Our Changing Earth
When the lithosphere is broken into a number of plates is called the Lithospheric plates. The plates are moving because they are floating on the molten magma inside the earth. The movement of lithospheric plates causes changes on the surface of the earth. There are two types of the earth movements which are divided on the basis of the forces- endogenous forces and exogenous forces. Endogenic forces are those forces which act in the interior of the earth. Exogenic forces that work on the surface of the earth. These movements like volcano and earth quakes cause mass destruction over the surface of the earth. A volcano is a vent (opening) in the earth’s crust through which molten material erupts suddenly.
Origin of an Earthquake
Earth quakes are the vibration of the earth’s surface caused by the movements of lithospheric plates. There are three types of earthquake waves: P waves or longitudinal waves; S waves or transverse waves; L waves or surface waves. The place in the crust where the movement starts is called the focus. The place on the surface above the focus is called the epicentre. Vibrations travel outwards from the epicentre as waves. Greatest damage is usually closest to the epicentre and the strength of the earthquake decreases away from the centre.
Formation of landscape
Weathering and erosion are two processes through which landscape is being continuously worn away. 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 eroded material is carried away or transported by water, wind, etc. and eventually deposited to form different landforms on the surface of the earth. The factors that influence the formation of landscape are discussed below:
1. Work of a River
When the river tumbles at steep angle over very hard rocks or down a steep valley side it forms a waterfall. Meander is a large bends formed by twisting and turning of the river while entering the plain. An ox-bow lake is a cut-off lake formed due to cut off of a meander loop. Floodplain is formed by the deposition of fine soil and other materials through floods. Levees are the raised banks of the rivers. Distributaries are the streams which distribute the rivers waters into different stream. Deltas are formed by the deposition of sediment carried by a river as the flow leaves its mouth.
2. Work of Sea Waves
The Coastal landforms are formed by the erosion and deposition of the sea waves. Sea caves are hollow like’s caves formed by the continuous striking of sea waves at the rocks. Sea arches are hallowing likes caves which are formed on the caves remain. The roof of sea arches breaks by erosion and only walls are left. These walls 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.
3. Work of Ice
Glaciers are “rivers of ice” which too erode the landscape by bulldozing soil and stones to expose the solid rock below. The material carried by the glacier such as rocks big and small, sand and silt gets deposited. These deposits form glacial moraines.
4. Work of wind
Wind is an active agent of erosion and deposition in the deserts. Mushroom rocks are found in deserts in the shape of a mushroom. Sand dunes are those hills like structures which are formed by the deposition of blowing wind in deserts. Loess is formed when deposition of sand grains (i.e. fine and light) by the wind over very long distances.