Strahler, Arthur Newell
STRAHLER, ARTHUR NEWELL
geology, physical geography, quantitative-dynamic approach to geomorphology, slopes, drainage basins.
In the middle of the twentieth century, Strahler spearheaded the campaign to fundamentally change how geologists and physical geographers pursue the study of landforms, which is called geomorphology. He challenged geomorphologists to move away from the traditional qualitative and descriptive Davisian approach to landform studies (named for William Morris Davis) that had been developed in the late nineteenth century and which emphasizes the long-term evolution of landscapes. In its place, Strahler advocated a quantitative, dynamic, process-oriented approach to the study of landforms that relies on detailed field observation, numerical measurements of form and process, mathematical representations, statistical methods, and systems analysis. Strahler’s conception of geomorphology was widely adopted in the second half of the twentieth century, and it remained the foundation of geomorphic research and education into the early 2000s.
Early Life and Education Strahler was born in Kolhapur, India, to parents who were Presbyterian missionaries. Back in the United States he went to school in the Chicago area before attending the College of Wooster in Ohio, where he met his future wife, Margaret (Marge) Strahler. At Wooster he majored in geology and became most interested in structural geology and geomorphology as taught by Charles B. Moke and Karl Ver Steeg, respectively. The study of landforms in the United States at that time was almost completely dominated by the qualitative, descriptive approach developed by the prominent Harvard University professor William Morris Davis. Davis’s deductive theory of landscape development, called the geographical cycle, considered landforms to be the result of geologic structure, landforming processes, and time, the latter of which was referred to as stage. The emphasis in Davisian geomorphology was on the stage factor, rather than structure or process. Davis’s most influential contribution was in positing how a landscape of given initial geological structure, such as an uplifted fault block, subjected to processes of weathering, erosion, transportation, and deposition in a humid climate, would evolve over long periods of time. Davis outlined qualitatively and with detailed drawings what a landscape would look like relatively soon after the initial structural relief came into existence (youthful stage of development), after a significant passage of time (mature stage of development), and long after the initial uplift (old age). In the Davisian approach to landform analysis, geomorphologists interpreted the landforms or landform assemblages in a region according to (1) their inferred stage of development; (2) whether it appeared that an erosional cycle had been interrupted (rejuvenation); and (3) if the features had been subjected to multiple erosion cycles. Against this traditional backdrop, as a college junior, Strahler attended summer geology field camp in Wisconsin under the then-controversial geomorphologist J Harlen Bretz. Mainstream geomorphologists and geologists at the time considered Bretz’s claim that field evidence in the Channeled Scabland region of the Pacific Northwest revealed the occurrence of a cataclysmic flood, which he called the Spokane Flood, to be outlandish. Much of Strahler’s own later field studies consisted of similar collections of detailed field evidence accompanied by interpretation in terms of landforming processes.
Graduate Education and Early Career After receiving his BA from the College of Wooster in 1938, Strahler moved to New York City to begin graduate study in the Department of Geology at Columbia University supported by a Britton scholarship and later a university fellowship. He soon decided to emphasize geomorphology in his graduate studies and was directed in his work by Professor Douglas Johnson.
For his master’s research, Strahler studied landslides along the Vermilion and Echo Cliffs in the Grand Canyon region of northern Arizona. He conducted this work completely within the Davisian paradigm of the geographical cycle, and his resulting paper includes an outline of the ideal cycle of erosion that Strahler inferred must account for the landslides. Nevertheless, because of his careful field observations on the correlation of the slope failures with the occurrence of weak shale rocks, that is, on elements of the geomorphic structure and process, Strahler concluded that Davis’s temporal explanation of the features as the result of two erosion cycles was incorrect.
Strahler conducted considerable additional fieldwork throughout the Grand Canyon region, in part as field assistant to a fellow graduate student. In a series of resulting publications in the 1940s, Strahler continued to use fundamental field observations to challenge the Davisian two-erosion cycle interpretation of the recent geologic history of the Grand Canyon region. Although Strahler never explicitly stated so, the implication was that if the Davisian explanations are not correct for a region as important as the Grand Canyon area, they might be incorrect in other regions as well. In a separate 1946 publication, “Geomorphic Terminology and Classification of Land Masses,” Strahler also criticized Davis’s use of some specific landform terms (e.g., mountains, plains, plateaus) as being inconsistent. Despite these criticisms of some of the work of Davis and Davisian geomorphologists, in his publications Strahler continued to use the basic life-cycle terminology of youth, maturity, and old age, and to make his criticisms from within the Davisian paradigm.
For his dissertation research, Strahler tackled another large, important field area, the Appalachian Mountains. Strahler focused his efforts in Pennsylvania, testing multiple hypotheses that had been postulated previously by Davisian geomorphologists to explain the development of the present drainage system there. Once again, Strahler used extensive primary field observations, detailed map interpretation, a thorough review of the literature, and his knowledge of stream processes to assess the various explanations. Although he was already drifting from the established approach by focusing on detailed, site-specific field evidence and stream processes, his conclusions remained couched within the Davisian paradigm of landscape evolution. Strahler relied even more on the crucial role of force and resistance, that is, geomorphic processes, in explaining the unusual form of meanders in a Pennsylvania river in a subsequent, related paper.
Strahler had been appointed to the Columbia University faculty as a lecturer in 1941 while still a graduate student. Despite the demands of being a lecturer while also a graduate student, his publication record of the 1940s shows tremendous enthusiasm for tackling large-scale problems as well as great respect for previous researchers. That record, however, reveals an even greater respect for the field evidence and for invoking the best explanation for that evidence, even if it disagrees with explanations of eminent predecessors.
Professional Maturity: The 1950s Strahler had been deeply impressed by the quantitative approach to drainage-system analysis detailed in a 1945 paper that was published in the Geological Society of America Bulletin by the civil engineer Robert Elmer Horton. Recognizing, in contrast to Horton’s contributions, the severe limitations of working solely within the qualitative confines of the Davisian geographical cycle, Strahler began the decade of the 1950s by unleashing a blunt, but effective, criticism of Davis’s stage approach to geomorphology while advocating what he termed the dynamic-quantitative system of landform analysis. In what was one of the most influential papers in twentieth-century geomorphology, Strahler (1950a) used the opportunity of writing a paper for an issue of the Annals of the Association of American Geographers published in honor of the anniversary of Davis’s birth to characterize the scientific value of Davis’s qualitative, descriptive approach to geomorphology as inadequate and superficial. He argued that a meaningful understanding of landforms instead requires quantitative measurements and numerical analyses of processes and forms, as well as the general application to landform studies of methods and techniques used in the other sciences. Only in this way, according to Strahler, would geomorphologists be able to solve real-world problems in which landforms and landforming processes were involved. Strahler also advocated employing the concepts of open systems and steady state, as used in thermodynamics and biological science, to bring geomorphology into line with current advances in other sciences. Strahler warned, moreover, that if geomorphologists failed to make this methodological shift, they risked forfeiting their field of study to engineers and hydrologists. With a separate paper, Strahler (1950b) provided a detailed example of how to apply the quantitative-dynamic approach to studying slopes using statistical methods. Strahler’s fullest statement of what modern geomorphology should encompass was published in 1952 as “Dynamic Basis of Geomorphology.” In that paper Strahler outlined in detail how geomorphic processes are essentially chemistry and physics applied to the variety of earth materials.
Strahler’s view of the direction in which the field should move resonated with the new generation of geomorphologists in the postwar era, and the movement grew to dominate geomorphology in the second half of the twentieth century. His logical and straightforward arguments for and examples of the quantitative-dynamic approach to geomorphology changed the direction of the discipline in the mid-twentieth century and enabled its practitioners to communicate more effectively with scientists in other disciplines.
Throughout the 1950s, Strahler published a steady stream of methodological papers: (1) encouraging geomorphologists in geology and geography to use various quantitative and statistical methods; and (2) demonstrating how these methods could be applied in analyzing geomorphic systems. He repeatedly credited Horton for his early application of such techniques to stream and drainage basin analysis. Among other things, Horton had advanced the fundamental concept of stream ordering, that is, of quantitatively describing where a given stream segment lies in the hierarchy of a drainage basin’s tributaries. Strahler found it useful to modify Horton’s stream ordering technique slightly to enhance the ease with which stream orders are subjected to further numerical assessment. In Strahler’s version, streams without tributaries are first-order channels, two first-order channels must meet to form a second-order channel, two second-order channels join to create a third-order channel, and so forth. Strahler’s version of stream ordering remains an important, fundamental element in the study of streams and drainage systems.
The professional journal articles that Strahler published in the 1950s contain a strong instructional aspect. They inform readers about the quantitative-dynamic approach to geomorphology and on various ways to implement it. The instructional aspect of these papers reflects one of Strahler’s most significant professional attributes—his ability to educate others.
The Educator Strahler’s influence reached far beyond the mid-twentieth-century geomorphologists who read his published articles. Strahler enthusiastically involved his graduate students at Columbia in the paradigm shift to the process approach to geomorphology. Several of his graduate students went on to become among the most successful practitioners of process geomorphology in the second half of the twentieth century. Students with whom he worked at Columbia University included Richard Chorley, Donald Coates, Mark Melton, Marie Morisawa, Stanley Schumm, and Michael Woldenberg. Although Strahler was a faculty member of the Columbia University Geology Department, achieving the rank of professor in 1958 and serving as department chair from 1959 to 1962, he also served the university by representing physical geography on the committee overseeing instruction and advanced degrees in geography. Because in the United States geomorphology is a subfield of both geology and physical geography, Strahler’s role in championing the paradigm change from Davisian to process geomorphology is equally well known in both disciplines.
Beyond the subfield of geomorphology, Strahler is a well-known name to geologists and physical geographers of all specialties in part because of the extensive list of thorough, well-organized, and well-illustrated textbooks that he authored and coauthored, especially in physical geography but also in physical geology and other aspects of the earth and environmental geosciences. Beginning with publication of his first physical geography textbook in 1951, Strahler authored at least eighteen different textbooks, many through multiple editions. In 1966, he published the popular book A Geologist’s View of Cape Cod for the lay reader. His powerful incorporation of systems concepts into physical geography textbooks set the standard for the rest of the century and continued to be emulated into the early 2000s.
Strahler’s research, productivity, and influence did not end when he retired from formal university teaching. He moved in 1973 to Santa Barbara, where he continued to work on his existing book projects and develop new ones, some of which he coauthored with his son, the geographer Alan H. Strahler. Strahler’s enduring importance to the field of physical geography is illustrated by the fact that the first paper published in the journal Physical Geography is a contribution by Strahler (1980) on systems theory. During this period he also wrote an informative retrospective article on his days at Columbia University and authored books on the evolution-creationism controversy, the philosophy of science, and plate tectonics.
Strahler died in New York on 6 December 2002, survived by his son Alan, daughter Elaine, and their respective families. During his long, influential, and productive career, Strahler had been affiliated with the Geological Society of America, the Association of American Geographers, the American Geographical Society, the American Association for the Advancement of Science, the American Geophysical Union, the American Meteorological Society, the National Association of Geology Teachers, Sigma Xi, and Phi Beta Kappa. He received a distinguished service award from the Geographic Society of Chicago and had conducted important contract research for the U.S. Office of Naval Research. Among his most enduring contributions to the science of geomorphology is his redirection of the discipline away from Davisian geomorphology and toward the measurement, numerical assessment, and systematic analysis of landforms and landforming processes.
WORKS BY STRAHLER
“Landslides of the Vermilion and Echo Cliffs, Northern Arizona.” Journal of Geomorphology 3 (1940): 285–301.
“Geomorphic Significance of Valleys and Parks of the Kaibab and Coconino Plateaus, Arizona.” Science 100 (8 September 1944): 219–220.
“Valleys and Parks of the Kaibab and Coconino Plateaus, Arizona.” Journal of Geology 52 (1944): 361–387.
With Donald L. Babenroth. “Geomorphology and Structure of the East Kaibab Monocline, Arizona and Utah.” Geological Society of America Bulletin 56 (1945): 107–150.
“Hypotheses of Stream Development in the Folded Appalachians of Pennsylvania.” Geological Society of America Bulletin 56 (1945): 45–87.
“Elongate Intrenched Meanders of Conodoguinet Creek, PA.” American Journal of Science 244 (1946): 31–40.
“Geomorphic Terminology and Classification of Land Masses.” Journal of Geology 54 (1946): 32–42.
“Geomorphology and Structure of the West Kaibab Fault Zone and Kaibab Plateau, Arizona.” Geological Society of America Bulletin 59 (1948): 513–540.
“Davis’ Concepts of Slope Development Viewed in the Light of Recent Quantitative Investigations.” Annals of the Association of American Geographers 40 (1950a): 209–213.
“Equilibrium Theory of Erosional Slopes Approached by Frequency Distribution Analysis.” American Journal of Science248 (1950b): 673–696, 800–814.
“Dynamic Basis of Geomorphology.” Geological Society of America Bulletin 63 (1952): 923–938.
“Hypsometric (Area-Altitude) Analysis of Erosional Topography.” Geological Society of America Bulletin 63 (1952): 1117–1141.
“Statistical Analysis in Geomorphic Research.” Journal of Geology 62 (1954): 1–25.
“Quantitative Slope Analysis.” Geological Society of America Bulletin 67 (1956): 571–596.
“The Nature of Induced Erosion and Aggradation.” In Man’s Role in Changing the Face of the Earth, edited by William L. Thomas Jr., with the collaboration of Carl O. Sauer, Marston Bates, and Lewis Mumford. Chicago: University of Chicago Press, 1956.
“Quantitative Analysis of Watershed Geomorphology.” Transactions, American Geophysical Union 38 (1957): 913–920.
“Dimensional Analysis Applied to Fluvially Eroded Landforms.” Geological Society of America Bulletin 69 (1958): 279–299.
With E. Donaldson Koons. Objective and Quantitative Field Methods of Terrain Analysis. U.S. Office of Naval Research Final Report of Contract 266-50, 1960.
Final Report of Project NR 388-057. U.S. Office of Naval Research Final Report of Contract 266-68, 1964.
A Geologist’s View of Cape Cod. Garden City, NY: American Museum of Natural History [by] Natural History Press, 1966.
“Systems Theory in Physical Geography.” Physical Geography 1 (1980): 1–27.
Science and Earth History: The Evolution/Creation Controversy. Buffalo, NY: Prometheus, 1987.
“Quantitative/Dynamic Geomorphology at Columbia 1945–60: A Retrospective.” Progress in Physical Geography 16 (1992): 65–84.
Understanding Science: An Introduction to Concepts and Issues. Buffalo, NY: Prometheus, 1992.
Plate Tectonics. Cambridge, MA: Geo-Books, 1998.
Baker, Victor R. “The Spokane Flood Controversy and the Martian Outflow Channels.” Science 202 (1978): 1249–1256.
Bretz, J Harlen. “The Channeled Scablands of the Columbia Plateau.” Journal of Geology 31 (1923): 617–649.
Davis, William M. “The Rivers and Valleys of Pennsylvania.” National Geographic Magazine 1 (1889): 183–253.
———. “The Geographical Cycle.” Geographical Journal 14 (1899): 481–504.
———. “An Excursion to the Grand Canyon of the Colorado.” Harvard College Museum of Comparative Zoology Bulletin 38 (1901): 107–203.
Horton, Robert E. “Erosional Development of Streams and Their Drainage Basins: Hydrophysical Approach to Quantitative Morphology.” Geological Society of America Bulletin 56 (1945): 275–370.
Sack, Dorothy. “New Wine in Old Bottles: The Historiography of a Paradigm Change.” Geomorphology 5 (1992): 251–263.
Santa Barbara News-Press, Obituary of “Strahler, Arthur Newell,” 29 December 2002.
Schumm, Stanley A. “Arthur Newell Strahler (1918–2002).” Annals of the Association of American Geographers 94 (2004): 671–673.
Tinkler, Keith J. A Short History of Geomorphology. London: Croom Helm, 1985.