Saturday, 20 February 2016

CHANGING EARTH

·        The landscape is continuously being worn away by two processes:
Weathering: 
  •  It is the breaking up of rocks on the earth’s surface. It creates rock fragments.

Erosion: 
  • As mentioned earlier, it is the wearing away of landscape by different agents like wind, water and ice.
  • The eroded material is carried away or transported by water, wind, etc. and eventually deposited.
  • Different landforms are created on the earth’s surface because of erosion and deposition.

Role of water in erosion/ deposition :

1.River :

  •  The running water of the river erodes the landscape.

2.Waterfall :

  •        A waterfall is formed when the river tumbles at steep angle:
  •      over very hard rocks or
  •      down a steep valley side

3.Ox Bow Lake :

  •       As the river enters the plain, it twists and turns forming large bends called meanders.
  •     Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer.
  •     When this happens, over a course of time, the meander loop cuts off from the river and forms a cut – off lake.
  •      Such a lake is also called an ox-bow lake


4.Floodplain :

  •      When the river overflows its banks, the neighbouring areas get flooded.
  •     When the river floods, it deposits layers of fine soil and other material called sediments along its banks.
  •     This leads to the formation of a floodplain.
  •     A floodplain is flat and fertile.

5.Levees: 
  •     The raised banks of the river (due to overflowing) are called levees.

6.Delta: 
  •     When the river approaches the sea, it becomes very slow in its flow and begins to break up into a number of streams called distributaries.
  •     The speed of the river water is so less that it starts depositing its load.
  •      Each distributary forms its own mouth.
  •      A collection of sediments from all the mouths forms a delta. 


7.Sea Waves :

  •     The erosion and deposition by water in the form of sea waves leads to the formation of coastal landforms.
  •     Some coastal landforms are as follows:

  • Sea Caves
  • Sea Arches
  • Stacks
  • Sea Cliff
  • Beaches
                           
   
           
  •     Seawaves continuously strike at the rocks. This leads to cracks. The cracks become larger and wider overtime.
  •     Thus hollow like caves are formed on the rocks. They are called sea caves.
  •     As these cavities become bigger and bigger, only the roof of the caves remains, hence forming sea arches.
  •    The erosion further breaks the roof and only the walls remain. These wall-like features are called stacks.
  •     Sea cliff is the steep rocky coast rising almost vertically above sea water.
  •     The sea waves deposit sediments along the shores forming beaches.

8. Role of ice in erosion/ deposition:


Glaciers are ‘rivers’ of ice that too erode the landscape by bulldozing soil and stones to expose the solid rock below. They create
  • Deep hollows .
  • Lakes in mountains: These are formed when the ice melts and the deep hollows get filled up with water
  • Glacial moraines: These are formed by the deposition of the material carried by the glacier such as rocks big and small, sand and silt.

9. Role of wind in erosion/ deposition :

  •     An active agent of erosion and deposition in the deserts is the wind. The landforms in the desert are

a. Mushroom Rocks: 
  •      In deserts, we can see rocks in the shape of mushrooms called mushroom rocks.
  •     The mushroom has a narrow base and a wider top.
  •     These rocks also have such a shape because the winds erode the lower section of the rock more than the upper part.

b.Sand Dunes: 
                                   
  •     When the wind blows, it lifts and transports sand from one place to another.
  •     When it stops blowing the sand falls and gets deposited in low hill – like structures called sand dunes.

c.Loess:
·        When the grains of sand are very fine and light, the wind can carry it over very long distances.
·        When such sand is deposited in large areas, it is called loess.

·         Large deposit of loess is found in China.



























No comments:

Post a Comment