Tsunami is commonly referred to as a sea monster. It cuts across the sea with an awesome speed. On reaching land, it sucks most of the water out of the harbor; then, the creature may rise more than 100 feet tall and flatten whole villages. Often before a tsunami hits, there is a giant vacuum effect, and water is sucked from harbors and beaches. People see the bare sea bottom littered with flopping fish and stranded boats. This is because waves are made out of crests, or high points, and troughs, or dips between crests, and when a trough hits land first, the water level drops drastically. Usually another wave blasts ashore after 15 minutes, to be followed by succeeding waves, for two hours or more.Tsunami, a most destructive waves and often wrongly called tidal waves, is not caused by tides or even by the wind, but by underwater earthquakes, landslides or volcanic eruptions. These disturbances cause the seabed to move rapidly, and shift a large amount of water, disrupts the sea surface. A train of waves is set in motion traveling away from the source of disturbance.Some tsunami many reach heights of 100 feet or more and can race across the ocean at 500 miles an hour. Oddly, in deep water, the waves are only a few feet high but upon approaching shore, this increase in energy and height.