Geomorphic Cycle

Context and Objectives

The geomorphic cycle was launched into the scientific world at a time when Charles Darwin's work was an overt and pervasive influence. The “cycle” is largely biological in tenor. However, Darwin's concept of evolution, dominated as it is by the concept of randomness, was modified by Davis into a concept of inevitable change over time, that is, mathematical probability became deterministic. This was also the period when eustatic theory, isostasy, and epeirogeny were all in their introductory phases within geomorphology. Davis did not accept all these new ideas but clearly embraced some of them.

Davis's objective was to develop and present a model of landscape development that was deductive and theoretical. Just how deductive Davis's formulation of the model really was has been widely debated. Davis wanted his model to be not only theoretical but also genetic, so the model was designed both to describe and to explain landforms. He did not attempt to describe the fundamental geologic origin of landscape but rather the subsequent geomorphic development. For example, he was not particularly interested in the initial uplift of a plateau or mountain system; rather, he sought to explain its development subsequent to uplift.

Essential Components

Initially, Davis forwarded five controlling factors for landscape development: (1) structure, [Page 1242](2) process, (3) stage, (4) relief, and (5) texture of dissection, and he also initially invoked the rate of uplift as important. However, he pruned his model vigorously, and structure, process, and stage are the three variables with which it is most widely associated. Even they are not coequal as stage was Davis's preeminent preoccupation. Stage is a relative, not absolute, temporal concept, being the amount of time elapsed since uplift. Consequently, a landscape may exhibit different stages in different parts.

The Davisian concept of stage was widely discussed in anthropogenic terms of youth, maturity, and old age. Youth follows uplift immediately and is a period when the relative relief of the landscape (i.e., the local difference between the valley bottom and the abutting mountain or ridge tops) increases. Youth ends when all the original landscape surface has been removed by erosion; specifically, this implies that valley sides have eroded so greatly as to have removed the original summits. During maturity, the landscape attains maximum relative relief, and valleys are V-shaped. As maturity advances, the landscape becomes more rounded and the valley system more extensive and better integrated, while floodplains emerge and expand. During old age, relative relief is greatly reduced. The surface becomes gently rolling with broad valleys with floodplains, ultimately producing a plain without relief. However, Davis chose to highlight the stage immediately prior to the ultimate landscape, thus the world famous “peneplain,” which should reflect little or none of its geologic structure and bear infrequent resistant elements standing up as “monadnocks” (these are hills or mountains descriptively, but their origin is specifically derived from a Davisian view of landscape development).

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