The wearing away or breaking down of rocks by agents present in the atmosphere like temperature, moisture and frost.The earth's surface is subject to constant changes. Both nature and humans are responsible for such changes.The extent to which a landscape  is modified depends on many factors such as internal process , external forces, nature of rocks and the length of time these processes that have been acting upon.

                                                           INTERNAL PROCESSES:

Internal processes are the processes which take place beneath the earth's surface and modify the earth's shape These include movement of tectonic plates, volcanic eruptions, and earthquakes. internal processes may produce lava plains, plateaus, rift valleys, geysers, mud pools, etc.   

External process                                                                                                                           

The external processes take place on the surface of the earth. These processes work slowly. Weather, rivers, glaciers, wind, waves etc. are some of the major agents responsible for external processes.                                                                                                                                                                   1.Weathering: The wearing away or breaking down of rocks by agents present in the atmosphere  like temperature, moisture and frost is known as weathering. weathering is considered as the phase in the gradation of  landscape, because it prepares rock materials which are transported by other agents of erosion . there are mainly three types of weathering.                                                      a)Physical weather                                                                                                     b)chemical weathering                                                                                                         c)biological weathering                                                                                                          a) Physical weathering:  it refers to mechanical disintegration of rocks without any changes in their chemical composition. Temperature and frost are the two main factors which are responsible for physical weathering.                                                                                                                                  1)Temperature: There are extreme temperature difference, the rocks break down and converted into pieces. In area of extreme range of temperature, rock surface is exposed daily to intense heating during the day and intense cooling during the night. The intensive heating expand the rocks and intense cooling contract them. As a result of the daily cycles of expansion and contraction, rocks are weakened and they break apart.                                                                                                                2)Frost:  In cooler regions, water that fills up the cracks in rocks, freezes and turn into ice which expands at night. During the day ice melts and the water seeps further into the cracks. At night the water again  freezes, widening the cracks. This continuous widening of the cracks leads to disintegration of rocks. This is called as frost action.                                                                                b)Chemical weathering: Chemical weathering changes the minerals composition of the rocks. Air and water are the main agents of chemical weathering. water is the main agent of the chemical weathering. For example, when carbon dioxide from the atmosphere or decaying matter combines with water, a weak acidic solution is produced that can dissolve calcium carbonate in the rocks and create cracks .                                                                                                                              c)Biological weathering: plants, trees, and animals also contribute to the weathering. Roots of the trees may grow into the cracks in the rocks in search of nourishment or the seeds of a tree may sprout in the soil that has collected in a cracked rocks. Burrowing animals and human beings also contribute to this process.                                                                                                                                                        Mass wasting : The gravity of earth pulls all materials downwards. This downhill movement occurring under the pull of gravity is collectively  known as mass wasting or mass movement. mass movements like landslide, mud flow ,etc. bring changes in the earth's surface..                                             At last we can say that  the changes on the  earth's surface is continuous process.Both nature and humans are responsible for such changes.                      


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