Dynamic equilibrium and landscape evolution

Abstract

The principle of dymamic equilibrium whenused to explain landscape freatures is not in itself an evolutionary model such as the geographic cycle. However, the tendency toward dynamic equilibrium is a universal principle that can be used to explain specific landscape features and problems, when it is assumed that the landscape has developed during a long period of continuous downwasting. This concep can be tested and compared with the multiple erosion cycle concept by examining a variety of specific freatures in a landscape, as the writer has done previously in the Shenandoah Valley of Virginia. Evolutionary models can be conceived assuming (1) a stable base level, (2) a rise in base level, or (3) a fall in base level. In the first model, a gradual lowering of relief would be expected, greater effects occurring near base level than farther away, somewhat like a single cycle in the Davisian model. If base level rises, there would be a drowning of the lower valleys but very little effect upstream, and the topography would continue to lower. If base level falls, erosion would be accelerated near the new base level, and the acceleration would affect an increasingly large area. New adjustments of slope to rock resistance would be made simultaneously. As has happened in the past, however, the model we adopt to explain landscapes must be related to prevailing thought in other fields of earth science.