Ancient Geomorphology
The first theory of Geomorphology was perhaps devised by the Chinese scientist and statesman Shen Kuo (1031–1095 AD). This was based on his observation of marine fossil shells in a geological stratum of a mountain hundreds of miles from the Pacific Ocean. Noticing bivalve shells running in a horizontal span along the cut section of a cliffside, he theorized that the cliff was once the pre-historic location of a seashore that had shifted hundreds of miles over the centuries. He inferred that the land was reshaped and formed by soil erosion of the mountains and by deposition of silt, after observing strange natural erosions of the Taihang Mountains and the Yandang Mountain near Wenzhou.He promoted the theory of gradual climate change over centuries of time once ancient petrified bamboos were found to be preserved underground in the dry, northern climate zone of Yanzhou, which is now modern day Yan’an, Shaanxi province.
Early modern Geomorphology
The term Geomorphology seems to have been first used by Laumann in an 1858 work written in German. Keith Tinkler has suggested that the word came into general use in English, German and French after John Wesley Powell and W. J. McGee used it during the International Geological Conference of 1891. John Edward Marr in his The Scientific Study of Scenery considered his book as, ‘an Introductory Treatise on Geomorphology, a subject which has sprung from the union of Geology and Geography’.
An early popular Geomorphic model was the geographical cycle or cycle of erosion model of broad-scale landscape evolution developed by William Morris Davis between 1884 and 1899. It was an elaboration of the uniformitarianism theory that had first been proposed by James Hutton (1726–1797). With regard to valley forms, for example, uniformitarianism posited a sequence in which a river runs through a flat terrain, gradually carving an increasingly deep valley, until the side valleys eventually erode, flattening the terrain again, though at a lower elevation. It was thought that tectonic uplift could then start the cycle over. In the decades following Davis’s development of this idea, many of those studying Geomorphology sought to fit their findings into this framework, known today as “Davisian”.
In the 1920s, Walther Penck developed an alternative model to Davis’s. Penck thought that landform evolution was better described as an alternation between ongoing processes of uplift and denudation, as opposed to Davis’s model of a single uplift followed by decay. He also emphasised that in many landscapes slope evolution occurs by backwearing of rocks, not by Davisian-style surface lowering, and his science tended to emphasise surface process over understanding in detail the surface history of a given locality. Penck was German, and during his lifetime his ideas were at times rejected vigorously by the English-speaking Geomorphology community. His early death, Davis’ dislike for his work, and his at-times-confusing writing style likely all contributed to this rejection.
Both Davis and Penck were trying to present the study of the evolution of the Earth’s surface on a more generalized, globally relevant footing than it had been previously. In the early 19th century, authors – especially in Europe – had tended to attribute the form of landscapes to local climate, and in particular to the specific effects of glaciation and periglacial processes. In contrast, both Davis and Penck were seeking to emphasize the importance of evolution of landscapes through time and the generality of the Earth’s surface processes across different landscapes under different conditions in a unified theory.
During the early 1900s, the study of regional-scale geomorphology was termed “physiography”. Physiography later was considered to be a contraction of “physical” and “geography”, and therefore synonymous with physical geography, and the concept became embroiled in controversy surrounding the appropriate concerns of that discipline. Some geomorphologists held to a geological basis for physiography and emphasized a concept of physiographic regions while a conflicting trend among geographers was to equate physiography with “pure morphology,” separated from its geological heritage. In the period following World War II, the emergence of process, climatic, and quantitative studies led to a preference by many earth scientists for the term “geomorphology” in order to suggest an analytical approach to landscapes rather than a descriptive one.
Quantitative Geomorphology
Part of the Great Escarpment in the Drakensberg, southern Africa.
This landscape, with its high altitude plateau being incised into by the steep slopes of the escarpment, was cited by Davis as a classic example of his cycle of erosion.
Geomorphology was started to be put on a solid quantitative footing in the middle of the 20th century. Following the early work of Grove Karl Gilbert around the turn of the 20th century, a group of natural scientists, geologists and hydraulic engineers including Ralph Alger Bagnold, Hans-Albert Einstein, Frank Ahnert, John Hack, Luna Leopold, A. Shields, Thomas Maddock, Arthur Strahler, Stanley Schumm, andRonald Shreve began to research the form of landscape elements such as rivers and hill slopes by taking systematic, direct, quantitative measurements of aspects of them and investigating the scaling of these measurements. These methods began to allow prediction of the past and future behavior of landscapes from present observations, and were later to develop into the modern trend of a highly quantitative approach to geomorphic problems. Quantitative Geomorphology can involve fluid dynamics and solid mechanics, Geomorphology, laboratory studies, field measurements, theoretical work, and full landscape evolution modeling. These approaches are used to understand weathering and the formation of soils, sediment transport, landscape change, and the interactions between climate, tectonics, erosion, and deposition.
Contemporary Geomorphology
Today, the field of Geomorphology encompasses a very wide range of different approaches and interests. Modern researchers aim to draw out quantitative “laws” that govern Earth surface processes, but equally, recognize the uniqueness of each landscape and environment in which these processes operate. Particularly important realizations in contemporary Geomorphology include:
1) that not all landscapes can be considered as either “stable” or “perturbed”, where this perturbed state is a temporary displacement away from some ideal target form. Instead, dynamic changes of the landscape are now seen as an essential part of their nature.
2) that many geomorphic systems are best understood in terms of the stochasticity of the processes occurring in them, that is, the probability distributions of event magnitudes and return times. This in turn has indicated the importance of chaotic determinism to landscapes, and that landscape properties are best considered statistically ‘The same processes in the same landscapes do not always lead to the same end results.
Source(s):
Wikipedia
Early Modern Geomorphology
