All about tsunamis - By Alex
Tsunamis are caused by the displacement of a large mass of water at depth or on the surface. The most frequent causes are earthquakes (about 80% of the total), then submarine or coastal landslides, volcanic eruptions, particular meteorological phenomena (so-called meteo-tsunami). More rarely, tsunami are caused by meteorite impacts.To generate a tsunami, an earthquake must occur at sea or in a coastal area. It should be superficial and strong enough to deform the ocean or sea floor. Earthquakes above magnitude 5.5 are generally considered potentially dangerous, but in reality they should exceed magnitude 6.5 - 7 to have a significant probability of generating a tsunami. A particular case is the landslides, which are widespread in the Scandinavian fjords, where waves of tens of meters are documented following the collapse of a landslide in the sea or in a lake. However, the most destructive tsunamis are those produced by large earthquakes, such as that of Sumatra in 2004 (magnitude 9.3) and Japan in 2011 (magnitude 9.1).
In the twentieth century, there were numerous devastating tsunamis of seismic origin. Just to mention the main ones, those in Alaska in 1946 and 1964, the first of which produced a tsunami that traveled for hours in the Pacific Ocean until it hit the Hawaiian Islands. At the time, there was no warning system. Another very important one is that of Chile in 1960 caused by the largest earthquake ever recorded: magnitude 9.5.