Aerial Photographs and Structural Geomorphology

Abstract

The intensive use of vertical aerial photographs to aid geological exploration during the last two decades has revealed serious weakness in some of the traditional concepts of American geomorphology. A new realization is now widely held, not by geomorphologists but by "photogeologists," namely, that tectonic elements of the crust (such as dipping strata, faults, joints, fold axes, flexures) can be found with aerial photographs in almost every square mile of the continental surfaces through their geomorphic expression. This has long been known of the deformed "mountain regions"; it is nearly as true of the so-called "plains" and "plateaus," even where tectonic elements are deeply buried by relatively undeformed, homoclinal strata. The writer attempts to present a usable revision of geomorphic concepts mainly through two basic principles: (1) the concept of essentially universal superposition of drainage in "flatland" regions, as well as in most tectonic systems, and (2) the concept of an almost universal tectonic influence on most continental drainage. Exceptions to the control of principles 1 and 2 are some, but not all, of the streams on deltas, volcanoes, lava flows, dune plains, and elsewhere. Elevated dissected bedrock benches of erosional origin are employed in explaining the usual process of stream adjustment to tectonic anomalies. The Pawhuska peneplain of central and southwestern central United States is briefly described. A distinction is made between tectonically influenced and tectonically adjusted drainage.