The lithosphere is broken into a number of plates known as the Lithospheric plates. These plates move just a few millimeters each year. This is because of the movement of the molten magma inside the earth. It moves in a circular manner inside the earth.
The earth movements are divided on the basis of the forces cause them. The forces act in the interior of the earth are called as Endogenic forces and the forces that work on the surface of the earth are called as Exogenic forces.
Endogenic forces sometimes produce sudden movements and at the other times produce slow movements.
A volcano is a vent (opening) in the earth’s crust through which molten material erupts suddenly. When the Lithospheric plates move, the surface of the earth vibrates. The vibrations can travel all-round the earth. These vibrations are called earthquakes. The place in the crust where the movement starts is called the focus. The place on the surface above the focus is called the epicenter. Vibrations travel outwards from the epicenter as waves. Greatest damage is usually closed to the epicenter and the strength of the earthquake decreases away from the center.
Earthquakes cannot be predicted but some common earthquake prediction methods adopted locally by people include studying animal behavior: fish in the ponds get agitated, snakes come to the surface.
The landscape is being continuously worn away by two processes – weathering and erosion. Weathering is the breaking up of the rocks on the earth’s surface. Erosion is the wearing away of the landscape by different agents like water, wind and ice.
The running water in the river erodes the landscape. As the river enters the plain it twists and turns forming large bends known as meanders.
Due to continuous erosion and deposition along the sides of the meander, the ends of the meander loop come closer and closer. In due course of time the meander loop cuts off from the river and forms a cut-off lake, also called an ox bow lake. As it floods, it deposits sediments along its banks and forms a flat fertile floodplain. The raised banks are called levees.
As the river approaches the sea, the speed of the flowing water decreases and it begins to break up into a number of streams called distributaries. The collection of sediments from all the mouths of distributaries forms a delta.
Sea waves continuously strike at the rocks. Cracks develop and over time they become larger and wider. 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, thus forming sea arches. Further, erosion is left. These wall-like features are called stacks. The steep rocky coast rising almost vertically above sea water is called sea cliff. The sea waves deposit sediments along the shores forming beaches.
Glaciers erode the landscape by bulldozing soil and stones to expose the solid rock below and carved out deep hollows there. As the ice melts they get filled up with water and become beautiful lakes in the mountains. The material carried by the glacier such as rocks big and small; sand and silt get deposited. These deposits form glacial moraines.
In deserts rocks in the shape of a mushroom, are called mushroom rocks. Winds erode the lower section of the rock more than the upper part. Therefore, such rocks have narrower base and wider top. 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. There are called sand dunes. 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 deposits of loess is found in China.