chapter 7-Geomorphologic processes and land features.pptx

chapter 7-Geomorphologic processes and land features.pptx

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  Geomorphologic processes and landfeatures
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  3.1. Introduction •Geomorphology isthe science that studies the surficial processes operated on the earth and the landform nature, origin, and interrelationships formed by the processes. •Geomorphologic processes are processes that are operated on the surface of the earth resulting different landforms. •There are broadly two types of geomorphic processes. These are:- 1. Endogenic processes, e.g. volcanism. 2. Exogenic processes, e.g. Weathering, mass wasting, erosion and deposition. • Rivers, wind, moving ice and sea waves are agents of geomorphologic processes.
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  3.2. Geomorphologic processesof rivers (streams) •Surface water flowing in channels of their own are defined as streams. •A large stream flowing through extensive area and receiving water from smaller side streams is distinguished as river. •During its life from head to mouth regions the stream water performs geological work, which can be studied under 3 phases. •These are erosion, transportation, and deposition.
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  3.2.1. Erosion byriver •Erosion is the disintegration of the rock by a natural agent through mechanical, chemical processes accompanied by removal of disintegrated product from its original place. •Streams or rivers cause erosion in 4 ways: 1. by abrasion 2. by attrition 3. by hydraulic action 4. by chemical action (corrosion)  The rate of stream erosion depends on a number of factors.  These are (a) velocity of stream (b) lithology (c) load carried by stream.  The velocity of stream depends upon channel size, channel shape, channel gradient, discharge and load.
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  3.1.2. River transportation •Riversare very powerful transporting geological agents. •The amount of solid material transported by a river is called load. •Load is transported by a river in 3 ways. (a) As dissolved load: this comprises all soluble matter in the stream water in solution form. (b) As suspended load: this consists of silt, clay, fine sand etc. Such load is carried by the river in suspension form. (c) As bed load-The bed load comprises heavier particles of sand, pebbles, gravel, etc, which are transported mainly by their rolling, skipping, gliding along the bottom of the stream.  This kind of movement of load is discontinuous and slow.  The process of intermittent jumping of stones is called saltation.
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  3.1.3. River deposition •Depositiontakes place whenever geological agents lose energy. •The separation of materials takes place automatically as the larger and heavier particles settle quickly while the smaller and the lighter ones continue their journey farther a head. •The material that a stream deposits as sediment is called Alluvial or Alluvium deposits. •The term alluvium means sediment deposited by a stream. •It contains fine material such as silt, clay, coarse sand and gravel. •There are 5 types of river deposits. These are:
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  A. Alluvial fans:The alluvial materials that flow down from mountains accumulate at the foot of hills where the stream enters a plain.  The deposition occurs due to the abrupt change in the gradient of a river valley.  Such deposits spread in the shape of FLATE FANS in which the apex points uphill.  Usually the coarser material is dropped near the base of the slope while the finer material is carried farther out on the plain.
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  B. Flood plainsdeposits: During flooding a river over flows its banks and submerges the adjacent low-lying area where deposition of alluvial material takes place. • A wide belt of alluvial plain formed in this way on either side of the stream is called FLOOD PLAIN. • Flood plain gets submerged only when a river overflows its bank at flood stage.
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  •(3) Natural levees:These are low ridges that are formed on both sides of a river channel by the accumulation of sediments along the banks. •This is because river water suffers first check in velocity on the banks while over flowing them. •Development of such levees by flooding causes raising of the banks. •These structures are sometimes become helpful in preventing floods of previous intensity. •As result, most of the coarse sediment is deposited along the area bordering the river channel and the finer sediments are deposited more widely over the flood plain.