Tsunami

[Michiko]

A series of waves in a body of water (ocean, sea, lake, etc) that wreaks havoc on the coastlines of said body of water. Caused by displacement of the water, like throwing a rock into a pond; mostly caused by earthquakes, landslides, volcanic eruptions, the occasional asteroid/comet, anything that disrupts the water.
Unlike ordinary waves, tsunami waves act more like shock waves from an explosion; they affect the whole water column from the surface to the sea floor and in the open sea travel as fast as an [airliner]. [In deep water], they hardly look different from normal waves, but as they approach the shore they slow down, their energy is compressed, and they turn into monsters: the water often drains from the beach, exposing the sea floor and [stranding] boats and [sea animals] (people should know that this is a warning to run like hell for [high ground]); then the first of a series of increasingly huge waves batter the coastline and sweep people inland, one wave coming in just as the previous one is draining away; finally, the waves drain back to sea, dragging debris and people with them and leaving the coast a mass of wreckage.

[Sonia]

A long, high sea wave caused by an earthquake or other disturbance.

[Renato]

an extremely large wave caused by a violent movement of the earth under the sea