|MLA Citation:||Bloomfield, Louis A. "Question 532"|
How Everything Works 16 Jan 2018. 16 Jan 2018 <http://howeverythingworks.org/print1.php?QNum=532>.
The wavelength of a tsunami is enormous—hundreds or even thousands of meters. As a result, a tsunami travels hundreds of kilometers per hour and extends downward deep into the ocean. Because it disturbs so much water, it carries a great deal of energy and it delivers this energy to the shore when it hits. Tsunamis are normally created by earthquakes or volcanic eruptions that sudden shift the supporting surfaces of a large amount of water. The water experiences a sudden impulse when the land or seabed shifts and a wave is emitted. You can launch a similar wave simply by shaking the end of a basin of water. But when a large region of land or seabed moves, the wave that's launched has a very long wavelength and tremendous energy. This tsunami heads off with enormous speed until it encounters the gradual shallowing of a seashore. There it becomes deformed because the lack of water in front of it causes its crest to become incomplete. Eventually the tsunami breaks in churning surf. The height of this breaking wave crest and the distance it travels onto shore before it stops depends on the total energy of the tsunami, but heights of 10 or 20 meters are not uncommon. Such waves can travel hundreds of meters up a beach or oceanfront if the slope is sufficiently gradual.