1. Waves Oceans 11

2. What causes waves? winds cause waves on the surface of the ocean (and on lakes). winds cause waves on the surface of the ocean (and on lakes). The wind transfers some of its energy to the water, through friction between the air molecules and the water molecules. The wind transfers some of its energy to the water, through friction between the air molecules and the water molecules. Stronger winds (like storm surges) cause larger waves. Stronger winds (like storm surges) cause larger waves.

3. How do waves move? Waves of water do not move horizontally, they only move up and down (a wave does not represent a flow of water). Waves of water do not move horizontally, they only move up and down (a wave does not represent a flow of water). This is demonstrated by watching a floating buoy bob up and down with a wave; it does not, however, move horizontally with the wave. This is demonstrated by watching a floating buoy bob up and down with a wave; it does not, however, move horizontally with the wave.

4. Tsunamis Tsunamis (sometimes called tidal waves) are different from surface waves; they are usually caused by underwater earthquakes, volcanic eruptions, or landslides. Tsunamis (sometimes called tidal waves) are different from surface waves; they are usually caused by underwater earthquakes, volcanic eruptions, or landslides. Tsunamis

5. Causes of Tsunamis 1. underwater earthquakes 2. a volcanic eruption, volcanic eruptionvolcanic eruption 3. a sub-marine rockslide, or, more rarely, by 4. an asteroid or meteoroid crashing into in the water from space. (rare occurrence) asteroidmeteoroidasteroidmeteoroid

6. Tsunamis cont…. 1. Most tsunamis are caused by underwater earthquakes, but not all underwater earthquakes cause tsunamis - an earthquake has to be over about magnitude 6.75 on the Richter scale for it to cause a tsunami. Richter scale Richter scale 2. About 90 percent of all tsunamis occur in the Pacific Ocean.

7. The word Tsunami The word tsunami comes from the Japanese word meaning "harbor wave." The word tsunami comes from the Japanese word meaning "harbor wave."Japanese Tsunamis are sometimes incorrectly called "tidal waves" -- tsunamis are not caused by the tides (tides are caused by the gravitational force of the moon on the sea). Tsunamis are sometimes incorrectly called "tidal waves" -- tsunamis are not caused by the tides (tides are caused by the gravitational force of the moon on the sea).tides Regular waves are caused by the wind. Regular waves are caused by the wind.

8. The Development of a Tsunami: A tsunami starts when a huge volume of water is quickly shifted. A tsunami starts when a huge volume of water is quickly shifted. This rapid movement can happen as the result of an underwater earthquake (subduction – one plate sliding under another) This rapid movement can happen as the result of an underwater earthquake (subduction – one plate sliding under another)

10. The Size of a Tsunami: Tsunamis have an extremely long wavelength, hundreds of meters (wavelength = distance between the crest (top) of one wave and the crest of the next wave) Tsunamis have an extremely long wavelength, hundreds of meters (wavelength = distance between the crest (top) of one wave and the crest of the next wave) In the deep sea, a tsunami's height can be only about 1 m In the deep sea, a tsunami's height can be only about 1 m

11. Speed of Tsunami A tsunami can travel at well over 970 kph (as fast as a jet!!!) A tsunami can travel at well over 970 kph (as fast as a jet!!!) Regular wave = 90 km/hr (caused by wind) Regular wave = 90 km/hr (caused by wind) A tsunami wave can travel across the entire ocean in a few hours!! A tsunami wave can travel across the entire ocean in a few hours!!

13. When the Tsunami hits the coast As a tsunami wave approaches the coast (where the sea becomes shallow), the trough (bottom) of a wave hits the beach floor, causing the wave to slow down, to increase in height and to decrease in wavelength. As a tsunami wave approaches the coast (where the sea becomes shallow), the trough (bottom) of a wave hits the beach floor, causing the wave to slow down, to increase in height and to decrease in wavelength.