2. Rivers

In the previous grade, i.e. grade 6, we have learnt that the earth's surface is highly uneven, ranging from mountain and highlands to valley, plains and trenches. In the same chapter, we also studied about various orders of landforms and how landforms are classified, formation of continents, oceans and continents. In this chapter, let's see landforms of rivers, glaciers etc.

Source: where the stream begins or the place of origin of river.

  

Mouth: The end of the river where the river joins a lake, sea, ocean or a large waterbody.

 

  

  

‘V’ shaped valley: This is a long trough in the landscape that has been formed due to erosion of the river. V-shaped valleys are usually found in the mountains and hills.

 

 

Tributary: A stream or river that flows into a larger watercourse or main river.

  

Waterfall: Falling of river water in the steep vertical step in the course of the river. It is formed when the soft rocks are removed by erosion. E.g. Coutrallam falls, and Thirparappu falls in Tamilnadu.

 

  

  

Plunge pool: Hollow feature at the foot of a small waterfall in a river. The pool is formed because the water plunging into it has eroded the river bed.

 

  

Alluvial fan: A triangle-shaped deposit of gravel, sand, and even smaller pieces of sediment, such as silt. It occurs when the river enters a plain or the foot-hills.

  

Meanders: Meander is a bend in the course of a river, formed when the river enters the plain. Here both erosion and deposition take place simultaneously, i.e. an outer stream of the river erodes the outer banks and widens its valley, whereas the inner part of the river has less energy and deposits silt. E.g. Meanders along the River Vellar near Sethiyathope in Cuddalore District, Tamil Nadu.

 

  

  

Oxbow lake: When a meander is sealed off as a result of continuous erosion and deposition, a small arc-shaped lake forms called an oxbow lake.

  

Sediment: When river floods, material that has been carried by rivers and then deposited on its banks is called sediment. Sediment may be called alluvium if it deposited on the bed of a river.

  

Flood plain: It is a flat land of the river valley close to the river banks and is usually found in the lower course of a river. It is a fertile area of land used for agriculture and growing crops.

 

 

Levee: Levee is a natural or artificially raised banks that block water from going where it is not intended to.

 

 

Distributary: A distributary is a river that branches off from the main river to merge into the sea. A distributary is the opposite of a tributary. Distributaries are a common feature at the deltas, i.e. when the river approaches the sea.

  

Delta: When a river approaches the sea, the velocity of the river becomes remarkably slow that it begins to deposit its load. Each distributary forms its own mouth. This results in the formation of a fan-shaped area of sediment built up at the mouth of a river with the collection of sediments from all the mouths to form the Delta. Deltas are highly productive and populated lands. With its abundant minerals, it favours cultivation.