The word tsunami is a Japanese word which means “Tsu” to the harbor and “NAMI” to wave: “harbor wave”. A tsunami sounds like a freight train. Tsunamis are caused by undersea earthquakes that lead to the displacement of a large volume of a body of water. These are a series of giant ocean waves that can move thousands of miles across the sea with tremendous force and energy. They have massive destructive power. They can be generated by volcanic eruptions, earthquakes, underwater landslides, large meteorite impacts, etc. They move at speeds between 500 and 800kph and can go up to 10 to 15 m in height. Tsunamis can have wavelengths ranging from 10 to 500 km and wave periods of up to an hour.
The earth is made up of pieces of hard rock fitted together like a jigsaw. These are called tectonic plates. They move very slowly. Tsunamis are typically caused by undersea earthquakes at tectonic plate boundaries. Oceanic plates are denser/heavier than continental plates and so they slide under the continental plates. The place where this occurs is known as a subduction zone. As a tsunami leaves the deep water of the open-ocean and travels into the shallower water near the coast, it changes. As the water depth decreases, the tsunami slows. As the tsunami’s speed reduces, its height grows. This is called shoaling. Because of this shoaling effect, a tsunami that is unnoticeable at sea may grow to be several meters in height near the coast. Tsunami reaches the coast with tremendous amounts of energy and destroys whatever comes in its way. Chile, Nicaragua, Mexico, and Indonesia lies in this subduction zone and are prone to earthquakes. Nearly 80% of tsunamis occur in the Pacific Ocean’s “Ring of Fire,” where tectonic shifts lead to earthquakes and volcanoes.
The effect of the tsunami can be reduced by building tsunami walls in the coastal areas. Floodgates and channels can be built to redirect the water from the tsunami. The measures can slow down the effect of the tsunami.
Scientists can accurately estimate the time when a tsunami will arrive almost anywhere around the world based on calculations using the depth of the water, distances from one place to another and the time that the earthquake occurred.
The Pacific Marine Environmental Laboratory developed the instrument, known as TSUNAMETER for detecting tsunamis and quickly alerting scientists when a tsunami occurs. It measures changes in water pressure when a tsunami passes above.
A tsunami can be detected by tidal gauges. Tide gauges measure the height of the sea-surface and are used for measuring tide levels. These consist of a sensor that is connected to a vertical tube that opens at the lower end in the water. Water enters the device by the bottom pipe, and electronic sensors measure its height and record it to a tiny computer. Most of the tide gauges operated by the Bureau of Meteorology’s National Tidal Centre are SEAFRAME stations (Sea Level Fine Resolution Acoustic Measuring Equipment).
The National Oceanic and Atmospheric Administration (NOAA) have developed the Deep-ocean Assessment and Reporting of Tsunamis (DART) System whose ranges of stations are installed in the Pacific Ocean. These provide information regarding tsunamis while they are far away. It consists of a seafloor bottom pressure recording (BPR) capable of detecting tsunamis and is connected to surface buoy via sonar to the Pacific Tsunami Warning Center (PTWC).
Japan experienced the worst ever earthquake disaster on Friday 11th March 2011 leading to massive destruction with blackouts, fire, and tsunami. The magnitude of the earthquake was 8.9 that hit Japan’s northeastern coast.