AGENTS OF EROSION -1

MADE BY•AASTHA•SHRUTI•RACHANA•VASUNDHARA•MOHINI•AISHWARYA•MRUNAL•ASHMITA•VAISHNAVI•REVATI

PROJECT OF GEOGRAPHY

WATERis the most important erosional agent and erodes most commonly as running water in streams. However, water in all its forms is erosional. Raindrops (especially in dry environments) create splash erosion that moves tiny particles of soil. Water collecting on the surface of the soil collects as it moves towards tiny rivulets and streams and creates sheet erosion. In streams, water is a very powerful erosional agent. The faster water moves in streams the larger objects it can pick up and transport. This is known as critical erosion velocity. Fine sand can be moved by streams flowing as slowly as three-quarters of a mile per hour. Streams erode their banks in three different ways: 1) the hydraulic action of the water itself moves the sediments, 2) water acts to corrode sediments by removing ions and dissolving them, and 3) particles in the water strike bedrock and erode it. The water of streams can erode in three different places: 1) lateral erosion erodes the sediment on the sides of the stream channel, 2) down cutting erodes the stream bed deeper, and 3) headward erosion erodes the channel upslope.

AGENTS OF EROSION-1

RIVERRiver at its young age that is near the source is very strong and it cuts down the soil and rock along its course. Picture to the right gives a good example of river erosion .River, glacier & wind are main agents of erosion. In this we will see the erosion of river..

EROSIONThe beds of the river as well as its banks are cut by the speedily flowing stream of water as well as the load moving with it.Moreover, the sand, stone, etc in the flow also break as they collide. The following landforms are formed due to these processes of erosion.

GORGEIn mountainous areas, a river flows with a great speed. Therefore, the bed of the river gets eroded more than its banks. This gives rise to a gorge that has steep banks and narrow bed. For example, the gorges of river vaitarna in thane district and the river ulhas in raigad district.

A V-shaped valley, on land or in the ocean, is just as it sounds: a valley in the shape of a V, with steep sides and short tributaries entering into the main valley. They are formed by streams or ocean currents that cut in a downward motion, narrowing the valley into its characteristic shape. Over time, the V-shape may become broader, forming a V-shaped valley.

1 2 3

1.The river cuts down and deepens its valley.

2.The river widens its valley as it deepens it.

3.The river continues to widen its valley.

‘V’ SHAPED VALLEY

POTHOLESThis is about river potholes, bowl-shaped features that have been scoured out of river beds by swirling pebbles in a fast-flowing river. (These are not related to the kind of potholes (really called swallow holes) found in areas of limestone and which are the entrances to caves.) Large potholes are rather rare, although many mountain rivers, or those with very steep courses, do have examples of medium sized potholes. Potholes are best seen when the river is low. You will find many valleys in western ghats.

WATERFALLA waterfall is a natural formation which is formed when a water body such as a river breaks the rocks underneath it and causes them to erode. The erosion will then break the elevation of the river causing the river to fall from a height. The elevation keeps breaking as the years go by which makes the waterfall. Ultimately, the soft rock collapses and only the hardrock remains causing the water to fall from a height. There are many different types of waterfalls and all depends upon the flow of the current and the type of the river. Some of the types of waterfalls are block, cascade, tiered, horsetail, plunge and many more.

Waterfalls are usually found in mountain regions or places where the elevation is quite high such as hills, plains etc. Angel Falls in Venezuela is the world's highest waterfall at more than 3000 feet.eg dhunwadhar falls on the Narmada river.

TRANSPORT AND DEPOSITIONPROCESSES of RIVER TRANSPORTA river moves its load by :-(1) - rolling large stones and boulders.(2) - carrying sand, mud and silt in suspension.(3) - carrying minerals in solution

RIVER DEPOSITIONA river drops some of its load when either its volume or its speed decreases e.g. when it enters an arid (dry) region, crosses an area of porous rock (e.g. limestone), enters a flat or gently sloping plain or enters a lake or the sea.Material transported or deposited by a river is called alluvium.

In river meanders, the channel curves alternately right and left about the down-valley direction. Banks are steep on the outside of the bend, where erosion generally takes place, and are gently sloping on the inside where depositionnormally occurs. Sediment deposited on the inside of the bend forms a point bar. The channel also varies in cross-sectional and longitudinal form through a meander: there is usually a swallowing (riffle) at the entrance or inflexion point of the loop and a deeper part (pool) on the outside of the bend in the apex. The plan form of a meander is frequently characterized as a smooth, symmetrical loop, often as a sine-generated form.

MEANDERS

An oxbow is a crescent-shaped lake lying alongside a winding river. The oxbow lake is created over time as erosion and deposits of soil change the river's course. You can see how an oxbow lake takes shape below:

(1) On the inside of the loop, the river travels more slowly leading to deposition of silt.

(2) Meanwhile ,water on the outside edges tends to flow faster, which erodes the banks making the meander even wider.

(3) Over time the loop of the meander widens until the neck vanishes altoget-her.

(4) Then the meander is removed from the river's current and the horseShoe shaped oxbow lake is formed.

Without a current to move the water along, sediment builds up along the banks and fills in the lake.

OXBOW LAKES

A Flood Plain is a piece of land near a river that floods periodically. There are two parts to a flood plain: the floodway and the flood fringe. The floodway contains the stream channel and nearby areas through which flood flows run; the flood fringe includes areas covered by the flood without a strong current.

Flood plains are created by the phenomenon of meander erosion, which is sideways erosion affecting a riverbank. Flood waters leave sediments, rocks, and mud behind. These accumulations gradually form a flood plain.

FLOOD PLAINS AND FLOOD LEVEES

Levees are natural embankments of silt along the banks of a river, which are often several meters higher than the flood plain.

Levees can be natural or man-made. A natural levee is formed when sediment settles on the river bank, raising the level of the land around the river. The elevation along the bank increases due to the deposition of coarser material. This gives rise to hillock-like forms parallel to riverbanks. These are called flood levees.

DELTADeltas A delta is a flat area of sand and silt built into the sea. When a river enters the sea carrying large volumes of fine material, the velocity slows and causes the load to be deposited in layers .Over time, deposition material forms small islands separated by river channels called distributaries. A delta is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river. Deltas are formed from the deposition of the sediment carried by the river as the flow leaves the mouth of the river. Over long periods of time, this deposition builds the characteristic geographic pattern of a river delta..