Agents of gradation. Introduction. Gradation changes surface features of the land. It involves erosion, transportation and deposition . It involves process like degradation, aggradations and weathering. Work of river Or Running water. Introduction.
Introduction • Gradation changes surface features of the land. • It involves erosion, transportation and deposition. • It involves process like degradation, aggradations and weathering.
Work of river Or Running water
Introduction • Rivers originate from hills or mountains. • They have different amount of water In different seasons. • Some rivers water through out the year and some don’t.
They are known as perennial and non-perennial rivers. • They are the most powerful agent of gradation. • The work of the running water is also called as fluvial process.
Rivers • It consists of threestages namely - First stage Second stage Third stage
STAGE OF A RIVER FIRST SECOND THIRD
First stage • In the first stage the river has it maximum speed so most of the erosion is done in this course. It forms rapids, waterfalls, gorges, canyon, V-shaped valley and erodes it bed during the upper course. • In the upper course of a river valley the land is highest, steepest and most exposed
Waterfalls • Waterfalls occur where the bed of a river becomes suddenly steepened. • Waterfalls are caused by differences in rock hardness. • E.g.., Niagara falls, the great kaietur falls.
Niagara falls The Niagara Falls are voluminous waterfalls on the Niagara River, straddling the international border between the Canadian province of Ontario and the U.S. state of New York.
Victoria falls The Victoria Falls or Mosi-oa-Tunya(the Smoke that Thunders) is a waterfall located in southern Africa on the Zambezi River between the countries of Zambia and Zimbabwe.
Where a river derives its water from snow-melt mountains and flows through arid areas and is able to maintain its erosive power ,canyons are formed. E.g., grand canyon ,Rhine George etc. Canyons
Some valleys have very steep sides and are both narrow and deep. These are called gorges. Some valleys have very steep sides and are both narrow and deep. These are called gorges. Gorges
Interlocking spurs • An interlocking spur is a natural geographical feature which occurs in a river's upper course, where upward erosion is the dominant force in determining the river's course.
Second stage • In the middle course the river's speed becomes slow that it was in the upper course. The river deposits, erodes all the material along its way. • The main features formed by the river in its middle course are meanders, oxbow lake and flood plain.
Meanders • Meander is a loop-like bent in a river. As a river nears the sea it winds up, forming regular horseshoe shape bends, these bends are called Meanders
Flood plain is a broad flat river valley in the lower reaches of a river. A river often flows over wide plains of sediments or alluvium. This alluvium is washed down the hills and spread out over the valley floor in times of flood Flood plains
Oxbow lake is a crescent - shaped lake on a river floodplain. As the river wears away on the outside bend of the meander, the neck of the meander gets continually narrower. Ox-bow lake
Third stage • In the lower course of a river, the valley floor is extremely gently sloped. The river spreads over a large and its speed becomes very slow. Hence the river is not able to carry the sediments with it • In this course the river generally deposits and very less erosion and transportation work takes place. • The main features made by the river in its lower course are distributaries, delta and estuaries.
Distributaries • By the huge amount of deposition taking place the river channel get obstructed resulting to the formation of distributaries. The distributaries branches off from the main river take the water away from the river.
Delta • A delta is a landform that is created at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area, or another river.
Delta Arcuate delta Bird’s foot delta
Estuary • An estuary is a semi-enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea. • E.g., Klamath river
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