Transcript Tsunamis
Tsunamis 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. • 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. • 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 2030 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. • 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 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. • Water receding prior to a tsunami coming ashore. 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! • Photo from the boxing day tsunami 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?