- March 21, 2021
- Posted by: OptimizeIAS Team
- Category: DPN Topics
Subject : Geography
Context : Japan’s meteorological agency lifted a tsunami advisory around an hour after a 6.9-magnitude earthquake struck off the country’s northeastern coast on Saturday, causing no immediate damage or injuries.
- These are a series of waves usually generated by movement of the sea floor. These movements are caused by different types of geophysical phenomena such as earthquakes, landslides and volcanic eruptions.
- The word tsunami is a Japanese word, represented by two characters: tsu, meaning, “harbor”, and nami meaning, “wave”.
- The tsunami waves behave very differently in deep water than in shallow water as their speed is related to the water depth.
- They frequently occur in the Pacific, where dense oceanic plates slide under the lighter continental plates. When these plates fracture they provide a vertical movement of the seafloor that allows a quick and efficient transfer of energy from the solid earth to the ocean.
Mechanism of Tsunami Waves
- Megathrust earthquakes cause a sudden displacement in a seabed sufficient to cause the sudden raising of a large body of water.
- As the subducting plate plunges beneath the less dense plate, stresses build-up, the locked zone between the plates give way abruptly, and the parts of the oceanic crust is then upthrust resulting in the displacement of a large column of water vertically.
- The tsunami on December 26, 2004, was caused after an earthquake displaced the seabed off the coast of Sumatra, Indonesia.
- A marine volcanic eruption can generate an impulsive force that displaces the water column and gives birth to a tsunami.
- During a submarine landslide, the equilibrium sea-level is altered by sediment moving along the floor of the sea. Gravitational forces then propagate a tsunami.
- Most destructive tsunamis can be caused due to the fall of extra-terrestrial objects on to the earth.