. The Andes of southern Peru; geographical reconnaissance along the seventy-third meridian. Yale Peruvian Expedition (1911); Physical geography; Geology. 296 THE ANDES OF SOUTHERN PERU. schrunds, how shall we explain the topographic depressions ex- cavated underneath the snow? If cirque formation can be shown to take place without concentrated frost action at the foot of the bergschrund, then is the bergschrund not a secondary rather than a primary factor? And must we not further conclude that when present it but hastens an action which is common to all snow-cov- ered recesses? It is a pleasur
. The Andes of southern Peru; geographical reconnaissance along the seventy-third meridian. Yale Peruvian Expedition (1911); Physical geography; Geology. 296 THE ANDES OF SOUTHERN PERU. schrunds, how shall we explain the topographic depressions ex- cavated underneath the snow? If cirque formation can be shown to take place without concentrated frost action at the foot of the bergschrund, then is the bergschrund not a secondary rather than a primary factor? And must we not further conclude that when present it but hastens an action which is common to all snow-cov- ered recesses? It is a pleasure to say that we may soon have a restatement of the cirque problem from the father of the bergschrund idea. The argument in this chapter was presented orally to him after he had remarked that he was glad to know that some one was finding fault with his hypothesis. "For," he said, with admirable spirit, " I am about to make a most violent attack upon the so-called Johnson ; I wish to say frankly that while he regards the following argument as a valid addition to the problem, he does not think that it solves the problem. There are many of us who will read his new explanation with the deepest interest. We shall begin with the familiar fact that many valleys, now without perpetual snow, formerly contained glaciers from 500 to 1,000 feet thick and that their snowfields were of wide extent and great depth. At the head of a given valley where the snow is crowded into a small cross-section it is compacted and suffers a re- duction in its volume. At first nine times the volume of ice, the gradually compacting neve approaches the volume of ice as a limit. At the foot of the cirque wall we may fairly assume in the absence of direct observations, a. volume reduction of one-half due to com- pacting. But this is offset in the case of a well-developed cirque by volume increases due to the convergence of the snow from the surrounding slopes, as shown in Fig. 196.
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