Discuss the characteristics, causes and effects of Tsunami with example.

Characteristics

• Wavelength in the deep ocean is tens to hundreds of kilometres; period is minutes to an hour, so a tsunami is not a wind chop and not a single splash.
• Speed in deep water can exceed 500–800 km/h, yet the wave height offshore may be only tens of centimetres, which is why ships often do not feel it.
• Shoaling near the coast slows the wave, shortens the length, and piles the height into a wall or a rapid flood; drawdown of the sea is a lethal characteristic that pulls the curious onto the drying bed.
• Tsunamis arrive as a train: later waves can be higher than the first, and resonance in bays (as at some Japanese rias) amplifies run-up.
• They can travel trans-ocean; the 2004 waves hit Indonesia, Thailand, Sri Lanka, the Andaman–Nicobar chain, and the Tamil Nadu–Andhra coast in one morning.

Causes

• The dominant cause is a large shallow reverse-fault earthquake under the sea, as in the Sumatra–Andaman megathrust (Mw about 9.1) of 2004.
• Submarine landslides, volcanic flank collapse (Krakatau 1883), and rare extra-terrestrial impact can also displace water.
• Not every coastal quake makes a tsunami; strike-slip motion and inland epicentres usually do not, which is why public science must not treat every tremor as a wave warning.

Effects, with example

• The 2004 tsunami killed over two lakh people around the Indian Ocean; in India the Andamans, Tamil Nadu (Nagapattinam), Pondicherry, and Kerala paid in lives, boats, and salt-poisoned wells.
• Effects include drowning, debris trauma, destruction of harbours, saline soils, destroyed mangroves and coral, and long psychosocial harm; Fukushima (2011 Tohoku tsunami) added a nuclear-plant cascade as an industrial effect.
• Reconstruction can itself damage dunes that were the natural buffer.
• INCOIS runs the Indian Tsunami Early Warning System; NDMA guidelines, CRZ setbacks, mangroves, and Andaman vertical evacuation are the policy moral of 2004.