What is TSUNAMI?
Tsunamis are huge waves caused by earthquakes or volcanic eruptions under the ocean. Out in the depths of the ocean, tsunami waves do not significantly increase in height. But as the waves travel inland, they develop to higher and higher heights as the depth of the ocean decreases. The speed of tsunami waves depends on ocean depth instead of the distance from the source of the wave. Although tsunami wave speed is almost similar to jet planes over deep waters, it only slows down when it reaches shallow waters. The name is discouraged by oceanographers because tides have little to do with these giant waves while tsunamis are often referred to as tidal waves.
Causes
Generally, the cause for tsunami is sudden motion on the ocean floor. The sudden motions are an earthquake, a powerful volcanic eruption, or an underwater landslide. Another cause can be the influence of a huge meteorite. Tsunami waves travel the open sea at extraordinary speed and incorporate with in the shallow water of a shoreline. Most wages are caused by earthquakes created in a subduction zone, a zone where a sea plate is being constrained down into the mantle by plate tectonic forces.
A. Earthquake – Significant loss of life and environmental destruction resulted from the 2011 Japan tsunami that was caused by a magnitude 9.0 (on the 10-pt Richter scale) earthquake 70 km off the coast of eastern Japan. The waves it generated reached as high as 40 m and traveled as much as 10 km inland.
B. Volcanic eruption – The eruption of Krakatoa in Indonesia in 1883 created a tsunami that killed over
120,000 people.
C. Landslide – A giant landslide produced a massive tsunami in Lituya Bay, Alaska, in 1958. Eyewitness
accounts say the tsunami was about 30 m high, it ran up the sides of the bay to heights of over 520 m.
Similarly, a tsunami can be produced when parts of a glacier break off into the water.
Types of Tsunami
Local Tsunami
Regional Tsunami
Distant Tsunami
Local Tsunami Is destructive tsunami that is usually generated by an earthquake.
The time between the underwater event and the arrival of the tsunami at the shore can be under an hour and sometimes less than 10 minutes.
A regional tsunami is one that causes damage from 100 km to 1000 km from the underwater event that causes the tsunami. Regional tsunamis can take between 1-3 hours to reach and affect the shoreline providing slightly more warning time than local tsunamis.
Distant Tsunami, also called tale-tsunami or ocean-wide tsunami is originating from more than 1,000 km away from the landfall. It takes more than three hours to arrive. It causes additional casualties and destruction on far away shores traveling across the entire ocean basin with sufficient energy.