the cycle of development of land relief, consisting of the sequence of the stages “youth,” “maturity,” and “old age.” The theory was formulated by the American geographer and geomorphologist W. M. Davis at the turn of the 20th century. In the youthful stage, under the influence of tectonic uplifts, there appears a mountain relief, which is dissected through erosion (the washing out of rocks by rivers) into deep, narrow valleys and sharp-peaked ridges. In the mature stage erosion and denudation (the wearing down of rocks) widen the valleys, level out valley floors, and smooth out and round out slopes and watersheds. In the old age stage denudation levels out the relief to a “near-plain” state (peneplain), which completes the cycle. New tectonic uplifts may lead to a renewal of erosion and the rejuvenation of the relief, thereby beginning a new geographic cycle. According to Davis, variations in climate and, more important, denudation determine whether a geographic cycle is “normal” (water-erosion), glacial, arid (desert), or marine. This theory played a large positive role in the development of geomorphology, but it also contains a number of shortcomings. Tectonic uplifts are viewed merely as an initial impetus causing intensified denudation, which then proceeds independently of movements of the earth’s crust. Furthermore individual factors of denuda’tion are portrayed in isolation from each other and are identified as autonomous, parallel factors. The development of relief is viewed as a series of closed cycles, at the end of each of which the relief reverts to its initial state. The theory of the geographic cycle fails to provide the idea of a definite orientation in the evolution of the earth’s relief.
REFERENCESMarkov, K. K. Osnovnye problemy geomorfologii. Moscow, 1948.
Davis, W. M. Die erklärende Beschreibung der Landformen. Leipzig-Berlin, 1912.
Davis, W. M. Geomorfologicheskie ocherki. Edited by S. Iu. Geller, Iu. A. Meshcheriakov, and O. K. Parchevskii. Moscow, 1962. (Translated from English.)