Features of Alpine Scenery Due to Glacial Protection Author(S): E
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Features of Alpine Scenery Due to Glacial Protection Author(s): E. J. Garwood Source: The Geographical Journal, Vol. 36, No. 3 (Sep., 1910), pp. 310-336 Published by: geographicalj Stable URL: http://www.jstor.org/stable/1777308 Accessed: 20-06-2016 10:24 UTC REFERENCES Linked references are available on JSTOR for this article: http://www.jstor.org/stable/1777308?seq=1&cid=pdf-reference#references_tab_contents You may need to log in to JSTOR to access the linked references. Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at http://about.jstor.org/terms JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Wiley, The Royal Geographical Society (with the Institute of British Geographers) are collaborating with JSTOR to digitize, preserve and extend access to The Geographical Journal This content downloaded from 131.172.36.29 on Mon, 20 Jun 2016 10:24:19 UTC All use subject to http://about.jstor.org/terms 310 FEATURES OF ALPINE SCENERY DUE TO GLACIAL PROTECTION. expedition loaded itself with scientific treasures, which, no doubt, will throw new light on Central Asia in former times beyond what the archaological section of the Asiatic Museum of the Imperial Academy of Sciences affords. FEATURES OF ALPINE SCENERY DUE TO GLACIAL PROTECTION.* By Professor E. J. GARWOOD, M.A., Sec. G.S. 1. Introduction. 5. Hanging Valleys. 2. The Plateau. 6. Valley Steps. 3. Aretes. 7. The Steep South Side of the Alps. 4. Cirques. 8. Conclusion. 1. INTRODUCTION. WHEN we review the progress that has been made in the study of Physical Geography, or, more strictly, Geomorphology, during the last few years, we find nothing more striking than the revived interest in the features characteristic of glaciated districts. Thus the Alps, Himalayas, Scandinavia, Alaska, and New Zealand have in turn received attention. On the whole, there appears to be a strong consensus of opinion that glacial action has been a much more potent agent in the production of Alpine scenery than was formerly imagined. The monumental work of Penck and Bruckner on the Alps in the glacial period,~ founded as it is on care- fully observed facts, must long remain a classic work on this fascinating region; while Prof. W. M. Davis, in America, has applied the deductive method with the scholarly thoroughness which distinguishes all his writings. These authors, together with Hess, Tarr, and others, have all been led to assign to ice-erosion a very important part in the formation of the features peculiar to Alpine scenery. Their views may be summed up in the words of Prof. Davis: " The rate of glacial erosion, in whatever way it may be accomplished, need not be very rapid, the only requirement in this respect being . that it shall be significantly more rapid than normal erosion." + This is really the crux of the matter. Does an ice-cap lying on a plateau carve the surface more rapidly than the normal weathering agents ? Do snow and ice lying on ledges, or resting in gullies, degrade more rapidlythan do frost or water f. and does a glacier overdeepen its bed more rapidly than would a river flowing in the same valley 2 The difference of opinion in this respect dates from some years back; as long ago as 1888 Mr. Douglas Freshfield published a paper in this Society's Proceedings on " The Conservative Action of Ice," while Prof. Bonney has more than once expressed very similar views. No one with any knowledge of glaciated regions doubts that moving * Royal Geographical Society, June 20, 1910. t ' Die Alpen im Eiszeitalter.' Leipzig: 1909. t W. M. Davis, Q.J.G.S., vol. 65, p. 313. This content downloaded from 131.172.36.29 on Mon, 20 Jun 2016 10:24:19 UTC All use subject to http://about.jstor.org/terms FEATURES OF ALPINE SCENERY DUE TO GLACIAL PROTECTION. 311 ice erodes; that is not now the question.* The whole problem turns on the relative rate of erosion accomplished by ice as compared with that which would take place over the same district by ordinary erosive agents, namely, weathering, wind, frost, rain, and running water, more especially in a district which is partially covered and partially free from ice. It may eventually be proved beyond doubt that ice is the greater erosive agent, but this has not been done. It may also be shown conclusively that all the features to be presently described can be satisfactorily accounted for by ice erosion; but so far this is not the case. It is intended in the present communication to consider more fully than has yet been done, what characteristic Alpine features might be developed on the assumption that ice, on the whole, erodes less rapidly than other denuding agents, and that, under certain conditions, it may act relatively as a protective agent. 2. THE PLATEAU. Let us consider, in the first place, a tableland on which snow accumu- lates during a glacial period. This snow gradually compacted into ice will cover the plateau and protect it from all the ordinary weathering agents of a temperate climate, including the action of frost, just as effectually as if it were covered by a deposit of impervious clay. Any erosion, then, that the ground beneath sustains must be due to the action of the ice itself. Erosion from this cause must be very slight indeed, as the motion will resemble the creep of a sheet of lead covering a counter, and the chief movement will take place in the upper layers. It seems practically certain, then, that an ice-covered surface which is on the whole horizontal will be relatively protected, and that the tablelands and plateaux in a glaciated district will have their pre-glacial features to a great extent preserved; the sharp edges of a plateau, however, where snow cannot lie continuously, but must melt and slide in summer, will not be protected in the same way, but will be subjected to other denuding agents. This fact was vividly brought home to the writer during two visits to Spits- bergen. Here plateau protection reaches its most marked development, while the plateau edges show some of the most remarkable examples of symmetrical river drainage to be found in the world. This is due to the present climatic conditions; the snow accumulated on the plateau during the long winter night melts continuously during the summer day, thus supplying abundant water, which, pouring over the plateau edge, sculptures the flanks into the almost ideal drainage system shown in Plate I. Fig. 1. Similar features on a smaller scale are constantly found in the Alps: a good example is the old Badile plateau, near the head of the Bondasca valley, shown in Plate I. Fig. 2, where the stream has cut back its head- waters into the old plateau step by step as the ice melted back and ceased to afford protection. * Garwood, "Hanging Valleys in the Alps and Himalayas," Q.J.G.S., vol. 58, 1902. This content downloaded from 131.172.36.29 on Mon, 20 Jun 2016 10:24:19 UTC All use subject to http://about.jstor.org/terms 312 FEATURES OF ALPINE SCENERY DUE TO GLACIAL PROTECTION. 3. AReTES. The symmetrical ridges known as aretes, found in so many mountain districts, are essentially characteristic of glaciated countries. Their notable feature is the wonderfully even grade of their crests, cutting the sky-line in a distant view as though (as noted by Ruskin) drawn with a ruler, or slightly concave, resembling the most perfect denudation curve (P1. II. Fig. 1). Many of these aretes, however, on a nearer view, show the presence of sharp projecting towers of rock, the " gendarmes " so well known to mountaineers, which figure so prominently in accounts of Alpine ascents. The arete, indeed, is the route most usually followed during ascents of the higher peaks, as it forms generally, not only the safest, but often the quickest and least tedious route to the summit, on account of the even slope of its crest. It is curious that this even character, which, as stated above, is essentially a feature of glaciated regions, has not received more attention. It cannot have been produced by water-erosion, and cannot be considered a feature retained from pre- glacial times; neither would the disintegrating action of frost alone account for its symmetrical character. It appears to be essentially a case where ice protection may be legitimately invoked. At the beginning of a glacial period snow would gradually accumulate above the snow- line in the uneven hollows of the pre-glacial ridge, where it would become gradually compacted into ice and remain. In the mean time the steep projecting portions would be subject to the action of frost, by which they would be gradually converted into gendarmes, and finally reduced to the level of the surface of the ice in the hollows. After this the ice and the rock bounding it would be reduced at an equal rate, until finally there would be no hollows left in which snow could accumulate, and the arete would be reduced to an even grade. If wide enough, this might be uniformly covered with snow, as in the case of portions of the Bernina and Roseg aretes (P1. II. Fig. 2). It is obvious that this condition is only approximately produced; the even grade in other cases is partly due to the infilling of the depressions by ice, thus raising the surface to an average level.