A tsunami is a natural disaster which is a series of fast-moving waves in the ocean caused by powerful earthquakes, volcanic eruptions, landslides, or simply an asteroid or a meteor crash inside the ocean. A tsunami has a very long wavelength. It can be hundreds of kilometers long. Usually, a tsunami starts suddenly. The waves travel at a great speed across an ocean with little energy loss. They can remove sand from beaches, destroy trees, toss and drag vehicles, houses and even destroy whole towns. Tsunamis can even be caused when a meteorite strikes the earth's surface, though it is very rare. A tsunami normally occurs in the Pacific Ocean, especially in what is called the ring of fire, but can occur in any large body of water.