tsunami

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.