Tsunami- Properties of Tsunami Wave
What causes a Tsunami? What are the properties of a Tsunami wave?
Introduction: (upto 30 words) Briefly explain Tsunami
Body: (upto 100 words) Elaborate on the various causes of Tsunami and also the properties of a Tsunami wave.
Conclusion: (upto 30 words) Mention the importance of taking precautionary measures in India.
Tsunami is a Japanese word for “Harbour wave”. They are also known as seismic sea waves.
- They are very long-wavelength water waves in oceans or seas. They are commonly referred to as tidal waves because of long wavelengths, although the attractions of the Moon and Sun play no role in their formation.
- They sometimes come ashore to great heights – tens of metres above mean tide level – and may be extremely destructive.
What causes Tsunami?
A tsunami can be caused by any disturbance that displaces a large water mass from its equilibrium position/ The usual immediate cause of a tsunami is sudden displacement in a seabed due to submarine earthquakes sufficient to cause the sudden raising or lowering of a large body of water.
- Earthquakes: 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.
- Landslides: Landslides can happen on the seafloor, just like on land. Areas of the seafloor that are steep and loaded with sediment, such as the edge of the continental slope, are more prone to undersea landslides. When an undersea landslide occurs (perhaps after a nearby earthquake) a large mass of sand, mud and gravel can move down the slope. This movement will draw the water down and may cause a tsunami that will travel across the ocean.
- Volcanic eruptions: Tsunami initiated by volcanic eruptions are less common. 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. Also, destructive collapse of coastal, island and underwater volcanoes which result in massive landslides.
- Meteorological: Some meteorological conditions, especially rapid changes in barometric pressure, as seen with the passing of a front, can displace bodies of water enough to cause trains of waves with wavelengths comparable to seismic tsunamis, but usually with lower energies. These are essentially dynamically equivalent to seismic tsunamis, the only differences being that meteotsunamis lack the transoceanic reach of significant seismic tsunamis and that the force that displaces the water is sustained over some length of time such that meteotsunamis cannot be modelled as having been caused instantaneously.
- Man-made reasons: There have been studies of the potential of the induction of and at least one actual attempt to create tsunami waves as a tectonic weapon. In World War II, the New Zealand Military Forces initiated Project Seal, which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park; the attempt failed.
Properties of Tsunami Waves:
- Tsunamis are a series of waves of very, very long wavelengths and period created in oceans by an impulsive disturbance.
- Tsunamis are different from the wind-generated waves which usually have a period of five to twenty seconds.
- Tsunamis behave as shallow-water waves because of their long wavelengths. They have a period in the range of ten minutes to two hours and a wavelength exceeding 500 km.
- The rate of energy loss of a wave is inversely related to its wavelength. So tsunamis lose little energy as they propagate because of their very large wavelength.
- So they will travel at high speeds in deep waters and travel great distances as well losing little energy. A tsunami that occurs 1000 metres deep in water has a speed of 356 km per hour. At 6000 m, it travels at 873 km per hour.
- It travels at different speeds in water: it travels slow in water that is shallow and fast in deep water.