1. Tsunamis

2. What is a tsunami? A tsunami is a series of waves created when a body of water is displaced. Tsunamis can be caused by earthquakes, volcanic eruptions, landslides or asteroids at sea. Sometimes weather events such as hurricanes or cyclones (with high winds) can cause storm surges which look similar to a tsunami but are not true tsunamis.

4. Most tsunamis are caused by the movement of tectonic plates at convergent plate boundaries. Tsunamis are unlikely to occur at divergent or transform plate boundaries because water is not vertically displaced there.

5. Everyday waves in the ocean have a wavelength of about 100m. Tsunamis have a wavelength of about 200km. This means that after the tsunami wave passes a certain point, the next wave won’t arrive for 20- 30 minutes. At sea the tsunami may only be 1m high, and they go unnoticed in the open ocean. It is only when the waves go ashore that they become dangerous and devastating.

7. In the deep ocean tsunamis move at the speed of a jet aircraft (800km/h). As they approach the shore they slow down to about 70 km/h and increase in height. Tsunamis can knock down buildings, uproot trees and smash boats to pieces. http://videos.howstuffworks.com/howstuffw orks/230-how-tsunamis-work-video.htm

8. Warning signs of a tsunami There are often no warning signs. If there has been an earthquake near a body of water, a tsunami may form. Just before the tsunami comes ashore, the shoreline goes way out exposing areas that are usually underwater. There is sometimes a sucking sound as the water rushes away. At this point the only thing to do is run away, when the wave comes ashore it will travel faster than you can run.

9. Water receding prior to a tsunami coming ashore.

10. The Boxing Day Tsunami 2004 The Indian Ocean tsunami was caused by an earthquake at a convergent plate subduction zone. The earthquake measured between 9.1 and 9.3 on the Richter scale which is the strongest earthquake ever recorded on a seismograph. More than 225 000 people died in this tsunami in 11 countries Some of the waves were more than 30 m high!

11. Photo from the boxing day tsunami

13. Copy and Answer These Questions in Your Notes: TSUNAMIS 1.What is a tsunami? 2.How are tsunamis formed? 3.What is the wavelength and speed of a typical tsunami? 4.Why are tsunamis dangerous? 5.What are some indications that a tsunami may be on its way?