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IAS Geography Notes: Erosion and Deposition - Action of Running Water and Groundwater

Last Updated - August 23, 2017

Geography is one of the most chosen subject in IAS Exam, owing to its limited syllabus and interesting topics. Endogenic and Exogenic forces in Geography is among the most important sections generally asked in Civil Services. Candidates appearing for upcoming Civil Services exams are advised to go through the notes and important pointers mentioned in the article about pattern of IAS and it’s section. Through this post we will be knowing about the geomorphic agents – running water and ground water.

The equilibrium or isostasy on the surface of the earth is the result of balancing of various exogenic and endogenic forces on its surface. The endogenic forces originate below the surface of the earth due to tectonic activities and magma flow beneath the surface. These endogenic forces have created several 1st order and 2nd order relief features such as oceans (1st order), continents (1st order), volcanoes (2nd order), mountains (2nd order), hills (2nd order), etc on the earth’s surface.

However, the exogenic forces have their origin above the surface (in the atmosphere) and are associated with the creation of 3rd order relief features over the surface of the earth. Sun is the major source of channelization of this exogenic forces. The movement of the sun (from one solicit to other) effects climatic conditions which further regulate temperature, precipitation, and humidity and hence influence the agents of these forces.

Weathering, erosion, transportation, and deposition form the entire cycle of denudation process which entails the entire mechanism of exogenic forces on the surface of the earth. Water is a major agent of exogenic forces, both the river water and ground water, play a decisive role in shaping various erosional and depositional features on the surface of the earth.


Effects of running water

The flowing or running water has two components. One is the rivers and streams which are linear flow and other is on overland flow that is on the general land surface.

The flow over the surface causes the sheets of soil getting removed in a gradual manner. The process might not be visible on level surfaces as the rate of erosion is quite slow. However, on steep slopes like hills and mountains, the process of erosion is easily noticeable due to accelerated rate of movement of water. This type of erosion is termed as Sheet Erosion and is prominent in degrading the productivity of the land.

The process of Sheet erosion carries away with it the productive layer of soil which contains minerals and organic material. The intensification or continuation of sheet erosion leads to the development of gullies which further deepen to form valleys if the process continues for a long time. The process of continuation of sheet erosion leading to the formation of gullies is known as Gully erosion.

After the formation of the valley, the gap is filled by a stream of water (of the the river flowing in the region) which continues to flow through it. This entire process of erosion affects the topography of the surface and makes it unfit for cultivation. The ravines caused by the river Chambal are good examples of badland topography

Read:IAS Geography Notes: Earthquakes


Course of the river and its subsequent effect on erosion

The course of flow of the river has a major effect on the process of erosion of the surface through which it flows. The course of the river is divided into three parts upper, middle and lower. We take a look at the effects of each course of flow on the process of erosion.

Upper Course

It begins where the river originates. Generally, the river originates from the top of a hill, mountain, or glacier where the effect of erosion is at its peak.

The river flows down the steep slope of hills or mountains and gains velocity on its path (by virtue of losing its height steeply). This fast flowing water exerts an enormous force on the surface of its flow thus, intensifying the process of erosion.

Due to the effect of this high magnitude erosion deep cuts are formed on the surface which paves the way for the formation of valleys. Gorge, high-velocity waterfalls are some common features associated with this course of flow.

Middle course

Lateral erosion which was observed during the upper course of the river flow gradually gets replaced with vertical erosion at this stage.

Volume of water increases with the confluence of many tributaries. Unlike the upper course, streams are plenty and are in good integration with each other.  

Transportation of eroded material from the upper course takes place resulting in the formation of alluvial fans, alluvial plains, meanders etc.

Lower course

At this stage the river flows in a broad and more level type of surface as compared to the above two course.

The debris and sediments from the upper and middle course are bought down at to the surface.

Vertical erosion ceases, whereas lateral erosion goes on.

The the river at this stage of its flow helps in building up of depositional features. Floodplains, meanders, deltas, oxbow lakes etc. are common features at this stage of the river flow.


Erosional landforms

Valleys, Georges, Canyon

Valleys, Georges, Canyon
  1. The force of running water exerts enormous pressure (during the upper course) on the surface on its path to facilitate its flow. The gullies widen into valleys and are occupied by the stream of water.
  2. A deep valley with a very steep side (or straight side) is known as Gorge.
  3. A canyon is characterized by a step-like slope and may be as deep as that of a gorge.

 

Potholes, Plunge pools

Potholes, Plunge pools
  1. Potholes (shown in above picture) are depression over the rocky beds which are more or less circular in shape.
  2. Once a shallow depression is formed pebbles and boulders accumulate in it and get rotated by the flow of water. This rotatory motion widens the gap and creates potholes.
  3. Plunge pools are deep potholes which are commonly found at the foot of a waterfall.
  4. The sheer impact of water and rotation of boulder is the cause of their formation.

Depositional landforms

Alluvial Fans

Alluvial Fans
  1. These landforms are formed during the middle course of the river flow, generally at the foot or slope of the mountain.
  2. The main reason behind their formation is the loss of energy of the river stream as it moves from upper to middle course.
  3. They are spread as broad low to high deposits of cone-shaped

Deltas

Deltas
  1. These are similar to alluvial fans except the fact that the develop at different locations.
  2. They are formed at the mouth of the river which is the final location for deposition of carrying sediments.
  3. Deposits here are well sorted with clear stratification which is unlikely for alluvial fans.
  4. The coarse material like silt and clay are carried out into the sea.

Erosional features due to Ground water

Ground water is another important agent of exogenic force which is responsible for creation of various depositional features. It is that part of surface water (rain-water or snow melting) that accumulates in the rocks afterseeping through the surface. The rocks that allow the water to pass through them are called permeable rocks. The ground water accumulation takes place with the help of this type of rocks. Rocks that resist the passage of water under the surface are known as impermeable rock. Let’s take a look at erosional feature formed due to the effect of ground water

Sinkholes

Sinkholes
  1. Medium to small sized rounded to sub-rounded shallow depression on the surface of rock known as swallow holes.
  2. A sinkhole is an opening more or less circular at the top and funnel-shaped towards end.
  3. A sinkhole formed solely through the action of solution is called solution sink.
Caves

 

  1. This another major type of depositional feature that is formed by the action of ground water in the areas where there are alternative beds of rocks(non-porous) with limestone or dolomite in between or in areas where limestone are dense, massive and occurring as thick beds.
  2. Caves normally have single opening through which streams are discharged. A cave with opening at both ends is called tunnel.

There are many other depositional and erosional landforms on the earth’s surface which are formed by the action of running water. This includes meanders, floodplains, oxbow-lakes, braided channels etc. Here we have restricted ourselves to the discussion of most prominent landform features which are generally observed. You can comment below the topics for which you require us to prepare notes. Till them keep revising and study smartly.


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