The present status of geomorphology is the result of the gradual, but successive evolution of geomorphological thoughts postulated in different periods by innumerable philosophers, experts and geoscientists in the subject and outside the subject. Thus, the developmental phases of geomorphology indicate its dynamic nature. After taking its birth in the philosophical ideas of the ancient Romans and Greeks the subject has blossomed through the geomorphological methodological nutrients of the 18th and 19th centuries and reached its golden status in the 1st and 2nd decades of the 20th century with the postulation and wider acceptance of cyclic concept of landscape development and denudation chronology world over. After 1950, the science of geomorphology witnessed a major change in the methodological aspect in the form of rejection of Davisian model of cyclic development of landforms, introduction of quantitative methods in geomorphological studies, postulation of dynamic equilibrium theory of landscape development based on the concept of time-independent series of landform evolution, more emphasis on process geomorphology (process responsemodel), emergence of environmental geomorphology, shift from mega-geomorphology to micro-geomorphology, from longer temporal scale to shorter temporal scale, and more attention towards applied aspect of the subject.
Ancient Period
Though ‘geomorphology has developed from the work of late eighteenth and nineteenth century geologists and hydrologists’ (C.A.M . King, 1966), but some ideas regarding landforms were indirectly postulated even in the ancient period when philosophers and historians of Greece, Rome, Egypt etc., the principal seats of ancient culture and civilization, took the initiative in this precarious field. Herodotus(485 B.C.— 425 B.C), a noted Greek historian, made significant contribution in the field of rivers alluvial behaviour during his extensive journey of Egypt. After having a close observation of the depositional work of the Nile he postulated that ‘Egyp as the gift of Nile’. He further related the shape of depositional feature at the mouth of the river to Greek letter A and named this feature as delta. He also postulated that ‘there is gradual growth of delta towards the sea. On the basis of the presence of marine fossils in the alluvium of the Nile far inland he opined that ‘the level of sea is not permanent but there is occasional rise and fall when sea advances landward (transgressional phase) and retreats (regressional phase)’ Thus, we can infer the concept of transgressional and regressional phases of the sea from the statements of Herodotus.
Aristotle (384 B.C.— 322 B.C.), a reputed Greek philosopher, presented some very interesting ideas regarding water spring, origin of streams and behaviour of seas and oceans. According to him spring-fed streams are seasonal and ephemeral (nonpermanent). Limestones cannot maintain permanent surface drainage as most of the streams disappear and form subterranean drainage.’ According to him water springs get supply of water through (i) rainwater, which reaches underground through percolation and seepage, (ii) condensation of underground saturated air, and (iii) water vapour. He was also aware of changing nature of sea-level and deposition of eroded materials by the rivers in the form of alluvium. Strabbo (54 B.C— 25 A.D.). a noted historian, made significant contributions in the field of depositional work of the rivers. According to him the size and shape of delta depend on the nature of terrain through which the river makes its course. An extensive region having comparatively weaker rocks gives birth to larger delta as weak rocks through erosion yield more sediments to maintain large delta while the region of resistant rocks maintains smaller delta because resistant rocks are less eroded and hence produce less sediments. Thus, we may infer an indirect glimpse of the concept of differential erosion from the statements of Strabbo. Seneca maintained that ‘the rivers deepen their valleys through abrasion.’
It may be mentioned that some incoherent ideas were forwarded by ancient philosophers and historians but they could not collectively come to any definite conclusion.
Dark Age
With the fall of Roman empire a lull prevailed in the development of geographical as well as geomorphological thoughts for a very long period of 1400 years (from the first century A.D. to 14th century A.D.). Besides, some glimpses of geomorphological ideas put forth by few thinkers e.g. Aviecena (980—1037 A.D.), an Arabian thinker, broke the academic monotony. According to him mountains should be
divided into two categories i.e. (i) mountains originated due to upliftment and (ii) mountains originated due to erosion by running water.
Age of Catastrophism
The long-continued academic silence of 1400 years was suddenly broken by the emergence of catastrophists who believed in the quick and sudden origin and evolution of all animate and inanimate objects in very short period of time and thus new pages of peculiar and fantastic concepts were added to the treasure of geomorphological and geographical literature. The age of the earth was calculated to be a few thousand years. Only those events could be given cognizance which occurred in the life-time of the people. It may be pointed out that sudden endogenetic forces like volcanic eruption and earthquakes may be held responsible for convincing the thinkers to postulate such fantastic and unrealistic ideas not only related to the landforms, but to all of the animate and inanimate objects. The concept of sudden change and evolution also swept the biologists who believed in sudden evolution and destruction of all the living organisms.
Age of Uniformitarianism
The concept of catastrophism was finally rejected and gradual cyclic nature of earth’s history was postulated by James Hutton (1726—1797 A.D.) in the 18th century A.D. through his well-knit concept of uniformitarianism but the postulation of coherent scientific thoughts in the field of geomorphologv already began in the 15th, 16th and 17th centuries when the preexisting concept of everlasting (permanent) landforms was rejected and theirchanging nature through weathering and erosion was very much realized. Leonardo da Vinci (1452— 1519 A.D.) was of the opinion that the rivers formed their valleys themselves through vertical erosion and deposited the eroded materials elsewhere. Buffon (1707— 1788 A.D.) rejected the catastrophists’ postulation of very little age of the earth (thousands of years). He further opined that the rivers were the most powerful agent of erosion and they were capable of eroding the uplifted high land mass to sealevel. Targioni Tozetti (1712— 1784 A.D.), an Italian thinker postulated that the irregular courses (symmetry and asymmetry of the valleys) of the rivers depended on the nature of rocks through which they flow. The regions of massive and resistant rocks maintain deep and narrow courses (valleys) whereas broad and meandering courses are developed in the regions of soft and less resistant rocks. Thus, this concept gives the glimpse of differential erosion.
According to Guethard (1715— 1786 A.D.) not all the eroded sediments are deposited by the rivers in the seas rather some parts are also deposited in the courses of the rivers as flood plains. He also attached importance to the erosive power of the marine processes. Dimarest (1725— 1815 A.D.) was of the opinion that ‘the valleys through which rivers flow have been formed by themselves through the process of valley deepening’. He was probably the first to postulate the concept of development of landforms through successive stages. The 18th century appeared with a new wave of uniformitarianism on the academic stage of geomorphology, with James Hutton as its postulator. His concept of uniformitarianism is based on the basic tenet that the same geological processes which operate today operated in the past and therefore the history of geological events repeats in cyclic pattern. His concept of ‘present is key to the past9 aimed at the reconstruction of past earth-history on the basis of the present. According to him the nature is systematic, coherent and reasonable and thus destruction ultimately leading to construction indicates orderliness of nature. He was the first geologist to observe cyclic nature of the earth’s history. His work was published in the form of a research paper ‘theory of the earth: or an investigation of laws observable in the composition, dissolution and restoration of land upon the globe’ in the Transactions of the Royal Society of Edinburgh in 1788. Later on, his major work was published in the form of a book entitled, ‘Theory of the Earth with Proofs and Illustrations’ in two volumes in 1795. His concept, ‘that topography is carved out and not built-up’ is a significant contribution in geomorphology. John Play-fair (1748— 1819), a professor of mathematics and a close friend of Hutton, after making some suitable modifications to the Huttonian concept and adding some valuable contributions of his own elucidated Hutton’s views on uniformitarianism through his book entitled ‘Illustrations of Huttonian Theory of the Earth’ in 1802. Playfair also visualized the erosive and transporting powers of fluvial and glacial processes. On the origin of valleys Playfair was also far in advance of the views current at his time’ (C.A.M. King, 1966). Charles Lyell (1797—1873 A.D.), one of the most active followers of James Huttcn, laid the foundation of modern historical geology and he defined geology ‘as that science which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature.’ Most of his works appeared in his two books ; ‘Principles of Geology’(in two volumes) and T he Geological Evidences of the Antiquity of Man’ in 1863. C.G. Greenwood came to light through his paper entitled ‘rain and rivers : or Hutton and Playfair against Lyell and all comers’ in 1857 and was accepted as the father of modern subaerialism. ‘He put forward the idea of the base-level of erosion before Powell in America’ (C.A.M. King, 1966).
Modern Age (The Nineteenth Century)
Geomorphology became an independent discipline and a major branch of geology at the beginning of the 19th century when the development of geomorphic thoughts took place at regional level and two distinct schools of geomorphic thoughts can well be identified e.g. (i) European School and (ii) American School.
(A) European School— Significant contributions were made in the fields of recognition and identification of Pleistocene Ice Age and glaciation, glacial erosion, marine erosion, fluvial processes and erosion, arid and karst landscapes. Sir Charls Lyell ( 1797— 1873 A.D.) not only endorsed the concept of uniformitarianism put-forth by James Hutton but also popularised the concept through his books, ‘Principles of Geology (two volumes). His significant contributions in biology became the base of ‘p rig in of S p ecies’ of Charles Darwin. His book entitled, ‘The Geological Evidences of the Antiquity of M an’ (published in 1863) accommodated most of the concepts of Hutton. Credit goes to European school of geomorphology for identification and recognition of ice ages. The geoscientists collected sufficient and convincing evidences in support of total glaciation of northern Europe during Pleistocene period. Louis Agassiz (1807— 1873 A.D.) is given credit for an early start in this precarious field. Though Jean de Charpentier postulated his concept of continental glacier and ice ages in 1841 but Agassiz is given credit for the recognition and identification of the presence of ice age during Pleistocene period as he presented his ideas in 1840. They opined that m ost parts of northern Europe were covered with thick sheets of continental glaciers during Pleistocene period. It may be mentioned that the process of study of glaciation was started much earlier by John Playfair in 1815; Venetz of Switzerland in 1821 and 1829, Norweigian scholar Esm ark in 1824, German scientist Bernhardi in 1832, Jean de Charpentier of Switzerland in 1834 than Louis Agassiz. The Scottish geologist Jam es Geikie studied different aspects of ice age and published his ideas through his book entitled. ‘The Great Ice A ge’ in 1894. A ccording to him an ice age involving longer geological period of time is comprised of distinct several glacial periods which are separated by warm interglacial periods. A Penck and Bruckner after their observations of Pleistocene glaciation over the Alps identified four glacial periods during Pleistocene ice age e.g. Gunz, Mindel, Riss and Wurm which were separated by three warm interglacial periods.
In the field of m arine erosion, corrasion by sea waves was given more attention and importance. Sir Andrew Ramsay (1814— 1891) presented detailed description of marine platforms made by marine erosion in Wales and S.W. England. It may be mentioned that previously Ramsay attached more significance to murine abrasion hut in Inter part ol his life he gave more importance to Hu vial erosion. Baron Ferdinand N on Richthofen (1833— 1905) made significant contributions in the field ol marine erosion during his visit to China. He ‘produced his work on the genetic treatment of landforms, in which he supported a marine origin for plains found beneath marine transgressions, these being produced when sea-love I is rising slowly’ ( C A M . king. 1966). C. G, Greenwood, a British geologist, made significant contribution in the field of subacrial erosion. He is considered to be the first geoscientist to postulate the concept of base level of erosion even before Major Powell in the U.S.A. Jukes (1862) divided rivers into two categories e.g. (i) transverse streams which flow across the geological structures and (ii) longitudinal streams which follow the direction of strikes of rock beds or (low parallel to the geological structures. According to him longitudinal streams are subsequent to transverse streams i.e. transverse streams originate prior to longitudinal streams. Jukes also described various aspects of river capture.
(B) American School— American school is credited for making maximum contributions in the field of geomorphology. In fact, the last two decades of l^th century and first two decades of 20th century (i.e. from 1S75 to 1920) are considered as ‘golden age’ not only of American geomorphology but also of world geomorphology because it was this period when for the first time general theory of landscape development was propounded by VV.M. Davis and the landform analysis attained its final shape. The concept of sequential changes of landforms through successive developmental phases in terms of time based on the basic tenet of time-dependent concept of Divisian model of geographical cycle of erosion became the core of landform analysis and guide-line for geomorphologists and geologists not only in North America but world over. Powell, Gilbert, Dutton and Davis made significant contributions in the field of subaerial denudation. M ajor J.W . Powell (1834— 1902 A.D.), a major in American army after a thorough study of Colorado plateau and Uinta mountains (1876) suggested geological structure as a basis for the classification of landforms. He attempted a genetic classification of river valleys and consequently classified them into antecedent, superimposed, consequent vU||cys etc. His most significant contribution is the postulation of lim it of maxim u m vertical erosion (valley deepening or downcutting) by streams to which he proposed the term of base level, which is determined by sea-level. Later on, C.A. mallot (1928) inferred three types of base level from his writings viz. ultimate, local and temporary base levels. He also opined that if the fluvial processes (streams) were allowed to erode the landmass uninterruptedly for fairly a long period of geological time the high landmass might be eroded down to a level plain which may be slightly above the sea level. This erosional level plain was later termed by Davis as peneplain. He also observed the nature of narrowing and shifting of water divides through the process of lateral erosion. G. K. G ilb ert (1843— 1918 A.D.) is considered as the first real geomorphologist of America because ol his significant contributions in systematic and quantitative geom orphology. In fact, he was much ahead of his lime and postulated such concepts which still hold today. ‘He stressed the importance of creative imagination, of testing a number of hypotheses, and of analogies in the field of geomorphology’ (C.A.M. King, 1966). Gilbert never preferred to be called as theoretician rather he took himself as an investigator. A fter a thorough study of different localities of America (e.g. Great Basin, Bonnevile Lake, artesian wells of Great Plains, Henry Mountains, Siera Mountains etc.) he propounded a number of laws i.e. law of uniform slope, law of structure, law of divides, law of increasing acclivity, law to tendency to equality of actions, dynamic equilibrium, law of the interdependence etc. He was the first geoscientist to propound the concept of graded profile of a river and to establish relationship among load, volume, velocity and channel gradient on the basis of quantitative analyses of these variables. His contributions have been elaborated in much detail in the 3rd Chapter of this book.
C. F. Dutton (1843— 1912 A.D.) was the first geoscientist to use the term isostasy to denote equilibrium condition of upstanding and downstanding landmasses of the earth’s surface. During his study and investigations of Colorado Plateau and Grand JCanyon of the Colorado river he opined that the present canyon was the result of long continued period of fluvial erosion to winch he assigned ihe term of the period of great denudation. He also presented pieces of evidence in support of Powell’s concept of base level of erosion.
W.M. Davis (1850— 1934) was a professor of physical geography at Harward University. He is considered to he the patron of the science of geomorphology because of his significant contributions in different fields of geomorphology and for giving new direction to landform study. He covered almost every nook and corner of geomorphology. He is given credit to systematize and integrate hitherto seaitercd ideas of American geomorphologists to present them in coherent and well defined framework. His contributions were so significant and lie was so dominant among the American geomorphologists that the American school of geomorphology was recognized as Davisian school of geomorphology. Davis is credited for the postulation of first general theory of landscape development which, is in fact, a synthesis of his three major concepts viz.. complete cycle of river life (1889), geographical cycle (1899) and slope evolution. He emphasized progressive development of erosional stream valleys through the concept of complete cycle of river life while sequential changes of landscapes through time involving historical evolution of landforms (time-dependent series of landforms) or cyclic development of landforms were highlighted through the concept of geographical cycle. ‘The reference system of Davisian model/theory of landscape development is that the landforms change in an orderly manner as processes operate through time such that under uniform external environmental conditions an orderly sequence of landforms develops’ (Robert C. Palmquist). Since Gilbert and Davis also stepped in the 20th century, and hence their further contributions to geomorphological thought are considered in the succeeding heading. Further, the contributions of Davis will be elaborated in detail in the 3rd chapter of this book.
Modern Age (The First Half of the 20th Century)
The beginning of the 20th century was heralded by methodological revolution in geomorphological studies brought in by W.M. Davis
and his followers at home (UiS.A.) and abroad aW. Penck in Germany. His classical model of geographical cycle propounded in 1899 and defined by him ‘as a period of time during which an uplifted landmass undergoes its transformation by the processes of land sculpture ending into a low featureless plain (peneplain)’ dominated the geomorphological investigations all over the world throughout 1st half of the 20th century inspite of its stiff opposition by W. Penck and others in Germany. His model of geographical cycle was variously termed, popularised and applied by his followers world over e.g. normal cycle, erosion cycle, geomorphic cycle, humid cycle etc. It may be mentioned that his ‘geographical cycle’ does not represent his general theory of landscape development as his general theory states ‘that there is sequential change in landforms through successive stages and the changes are directed towards a definite end i.e. attainm ent of featureless plain (peneplain)’. The main goal of his theory was to present systematic description and a gcnetic classification of landforms. Davis also identified 3 basic factors which control the evolution of landforms viz. ‘landscape is a function of structure, process and tim e’, which are termed as ‘trio of D avis’. His concept of geographical cycle was later on applied with all other (other than fluvial) processes by Davis and his followers e.g. arid cycle of erosion (Davis, 1903, 1905 and 1930), glacial cycle of erosion (Davis, 1900 and 1906), marine cycle of erosion (Davis, 1912, D.W.
Johnson, 1919), karst cycle of erosion (Beede, 1911, Cvijic, 1918), periglacial cycle of erosion (L.C. Peltier, 1950). His model was modified and presented in revised forms by a few geomorphologists after 1950. Davis concept of historical evolution of landscape became the pivot for the classical concept of denudation chronology and erosion (plantation) surfaces in U.K. Davis’ major contributions (research articles, papers and addresses) were published in a book form entitled ‘G eographical Essays’ in 1909. He is considered as a great definer, analyser, interpreter, systematiser and synthesiser.
Only two quotes from S.W. Wooldridge and S. Judson that ‘Davis towers above his predecessors and successors, like a monadnock above one of his own peneplains’ (S.W. Wooldridge), and ‘his grasp of time, space and change, his command of detail, and his ability to order his information and frame his arguments remind us again that wc are in the presence of a giant’ (Sheldon Judson. 1975) are sufficient enough to demonstrate the greatness of Davis in the enrichm ent and advancement of geomorphological knowledge. C.G. Higgins’ (1975) remark that ‘Davis’ rhetorical style is justly admired and several generations of readers became slightly bemused by long though mild intoxication on the limpid prose of Davis’ remarkable essays’ speaks of the academic calibre of W.M. Davis.
The American school of geomorphology was further entriched by significant contributions of a host of geomorphologists e.g. D.W. Johnson (marine process and coastal geomorphology), C. A. Malott (fluvial processes and erosion), H.A. Mayerhoff and E.W. Olmsted (evolution of Applachian drainage), R.P. Sharp. C.P.S. Sharp. A.K. Lobeck, W.D. Thornbury etc. During the 1st half of the 20th century European school of geomorpholgy made significant contributions in the advancement of geomorphological thoughts. British geomorphologists made their independent identity and there emerged an entirely different school of geomorphology which laid emphasis on the chronological study of landscape development in historical perspective better known as denudation chronology based on the concept of palim psest S.W. Wooldridge (his famous book being the Physical Basis of Geography : An Outline of Geomorphology, published in 1937), J.A. Steers (The Unstable Earth, published in 1832) etc. made significant contributions in different branches of geomorphology.
The Davisian model of geographical , cycle met with strong criticism and his concept of rapid and erosionless upliftment became the crux of criticisms by the opponents of cyclic concept of the evolution of landforms particularly by the German geoscientists. The German critics of Davisian model of cycle of erosion fall in two categories viz. the first category of opponents pleaded for outright rejection of cyclic concept while the second category of critics suggested modifications and presented entirely new model. According to Penck landform developmentis not time-dependent as envisaged by Davis rather it is time-independent.
W. Penck, through his ‘Morphological Analysis’ and ‘Morphological System’ tried to reconstruct and interpret past events of crustal movements on the basis of exogenetic processes and morphological characteristics. The reference system of Penck’s model of landscape development is that the characteristics of landforms of a given region are related to the tectonic activity of that region. The landlorms, thus, reflect the ratio between the intensity of endogenetic processes (i.e. rate of upliftment) and the magnitude of displacement of materials by exogenetic processes (the rate of erosion and removal of materials). According to Penck landforms development should be interpreted by means of ratios between diastrophic processes (endogenetic or rate of upliftment) and erosional processes (cxogen^tic, or rate of vertical incision). ‘Penck is supposed to have deliberately avoided the use of stage concept in his model of landscape development either to undermine the cyclic concept of W.M. Davis or to present a new model’ (Savindra Singh, 1995). In the place of Davis’ stage, he used the term entwickelung meaning thereby development. In the place of youth, mature and old stages he used the terms aufsteigende entwickeling (waxing or accelerated rate of development), gleichformige entwickelung (uniform rate of development) and absteigende entwickelung (waning or decelerating rate of development). A detailed account of Penck’s contributions will be presented in the third chapter of this book.
A new branch of geomorphology in the form of climatic geomorphology was developed in France and Germany on the basic tenet that ‘each climatic type produces its own characteristic assemblage of landforms’. Sauer (1925), Wentworth 1928), Saper (1935), Friese (1935) etc. paved the way for the postulation of the concept of climatic geomorphology and m orphogenetic or morpho climatic regions by Budel (1944, 1948) and L.C. Peltier (1950) in Germany. This concept of climatic geomorphology was further advanced and established by Tricart and Cailleux in France in the 2nd half of the 20th century.
The statistical techniques were first introduced by Krumbein in geology in 1930s and the work ol American engineer R.E. Horton (1932 and 1945) brought quantitative revolution in the field of geomorphology when he presented quantitative analysis to morphometric characteristics of fluvially originated drainage basins. The criticism of Davisian model of landscape development and descriptive geomorphology gained currency after 1940 and siren was raised for the rejection and replacement of time-dependent evolutionary concept of landscape development. It may be mentioned that at a time (1950) when majority of the geomorphologists world over became fed up with evolutionary model to Davis and pleaded for alternative theory of landscape development which may envisage time-independent series of landforms Pelltier presented the concept of periglacial cycle of erosion in 1950 in Germany which offered support to Davisian model of cycle of erosion.
Modern Age (The Second Half of the 20th Century)
Post-1950 geomorphology has undergone seachange in the methods and approaches to the study of landforms, conceptual framework, paradigm and thrust areas of study. The recent trends in the field of geomorphological studies since 1950 include increasing criticism of Davisian model of cyclic development of landforms, concerted efforts for the replacement of cyclic model by non-cyclic (dynamic equilibrium) model, descriptive geomorphology (qualitative treatment of landforms) by quantitative geomorphology, inductive method of landform analysis by deductive method, introduction of models and system approach, emergence of process geomorphology, climatic geomorphology, applied geomorphology, environmental geomorphology, shift from larger spatial and longer temporal scale to smaller spatial and shorter temporal scale etc.
The decade 1950— 60 was devoted more for the quantitative study of landforms and processes and the consideration of geomorphic theories occupied a back seat. This is the reason that a set of basic concepts of ‘the landscape cycle, the epigene cycle’, ‘the pediplanation cycle’ and ‘hillslope cycle’ postulated by L.C. King and his ‘Canons of Landscape’ (published in 1953) could not win support. The rejection of Davisian concept of ‘cyclic m odel’ based on ‘time dependent landform evolution’ culminated in the postulation of ‘dynamic equilibrium theory’ of landscape development by J.T.Hack, R.J. Chorley and others based on the concept of ‘time-independent evolution of landscape’, and ‘system concept’.
The landscapes were taken as open systems which are in steady state of balance through continuous input of energy and matter and output of matter. Though Hackian model of landscape development envisaged landscapes as the result of balance between the resisting force of geomaterials and erosive force of the geomorphological processes acting on them but he laid more emphasis on geological control as he opined that ‘differences and characteristics of forms are explicable in terms of spatial relations in which geologic patterns are the primary consideration’ (Hack, 1960). It may be pointed out that even Hack could not escape from evolutionary concept as he himself admitted ‘that evolution is also a fact of nature and that the inheritance of form is always a possibility’ (Hack, 1960).
R.C. Palmquist has opined that ‘Hack (1965) paraphrases Davis’ ideal geographical cycle in terms of equilibrium concept and develops a similar evolutionary scheme. An initial disequilibrium stage (youth) of rapid stream incision is followed by an equilibrium stage (mature) wherein the rounded interfluves are lowered as potential energy decreases though they do not change in form’ (R.C. Palmquist). It may be mentioned that continued criticism of cyclic model of landform development and ultimately its rejection caused a conceptual vacuum, which could not be filled up even by dynamic equilibrium theory. Recently, a few alternative geomorphic theories have been advanced e.g. ‘geom orphic threshold model’, ‘tectonic-geom orphic model’ (M. Morisawa), ‘episodic erosion model (S.A. Schumm) etc.
The most outstanding contribution to the advancement of geomorphological knowledge in this period is the adoption of quantitative approach based on deductive scientific method of the study of landforms and processes at short spatial and temporal scales. The time factor which was taken as a process in the landscape development in the cyclic model has now been accepted as a variable. The maga and meso-scales used for landform studies have now been reduced to micro-scale wherein the mechanism of processes can be properly understood through field instrumentation and measurement of the mode and rate of operation of geomorphic processes. Thus, ‘form geom orphology9 has been replaced by ‘process geom orphology*. This quantitative approach resulted in the formulation of functional theory of landscape development’ which lays more emphasis on the logical analysis of the relationship between ‘forms’ and related ‘processes’ based on quantitative data derived through filed instrumentation. The post-1950 geomorphology was also enriched by the introduction of system theory for the explanation of landforms and processes and postulation of different geomorphic models e.g. natural analogue system, physical system and general system. The process-response model has became the focal theme of process-geomorphology.
Another significant contribution is the emergence of environmental geomorphology which is, in fact, significant aspect of applied geomorphology, which envisages application of geomorphic knowledge for the removal of environmental problems arising out of interactions – of economic’ and ‘technological man’ with geomorphological processes and natural system. For example, monitoring of fluvial processes in man-impacted gully basin (cultivation) enables the investigator to ascertain the mode and rate of rill and gully erosion, siltation and loss of soil and to suggest remedial measures (Savindra Singh’s study, 1996).
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