Geomorphic Landform Development theory of Davis | Normal cycle of erosion | By Ankit Sir

[@ritikushwaha20]

Geomorphic Theory of Davis William Moris Davis, American Geomorphologist First Geomorphologist to present a general theory of lamdform development. 1. Complete cycle of river life, in essay ' The Rivers And Valleys Of Pennsylvania ' in 1889 during Montana observation. 2. Geographical cycle in 1899 3. Slope Evolution Tried to explain sequential changes in landforms through time. Statement - "THERE ARE SEQUENTIAL CHANGES IN THE LANDFORMS THROUGH TIME (PASSING THROUGH YOUTH , MATURE AND OLD STAGES) AND THESE SEQUENTIAL CHANGES ARE DIRECTED TOWARDS WELL DEFINED END PRODUCT DEVELOPMENT OF PENEPLAIN ." TRIO OF DAVIS - LANDSCAPE IS THE FUNCTION OF STRUCTURE, PROCESS AND TIME. Every Landscape is result of these three factors. Structure - rock or lithological nature Time... Temporal context Process... Agents of denudation ( weathering and erosion) ASSUMPTIONS 1. Landforms are evolved products of the interaction of endogenetic and exogenetic forces. 2. The evolution of landform happens in an orderly manner in a sequence. 3. Streams erode their valleys rapidly downward until they achieve the graded condition. ( Maximum erosion occurs till the mean sea level or base level) 4. Short period of upliftment in landform. Upliftment occurs rapidly but erosion occurs slowly. 5. Erosion does not start until upliftment completes ( time dependent model - biggest criticism). STAGES OF RIVER EROSION 1. 1st stage... YOUTHFUL STAGE.... River/streams ( exogenetic force) passes through mountains. EROSION starts after the completion of the upliftment. Top surface of the summits are unaffected by erosion as rivers are still small and far apart, headward erosion occurs, leading to backwasting, stream lengthening occurs. Steep slopes - steep channel gradient - high velocity rivers - drilling action due to erosional tools - vertical erosion- depth of rivers increase - valleys deepen - V shaped valleys - deep and narrow valley -convex plane. Rapid rate of vertical erosion - High velocity, maximum erosion, big boulders, valley incision, pot holes, waterfals, rapids form. 2. MATURE STAGE... River reaches plain areas - speed reduces - wide area - meanders form - lateral erosion - integrated drainage network - low channel gradient - tributaries have reached base level of erosion - vertical erosion and valley deepening reduce - summits also erode - valley broaden - absolute as well as relative height of the mountain both decreases - rivers broaden, wide Valleys uniform in nature, transport capacity of rivers reduce due to low intensity and low channel gradient. 3. OLD STAGE... Low relief - total absence of valley incision, lateral erosion continues, valley widening continues, Water divide erodes, downwasting , backwasting, rapid rate of decrease of the absolute height Low kinetic energy - flat valley - concave slope - gentle slope, extensive flood plains, residual hills - MONADNOCK - low featureless plain - PENEPLAIN POSITIVE ASPECTS 1. Highly simple and applicable. 2. Lucid language 3. Observation based. 4. General theory of landform. 5. Capable of predictions and historical interpretation . 6. Synthesized the current geological thoughts ( base level by Powell) LIMITATIONS 1. Time dependent model ( upliftment completes then erosion starts). 2. Model requires long period of crustal stability for the cycle to complete. 3. Maximum focus on time rather than on Structure and process.

[@AmitNautiyal-q9t]

Very nice session.... Thank you sir

[@shreyakumarigupta12]

We love your teaching skill sir. Theory is very difficult to understand but you had made it esay for us. Thank you ! For your service.

[@GeographywithAnkit]

Most welcome Dear😊

[@viveksharma896]

Thanku sir . 🙏 very very helpful videos. 👏

[@prakhargupta8960]

Sir ye puchna tha ki ye jo youth mature and old age hai ye 1 he chain of mountains hai kya kyuki mature stage or old stage mein toh koi bhi mountain nhi hote hai

[@2023risingstar]

Thank u so much sir g

[@shyamalpal8311]

Target 2024 any one join ???

[@sandeepsabharwal3017]

Entropy?