TSUNAMI

TSUNAMI

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.

Concept :

Tsunamis

• 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.