Mmm ^Lur CENTENNIAL ARTICLE

mmm ^lUr CENTENNIAL ARTICLE Landscape analysis and the search for geomorphic unity DALE F. RITTER Department of Geology, Southern Illinois University, Carbondale, Illinois 62901 ABSTRACT INTRODUCTION Davis' generalized statement; it is, in fact, true and certainly eloquent in its simplicity. It does, Geomorphology has been an integral part The accumulation of knowledge in any however, give geomorphologists the option to of geological science since the inception of the science inevitably results in the fragmentation of emphasize one variable to the exclusion of the Geological Society of America, even though that science into distinct subparts. The Geologi- others, thereby leading to the problem of diverse different investigative goals have existed con- cal Society of America, for example, presently approach and purpose. Such difficulties are es- tinuously in the discipline. The dichotomy of recognizes ten divisions which derive identity pecially apparent when either time or process purpose began with the vastly different per- because their members share mutual scientific becomes the primary target of study because each ception of landscape analysis embraced by interests. Underlying this commonality are intel- has a different goal and each requires a different William Morris Davis and G. K. Gilbert. His- lectual threads which, woven together, provide scientific approach. Therefore, the very nature of torical and physical geomorphic studies have the philosophic basis for each subdiscipline and landscapes requires geomorphology to assume always been conducted simultaneously, but manifest the scientific goals that make a particu- the dual nature of being both a historical and one of these research activities has dominated lar field unique. It is also true, however, that physical science. the field at any given time. During the first recognition of common goals does not insure When geomorphology is adopted as a histori- half of this century, most geomorphic work agreement about how to achieve those goals or cal science, landscapes (and their component was devoted to the interpretation of long- what investigative thrust should be first among landforms) are used to discern the sequence of term, evolutionary history of regional land- all others. Nonetheless, in most disciplines, the geological events that are reflected and pre- scapes. In the past four decades, however, intellectual bonds are stronger than differences served in their present condition. In this ap- research has concentrated on the study of which arise concerning goals or methodology. proach, erosional and depositional landforms geomorphic processes. This revised direction The Geological Society of America is the only are used as evidence for tectonic or climatic placed greater emphasis on the physical com- organization that recognizes geomorphology as events, and the time and sequence of those ponent of geomorphology and provided a an integral part of geology and correctly joins it events are the research goals. When geomor- more complete understanding of the time fac- with Quaternary Geology as a major Society phology is considered to be a physical science, tor in landscape analysis. Historical geomor- division. Geomorphology is the scientific study research analysis revolves around process and is phology is now less concerned with theories of landforms, and because landforms constitute totally different. This approach attempts to ex- of cyclic-time landscape development and the building blocks of regional landscapes, the plain why rather than when landforms develop. more involved in determining the time and science has historically been associated with the Process geomorphologists observe physical sequence of shorter episodes of geomorphic development of landscapes. The question, of phenomena over short time spans, with the ul- disequilibrium caused by tectonism and/or course, is how does one analyze a landscape? timate goal being prediction of what will occur climate change. William Morris Davis provided the answer by if factors controlling process (climate, tectonics, The tenor of future research in surficial stressing that landforms (and therefore land- human activity) are altered. Thus, the study of geology will require input from both physical scapes) are a function of the combined effect of process often concentrates on the mechanics of and historical geomorphology, and therefore structure, process, and time, where structure re- agents producing erosion or deposition rather a greater unity of purpose among geomor- fers to all aspects of geology (lithology, stratig- than the landforms which they create. phologists can be expected. Geomorphol- raphy, tectonic characteristics) and time refers to The dichotomy of approach in geomorphologists will have the opportunity to provide a relative stage of development rather than abso- ogy is not new. It developed in North America geologists and engineers with useful data lute years. Thus, in simple terms, the form or at the same time that seminal observations were about major scientific and technical problems forms of a landscape reflect some unique ac- leading to the creation of geomorphology as a related to plate-tectonic theory, interpreta- commodation between a particular geologic distinct science. Such multiplicity of purpose is tion of the stratigraphic record, and predic- framework being acted on by both endogenic not necessarily bad, especially when it leads to tion of landform stability for environmental and exogenic processes over an indistinct period cutting-edge discoveries. It can be argued, how- planning. of time. There is nothing inherently wrong with ever, that diversity of goal and approach, and Geological Society of America, v. 100, p. 160-171, 3 figs., 3 tables, February 1988. 160 Downloaded from https://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/100/2/160/3379715/i0016-7606-100-2-160.pdf by Utah State University Libraries user on 24 August 2020 LANDSCAPE ANALYSIS AND THE SEARCH FOR UNITY 161 the vagueness of paradigms, have given geo- would require greater erosional and transporta- Gilbert's work on Lake Bonneville (Gilbert, morphology the undeserved reputation of hav- tional energy, which Gilbert believed would be 1890) demonstrated that he considered geomor- ing less scientific rigor than other segments of provided by a change in declivity (channel phic history as nothing more than episodes of geoscience. Geomorphologists know that this is slope). This, of course, was the first expression of equilibrium being periodically disrupted by geo- not true, but many in other branches of geology grade in geomorphic analysis and represents the logic events (Baker and Pyne, 1978). Even hold lingering doubts and are confused as to quintescence of Gilbert's equilibrium approach though he suggests that one goal of the Bonne- what it is that geomorphologists actually do. in all aspects of his varied geological work. ville study was local Pleistocene history, his This paper is an attempt to trace how the Gilbert's preoccupation with equilibrium also main emphasis was placed on shoreline proc- primary emphasis in geomorphic thinking has filtered into his thinking about the relationship esses. After he understood what features resulted changed since the inception of the Geological between process and landform; in fact, he postu- from those processes, the landforms (for exam- Society of America and, wherever possible, lated physical "laws" to explain topography. His ple, bars, strandlines) were used to reconstruct stress how the Society has functioned as a vehi- laws of structure (geology), divides, and declivi- the positions of various lake levels. Thus, his cle for that change. It has not been written for ties stemmed from his belief that the interaction "geological history" relied totally on the study of geomorphologists; they know what they do and of each determined the landscape character. physical processes and certainly did not consist why they do it. Instead, the paper is directed Terms such as "dynamic adjustment" and of the multidisciplinary approaches used by toward other geoscientists who may perpetuate "balanced condition" permeate his writing and modern Quaternary geologists. Furthermore, his misconceptions concerning geomorphology be- illustrate his perception that landforms reflect precise leveling of shoreline features led him to cause they cling to ideas which lend themselves some unique balance between process and important insights about crustal rebound asso- to easy pedagogy but are possibly wrong and geology. For example, he stated (Gilbert, 1877, ciated with the removal of stress as Lake Bonne- certainly do not reflect geomorphic science as it p. 115-116): ville disappeared. Gilbert, therefore, considered is today or what it will be like in the future. landform history primarily because it preserved the record of both endogenic and exogenic proc- APPROACHES OF LANDSCAPE Erosion is most rapid where the resistance is least; and esses. He had little interest in determing when, hence as the soft rocks are worn away the hard are left or in what sequence, events occurred, and thus ANALYSIS prominent. The differentiation continues until an equilibrium is reached through the law of declivities. his work often strayed from our usual under- The Geomorphology of G. K. Gilbert When the ratio of erosive action as dependent on standing of historical geology. declivities becomes equal to the ratio of resistances as In 1905, Gilbert was given the task of assess- dependent on rock character, there

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