concepts of Geomorphology by Thornbury

Geomorphologic concepts by William D Thornbury

1. Concepts of Geomorphology RATHINAVEL K Reg No : 3382014 Ist M.Sc Applied Geology University of madras Guindy campus Chennai 25

2. 2 What is geomorphology ? Concepts in geomorphology Why do we need concepts ? Explanation of concepts Quick review of concepts Contents

3. As a word, geomorphology is composed of three Greek roots which are “ Geo , Morph & Logy ” that mean the “ Earth , Form & Science ” respectively. As a science , geomorphology is one of the branches of geology , dealing with the study of landforms of the earth, including submarine forms, their formation, developments and relation to the other geological factors. Geomorphology, studies in particular the  lithosphere , and interactions with the  atmosphere  and  hydrosphere , to understand the interconnection of various system processes. Geomorphology

4. 4 Geomorphology come about as a result of dissatisfaction with the term Physiography . Geomorphologists are particularly interested in the potential for  feedbacks  between climate and tectonics  mediated by geomorphic processes. ➼ geomorphic agents, such as river, wind, glacier and sea-waves, etc. ➼ geomorphic processes ; Erosion Transportation Deposition

5. 5 Why do we need Concepts ? Any discipline has concepts that are key for its progress. For geomorphology these need to be explicitly stated and consistently understood for what they are. They are a number of concepts will aid in the evaluation of much that follows in the subject “geomorphology", but also not only ones used in the interpretation of the landforms (landscapes). Some fundamental concepts are enumerated by W.D. Thornbury which comes into use in the interpretation of landscapes.

6. Concept no 1 ➼ This is the important principle of geology and is known as the Principle Of Uniformitarianism . It was first enunciated by James Hutton in 1785. According to Hutton " The present is the key to the past ". ➼ According to him geologic processes operated throughout geologic time with the same intensity as now ,We know that it is not true. “ The same physical processes and laws that operate today operated throughout geologic time, although not necessarily always with the same intensity as now ’’. Explanation:

7. 7 Pliestocene ice age, 10000 yrs ago Holocene (Recent ) Tectonic activities , climate , glaciers for example prove that the processes are not the same intensity Stream action in valley has the same intensity in the past and now

8. 8 ➼ There are numerous examples which shows that the intensity of various geologic processes has varied through geologic time. Dendrochronology

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10. 10 “ Geologic structure is a dominant control factor in the evolution of landforms and is reflected in them ”. Concept no 2 It is including such phenomena as : a - rock attitude (dip and strike). b - presence or absence of joints, faults, folds and bedding planes. c -physical hardness of the constituent of mineral d -permeability or impermeability of rocks.

11. 11 Control of geologic structure on landform Geological structures are, Folded structure Faulted structure Horizontal structure Vertical structure Domal structure

12. 12 FOLDED STRUCTURE

13. 13 HORIZONTAL STRUCTURE

14. 14 FAULTED STRUCTURE

15. 15 UNICLINAL STRUCTURE

16. 16

17. 17 DOMAL STRUCTURE

18. 18 VERTICAL STRUCTURE

19. 19 “ To a large degree the earth's surface possesses relief because the geomorphic processes operate at different rates ” . Concept no 3 Lithology and structure are major factors causing differential wasting of the earth surface Temperature, moisture, altitude, exposure, topography configuration, the amount and type of vegetation cover are factors causing changes in geomorphic processes within narrow limits.

20. 20 The rate of all weathering, all mass-wasting, all erosion, and all deposition varies appreciably within rather narrow limits in relation to the influence of local conditioning factors. variation in the climate condition between a (valley floor and hill top), (bare ground and hay vegetable cover) may be reflected the: Amount of precipitation Amount of soil moisture Rate and type of evaporation Temperature fluctuation above and below the freezing line.

21. 21 LESS EROSION = HIGH ALTITUDE LAND MORE EROSION = LOW ALTITUDE LAND POTENTIAL ENERGY = m x g x h (where m= mass, g= gravity and h= height)

22. 22 “ Geomorphic processes leave their distinctive imprint upon landforms, and each geomorphic process develops its own characteristic assemblage of land forms ”. The term ‘process’ applies to the many physical and chemical ways by which the earth's surface undergoes modification. In general endogenetic processes (originate from forces within the earth crust such as diastrophism and volcanism) tend to build up or restore areas which have been worn down by the exogenetic processes (results from external forces like weathering, mass wasting, erosion); Concept no 4

23. 23 Each geomorphic process develops distinctive landform Endogenetic Processes: Volcanic eruption, Tectonic movement, Earthquake, Tsunami Exogenetic Processes : Fluvial Process Glacial Process Aeolian Process Coastal Process etc. landforms have their individual distinguishing features depending upon the geomorphic processes responsible for their development, for example: A/ flood plains. Alluvial fans and deltas are products of stream action. B/ Sinkholes and cavern are produced by ground water. C/ Moraines are produced by glaciers.

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25. 25 “As the different erosional agents act upon the earth's surface there is produced an orderly sequence of land forms” . The land forms possess distinctive characteristics depending upon the stage of their development. This idea was most stressed by W. M. Davis and out of this idea grew his concept of geomorphic cycle and its concomitant stages of youth, maturity, and old age culminating in a topographic surface of low relief called peneplain . Concept no 5

26. A corollary to the concept of completed geomorphic cycle; is that of a partial cycle is accepted as a concept. Partial cycles are more likely to occur than completed ones, for much of the earth's crust is restive and subject to intermittent and differential uplifts.

27. 27 An orderly sequence of landforms by the act of geomorphic agent YOUTH MATURE OLD

28. “Complexity of geomorphic evolution is more common than simplicity”. ➼ Usually most of the topographic details have been produced during the current cycle of erosion, but there may exist within as area remnants of features produced during prior cycles. Commonly we are able to recognize the dominance of one cycle. ➼ Leland Horberg (1952 ) On the basis of origin of history, the landforms are divided into five groups: (1) Simple, (2) Compound, (3) Monocyclic, (4) Multicyclic And (5) Exhumed or Resurrected Concept no 6

29. 29 Simple landscapes are those which are the product of a single dominant geomorphic process. One energy and one erosional cycle Compound landscapes are those in which two or more geomorphic processes have played major role in the development of existing topography. More than one energy Monocyclic landscapes are those that bear the imprint of only one cycle of erosion; one erosional cycle

30. 30 Multicyclic landscapes have been produced during more than one cycle of erosion. Much of the earth's topography bears the imprints of more than one period of erosion. . More than one erosional cycle, e.g - dissected plateau, accordant summit level, multi planation surface Exhumed or resurrected landscapes are those which were formed during some past period of geological time, then buried beneath a cover mass of igneous or sedimentary origin, then still later exposed through removal of the cover. Due to denudational process, multi erosional cycle

31. 31 “ Little of the earth's topography is older than tertiary and most of it no older than Pleistocene” . The geologic structures are in general much older than topographic features developed upon them except in area of late Pleistocene and recent diastrophism Most of the details of our present topography probably do not date back of the Pleistocene, and certainly little of it existed as surface topography back of the tertiary. Concept no 7

32. 32 Age of the earth’s Topography 90% landforms are Tertiary and before Pleistocene era e.g.- Mountain, river, valley, lake etc

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34. 34 “ Proper interpretation of present-day landscape is impossible without a full appreciation of the manifold influences of the geologic and climatic changes during the Pleistocene ”. Pleistocene have had far-reaching effects upon present-day topography. Glaciation directly affected many million square miles, perhaps as much as 10,000,000 square miles, but its effects extended far beyond the areas actually glaciated. Glacial outwash and windblown materials of glacial origin extended into areas not glaciated, and climatic effects were probably worldwide in extent. Concept no 8

35. 35 Glaciated cover area 10,000,000 sq km. in Asia, Africa mainly North Pole Two aspect are very important Geology Climate ● Idea of geologic and climatic changes during Pleistocene is important

36. 36 Geology and Climate

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38. 38 Geology and Climate

39. 39 “ An appreciation of world climate is necessary to a proper understanding of the varying importance of the different geomorphic processes ”. Climatic variations may affect the operation of geomorphic processes either indirectly or directly. The indirect influences are largely related to how climate affects the amount, kind, and distribution of the vegetal cover. The direct controls are such as the amount and kind of precipitation, its intensity, the relation between precipitation and evaporation and daily range of temperature, whether and how frequently the temperature falls below. Concept no 9

40. 40 The climatic factors especially precipitation and temperatures influence the operation of the geomorphic processes

41. 41 Differencing climate is responsible for difference in geomorphic processes: Climate: Tropical(hot), Temparate (moderate), Polar(cold) Geomorphic processs : Fluvial, Aeolian, Costal, Glacial etc.

42. 42 Climate and Geomorphological Processes

43. 43 Climate and Geomorphological Processes

44. 44 “ Geomorphology, although concerned primarily with present day landscapes, attains its maximum usefulness by historical extension ”. Geomorphology concerns itself primarily with the origins of the present landscape but in most landscapes there are present forms that date back to previous geological epochs or periods. A geomorphologist is thus forced to adopt an historical approach if he is to interpret properly the geomorphic history of a region. The paleo -geomorphology covers the identification of ancient erosion surfaces and study of ancient topographies . Concept no 10

45. 45 Present day Landscape attains historical extension (Fossils, Human Skeleton, Dendrochronology etc) y

46. 46 Historical extension

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48. 48 Quick review of concepts

49. 49 Concept Description Alternatives 1. The same physical processes and laws that operate today operated throughout geologic time, although not necessarily with the same intensity as now Similar geomorphic processes that operate today operated throughout geologic time. Uniformitarianism 2.Geologic structure is a dominant control factor in the evolution of landforms and is reflected in them. Relatively frequent, modest-sized processes dominate in the progressive changing of the landscapes over long time periods. Gradualism 5. As the different erosional agents act upon the earth's surface there is produced an orderly sequence of land forms. Erosional agents on a planetary surface produce an orderly sequence of landforms as a function of time. Orderliness 4. Geomorphic processes leave their distinctive imprint upon land forms, and each geomorphic process develops its own characteristic assemblage of land forms. Landscapes reflect the influence of certain climatic processes by developing a characteristic assemblage of landforms. Morphoclimatic Zonation

50. 50 8. Proper interpretation of present-day landscape is impossible without a full appreciation of the manifold influences of the geologic and climatic changes during the Pleistocene. The geologic and climatic changes of the Pleistocene were critical in the shaping of most landscapes. Legacy of the  Pleistocene 10. Geomorphology, although concerned primarily with present day landscapes, attains its maximum usefulness by historical extension Geomorphology is primarily concerned with present- day processes that shape present-day landscapes. Modernism 6.Complexity of geomorphic evolution is more common than simplicity . It is necessary to search for simplicity in geomorphological systems. Simplicity 7 Little of the earth's topography is older than tertiary and most of it no older than Pleistocene. Most of the Earth´s topography is no older than Pleistocene. Youthfulness of Topography

51. 51 Principles of Geomorphology, II n d edition,(page 16-33) Thornbury W.D. (2002), CBS Publishers & Distributors, New Delhi, India Reference Guidance Dr. S. Umapathy , Retd . Prof. Jawahr Science College, Neyveli (NLC)