Japan issued an advisory for a tsunami of 1 metre for the islands off of Izu peninsula on the eastern coast of the country. The warning followed an earthquake that had a preliminary magnitude of 6.6 that struck at 11 a.m. near Torishima island, according to the Japan Meteorological Agency. The epicentre was in the Pacific Ocean about 550 kms (340 miles) south of Tokyo. Tsunamis are giant waves caused by earthquakes or volcanic eruptions under the sea. Out in the depths of the ocean, tsunami waves do not dramatically increase in height. But as the waves travel inland, they build up to higher and higher heights as the depth of the ocean decreases.

The speed of tsunami waves depends on ocean depth rather than the distance from the source of the wave. Tsunami waves may travel as fast as jet planes over deep waters, only slowing down when reaching shallow waters. While tsunamis are often referred to as tidal waves, this name is discouraged by oceanographers because tides have little to do with these giant waves.

 
Credit: Independent News Pakistan (INP)