Cycle of erosion, davis and penk

Geomorphological cycle of erosion proposed by Davis and Penk

1. CYCLE OF EROSION : PROPOUNDED BY DAVIS AND PENK Presented by, RAJITH K 1 st Msc Geology University of kerala

2. INTRODUCTION Geomorphology : The study of landforms which is a composite result of different exogenetic activities operated on land surface Cycle of erosion : The balance between endogenetic and exogenetic activities in a cyclic process Exogenetic forces : ( Denudational forces) Forces operating on lithospheric surface and trying to eliminate the differences made by exogenetic forces

3. The above half of the circle shows exogenetic process, bringing the elevated land to the sea level .

4. Categories of denudational forces 1. Weathering : Process which makes bedrock either weak, fragmented or decomposed just near the earth surface ( In- Situ) or to a depth of few metres . Types are Physical and Chemical weathering . 2 . Erosion: Process which various erosive agents like running water, wind, glacier, sea waves and underground water obtain and remove rock debris from the earth crust and transport them for a long distance.

5. CYCLES OF EROSION At first William Moris Davis advanced the idea of “ Geomorphic cycle of erosion” He described and explained the distinctive characteristics possessed by the landforms. All the landscapes have definite life history after emergence. In this way through different stages the elevated land become featureless and flat plain known as Peneplain .

6. According to Davis, “The geographic cycle is the period of time during which an uplifted landmass undergoes its transformation by the process of land sculpture ending in low featureless plain.” Philip G. Worcester , accepted the geographic cycle but called it as the “Cycle of erosion”. According to him, “The cycle of erosion is the time required for streams to reduce newly formed landmass to base level”

7. Dvais describe the landscape as the function of structure, process and stage Structure : Means the nature of rock weather it is hard, soft, previous Process: Determines the type of erosion Stage : Denotes weather the landmass undergoing its transformation in young stage or in old stage

8. Davis assumptions, Each landscape has definite life history As soon as landmass emerged, erosional agents start their work on it. Finally formation of ultimate featureless surface For purpose of demonstrating his cycle, Davis imagined as an initial form a mass of land uplifted from beneath the sea by earth movements

9. The Stage of Youth The upliftment take place very rapidly The process of denudation starts on a stable mass If there is sufficient rain, a system of streams would quickly develop on the newly emerged surface The streams rapidly cut downwards and form deep valleys (“ V” shaped valley) Throughout the stage parts of the initial land surface would be preserved

10. Youth landscape Utah river

11. The Stage of Maturity Deepening of “V” shaped valley would have been slow down. Channels become nearer and nearer to “The base level of erosion”. Stream velocity would have been reduced. Condition of Grade of equilibrium (entire energy is used for the movement of water and its load). Vertical erosion slows down and horizontal erosion become dominant Gentle meanders, Flood plains

12. Mature landscape, Pennsylvania

13. The Stage of Old Age Landscape evolution become extremely slow in operation. Gradual reduction of river gradient, decline of stream energy and continued lowering of angle of valley. Continued to broaden their valley by meandering. By the end of old stage relief would assume to form very gentle, termed by Davis “ Peneplain ” The remaining isolated hills above the peneplain referred as “ Monadnocks ”

14. Meandering: Amazon river

15. Monadnock

16. REJUVENATION May be caused by epirogenic upliftment of a landmass accompanying tilting and warping. World wide lowering of sea-level also causes rejuvenation Knick point: The point of intersection of old and new base levels Greater the stream speed also cases rejuvanation

17. GRAPH OF DAVICIAN CYCLE

18. Positive aspects of Davis model Highly simple and applicable Very simple expressive language Based on detailed and careful field observations Came long time after Hutton’s concept. Capable of both predictions and historical interpretations

19. Negative aspects of Davis model Rapid rate of upliftment . Relationship between upliftment and erosion. Long period of crustal stability not possible. Dynamic equilibrium concept. Based only on observation; no instrumentation and measurement. Concept of grade not properly explained.

20. CONCEPT OF PENK ON CYCLE OF EROSION

21. Walter Penk German Geomorphologist Accepted the cycle of erosion Main critic of Davisian cycle Concept of phase, rate of uplift and degradation. According to Penck , the characteristics of landforms of a given region are related to the tectonic activity of that region.

22. The main postulates of Penks model, morphological characteristics of any region of the earth’s surface is the result of competition between crustal movement and denudation processes. Development of landscape is not time- dependent. Upliftment and erosion are always coexistent.

23. GRAPH OF PENKIAN CYCLE Case Uplitment Absolute height Relative relief First Active Increases Increases Second Active Increases Constant Third Active Constant Constant Fourth Finished Decreases Constant Fifth Finished Decreases rapidly Decreases

24. There was certain misunderstanding in the interpretation of Penck’s work as it was published in obscure German language. Penck’s morphological system was severely criticised in the United States in the same way the ‘geographical cycle’ was criticised in Germany. Penck’s concepts of parallel retreat of slope and continued crustal movements were subjected to severe criticism by many geomorphologists and geologists.

25. Davis cycle Penk's cycle 1. upliftment finished before Degradation starts. 1. upliftment and degradation strats together as soon as the landmass comes above the sea level. 2. The period of upliftment is small. 2. The period of upliftment May long or small or intermediately 3. The rate of uplift is very rapid. 3. different rate some times it is pride averge or slow also. 4. Landform is the result of structure , process and stage. 4. Landform is the result of the rate of uplift , rate of degradation and there lation ship in between these tow. 5. the start and end of the cycle is associated with three stages youth , mature and old. 5. He has not taken the stage into account but says three conditions of upliftment Aufsteigendo ( inereasing ) and geichformic (constant) Andabsteigende ( decreasing). 6. daives has not given more importance to dlope . 6. penk has more important Because it accelerates the rate of erosion and differentiate the landform. 7. There five cases , In first case relief inereases , and in second , third , and fourth it is constant and in the last fifth one it decreases . 7. In his case in the first two stage relief increases out of his three stage it decreases but never becomes constant . 8. Erosion does not exist in the first stage. 8. Erosion takes place in every stage and every cases . 9. He has assumed the last stage of cycle as the " peneplain " 9.He assumes the last stage as " Endrumpf " 10. His cycle over humid areas 10. His cycle over arid areas

26. THEORY OF L C KING

27. Based on his studies of landforms in arid, semi-arid and savanna regions of South Africa. He formulated a set of cyclic models (such as landscape cycle, epigene cycle, pediplanation cycle, hillslope cycle, etc.) and asserted that these are practicable in other parts of globe as well. Major landscapes in all the continents have been evolved by rhythmic global tectonic events. King’s concept of upliftment and crustal stability is similar to the concept of Davis.

28. Critique of Kings Model King’s model was limited to the African experience. It is doubtful to assert that there is uniform development of landscapes in different environmental conditions.

29. Gilbert’s Theory Grove Karl Gilbert “the landscape is the result of two competing tendencies i.e. tendency towards variability (when driving force exceeds resisting force) and tendency towards uniformity (when driving force equals resisting force)”. The three major components: concept of quantification, the concept of time and the concept of equilibrium.

30. CONCLUSIONS There is great difference between these two concepts developed by Davis and penk . Each concept is influenced by the landscapes of different regions. No individual concept is sufficient to explain all kind of landforms.

31. References Dr. Raad -Rahim hamood , cycle of erosion propounded by Davis and Penk computerative study, AL-Faith Journal. Chorley R. G. Beekinsal R P and dunnage (1973), the history of the study of landforms, Methuen and company limited, London. Thornbury W. D. (1969) Principle of Geomorphology , john wiley and sons , Ine . Newyork , PP. 99-208. Sparks B. W. (1972) Geomorphology , Longman Group Limited London The Division Geography cycle , PP , 7-21 Woreester P . G (1958) text Book of Geomorphology , D. van Nostrand company , Ine Newjercey , pp – 172 – 214