; and I did not think myself justified in quitting the place until I had perfectly satisfied myself that the Aletsch not only presented no phenomena at variance with the pressure theory, but exhibited some which seemed fatal to the theory of the stratification.

I subsequently proceeded to Zermatt, and spent ten days on the Riffelberg, exploring the entire system of glaciers between Monte Rosa and the Mont Cervin. These glaciers exhibit, perhaps in a more striking manner than any others in the Alps, the yielding of glacier ice when subjected to intense pressure. The great western glacier of Monte Rosa, the Schwartze glacier, the Trifti glacier, and the glaciers of St. Theodule, are first spread out as wide and extensive névés over the breasts of the mountains. They move down, and are finally forced into the valley containing the trunk, or Görner glacier. Here they are squeezed to narrow strips, which gradually dwindle in width until they form driblets not more than a few yards across. From the Görner Grat, or from the summit of the Riffelhorn, these parallel strips of glacier, each separated from its neighbour by a medial moraine, present a most striking and instructive appearance.

The structure of these glaciers was carefully examined, and in all cases as I travelled from regions where the pressure was feeble to others where it was intense, the ice changed from a state almost, if not entirely, structureless, to one in which the veining was exhibited in great perfection. Each glacier, for example, where it met the opposing mass in the trunk valley, and was pressed against the latter by the thrust from behind, exhibited a beautifully developed structure.

Proofs have been already adduced that the Glacier du Géant is in a state of longitudinal compression; it has also been shown that the seams of white ice which intersect this glacier are due to the filling up of the channels of glacier streams by snow, and the subsequent compression of the substance. Here, then, we have a vast ice-press which furnishes us with a test of the pressure theory. Both in 1857 and 1858 I found many of these seams of white ice intersected by blue veins of the finest and most distinct character, their general direction being at right angles to the direction of pressure.