The earthquakes occurring in India are due to the drifting of the Indian Plate. Scientists divide the globe into several major tectonic plates that drift very slowly. As these plates slide against each other, an immense amount of energy is released, causing heavy destruction.
Natural earthquakes caused by internal (endogenic) forces.
(i) Volcanic - Caused by volcanic eruptions, e.g. Mt Etna.
(ii) Tectonic - Caused by stress and strain along the Earth's plates or the dislodging of rocks during faulting.
(iii) Isostatic- Due to isostatic imbalance created by sudden, regional geological activity.
(iv) Plutonic - Originating deep down the earth at 250 km- 650 km of depth.
There are many fault-lines in the Earth's crust. A fault is where the blocks of crust on either side are moving relative to one another. The typical, average rate is around a millimetre per year. If this movement happened gradually, it would not pose any problems. Unfortunately, the strain builds up for decades or centuries until it becomes critical and then everything gives in at once. Once a fault gives way at one point, slip movement may occur along its whole length of hundreds of kilometres, though it is usually limited.
The strongest seismic waves are generated at the initial break-point. The closer to the break-point, the greater the energy and the greater the potential for destruction. The break-point is called the earthquake focus and the point on the surface directly above it is the epicentre. Slip further along the fault and readjustments close to the focus cause a series of smaller aftershocks, which continue for days (even years sometimes).
Scientists can't predict earthquakes but they know which regions are likely to experience them. Based on the speed and direction of the plate drift, the land masses and the tensions between different areas, accurate probabilities can be calculated. Richter is the most common scale on which the intensity of an earthquake is measured.
A volcano is a mountain or hill with an opening on the top known as a crater. Hot melted rock (magma), gases, ash and other materials from inside the Earth mix together some kilometres underground, and or erupt through the crater.
The magma is called lava when it reaches the air. Lava may be as hot as 1000 °C. Gradually the lava cools and solidifies on the earth surface, creating new landforms. In some eruptions, huge fiery clouds rise over the mountain and the rivers of lava flow down its sides.
(i) Active - Currently alive e.g. Etna, Stromboli, Pinatubo, etc.
(ii) Dormant - Not erupted for quite some time now e.g. Vesuvius, Barren Islands.
(iii) Extinct - Not erupted for several centuries / millennia or may not occur in near future, too.
The hundreds of active volcanoes on the land near the edges of the Pacific Ocean make up what is called the Ring of Fire. They mark the boundary between the plates under the Pacific Ocean and the plates under the continents around the ocean.
The Ring of Fire runs all along the west coast of South and North America, from the southern tip of Chile to Alaska. The ring also runs down the east coast of Asia, starting in the far north in Kamchatka.
Tsunami is a Japanese word meaning gaint sea-wave. A large ocean wave caused by sudden motion on the ocean floor. It could be an earthquake, a powerful volcanic eruption, or an underwater landslide. The impact of a large meteorite could also cause a tsunami. Tsunamis travel across the open ocean at great speeds and become large deadly waves in the shallow water of a shoreline. Most tsunamis are caused by earthquakes in an area where an oceanic plate is being forced down into the mantle by tectonic forces. This friction prevents a smooth flow of plates the two plates lock 'horns', causing great devastation.
The tsunamis are common in and around Japan.