IAS Exam Preparation of Geography Section via Infographics
You will be tested by UPSC on Questions relating to Geomorphology. Earthquakes and Tsunamis are an important component of Geomorphology.
Geography for IAS Exam Preparation 2016
Topic – Earthquakes and Tsunamis
- Earthquake is a vicious tremor, rolling or hasty shock on surface of earth’s crust, sending out a sequence of shock waves in all directions from its place of source which is known as epicentre.
- Earthquake is considered as most dangerous natural disasters causing massive destruction and causality to human life and debilitating impact on societies.
- An earthquake’s power is measured on the Richter scale using an instrument called a ‘seismometer’. A seismometer detects the vibrations caused by an earthquake. It plots these vibrations on a seismograph.
Most earthquakes are causally related to compressional or tensional stresses built up at the margins of the huge moving lithospheric plates that make up the earth’s surface. The immediate cause of most shallow earthquakes is the sudden release of stress along a fault or fracture in the earth’s crust, resulting in movement of the opposing blocks of rock past one another.
These movements cause vibrations to pass through and around the earth in wave form, just as ripples are generated when a pebble is dropped into water. Volcanic eruptions, rockfalls, landslides, and explosions can also cause a quake, but most of these are of only local extent. Shock waves from a powerful earthquake can trigger smaller earthquakes in a distant location hundreds of miles away if the geologic conditions are favorable.
Two tectonic plates meet beneath the Himalayas along a fault line. The India plate is moving north at around 45 mm a year and pushing under the Eurasian plate. Over time that is how the Himalayas were created. catastrophic earthquake in Nepal occurred because of two converging tectonic plates: the India plate and the overriding Eurasia plate to the north.
Tectonic plates are the large, thin, relatively rigid plates that move relative to one another on the outer surface of the Earth. Plates are always slowly moving, but they get stuck at their edges due to friction. When the stress on the edge overcomes the friction, there is an earthquake that releases energy in waves that travel through the Earth’s crust and cause the shaking that we feel.
Plate tectonics is the theory that the outer rigid layer of the earth (the lithosphere) is divided into a couple of dozen “plates” that move around across the earth’s surface relative to each other.
In essence, plate-tectonic theory is elegantly simple. Earth’s surface layer, from 50 to 100 km (30 to 60 miles) thick, is rigid and is composed of a set of large and small plates. Together these plates constitute the lithosphere. The lithosphere rests on and slides over an underlying weaker (but generally denser) layer of plastic partially molten rock known as the Asthenosphere.
Plate movement is possible because the lithosphere-asthenosphere boundary is a zone of detachment. As the lithospheric plates move across Earth’s surface, driven by forces as yet not fully understood, they interact along their boundaries, diverging, converging, or slipping past each other. While the interiors of the plates are presumed to remain essentially under formed, plate boundaries are the sites of many of the principal processes that shape the terrestrial surface, including earthquakes, volcanoes and orogeny (that is, formation of mountain ranges).
- Tsunami is devastating natural disaster and immensely affects the economic and living conditions of region where it hits. Tsunami is a Japanese phrase which means tsu means harbour and nami means wave.
- This geophysical phenomenon is associated with earthquake or volcanic eruption or landslides or adjacent to oceans and results in unexpected movement of water column.
- The channel of tsunami involves the movement of water from surface to seafloor which indicates it is directly linked to depth of water bodies that is deeper the ocean, higher is the movement of water.
- Consequently, as wave approaches land and reaches increasingly shallow water, it gets slow down. However, the water column still in deeper water is moving slightly faster and catches upward, resulting into wave gathering up and becoming much higher.
Most tsunami are caused by large earthquakes on the sea floor when slabs of rock move past each other suddenly, causing the overlying water to move. The resulting waves move away from the source of the earthquake event. Underwater landslides can cause tsunami as can terrestrial land which slumps into the ocean.
Less common are tsunami initiated by volcanic eruptions. These occur in several ways:
- destructive collapse of coastal, island and underwater volcanoes which result in massive landslides
- pyroclastic flows, which are dense mixtures of hot blocks, pumice, ash and gas, plunging down volcanic slopes into the ocean and pushing water outwards
- a caldera volcano collapsing after an eruption causing overlying water to drop suddenly.
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