To understand what a tsunami is and what causes them to form.
To learn about the destructive effects of a tsunami.
To appreciate what responses humans have to tsunamis including methods to try and reduce the destructive effects of tsunamis.
To look at a case study of tsunami.
Revision guide page 11
NT pages 32-33
Need w/s sequence of a tsunami
This is a painting from the 19 th Century… Why do you think someone has drawn this painting? Where in the world do you think the artist is from? What is being shown in this picture? What emotions does the painting convey to the viewer?
A tsunami is a special type of wave where the entire depth of the sea or ocean is set in motion by an event. Earthquakes, mass movements above or below water, some volcanic eruptions and other underwater explosions, landslides and underwater earthquakes all have the potential to generate a tsunami. The event displaces the water above it and creates a huge wave. Due to the immense volumes of water and energy involved, the effects of tsunami can be devastating. A tsunami is a very destructive secondary effect of a earthquake. The wave can travel at speeds over 500mph. The following link shows how tsunamis are formed… http://videos.howstuffworks.com/howstuffworks/230-how-tsunamis-work-video.htm Animated guide: Tsunamis
A Tsunami develops as follows:
A normal wind-driven wave may have a length of 100m from crest to crest, but a tsunami may be 200km in length
A further feature of tsunamis is their relatively small wave height on the open sea. A notmal wave has a height of 2m but a tsunami wave has a height between half a metre and one meter.
Even though they can travel up to 1000 km/h , these waves are generally not noticeable in deep waters. The wave itself only becomes dangerous once it reaches land.
In coastal areas where water levels gradually become shallower, the wave will slow down, reduce in length and gain in height - tower into a wave wall as much as 30 meters high.
The reason for this is the mass of water and energy contained in the tsunami wave.
Whereas only the upper water layers are being moved in wind created waves , with a Tsunami wave, an entire mass of water from the sea bed to the surface is in motion .
If a trough of a tsunami wave approaches the land first, the water will be pulled back into the sea by enormous currents . Vast stretches of the seabed are often drained as happened during the December 2004 tsunami. In this case, and if recognised, people on the beach and beachfronts have between a few minutes and half an hour to escape to higher ground. The time to escape depends on when the wave crest strikes.
The first wave, that can grow to be up to 30 meters high at the beach, will usually be followed by more waves that are sometimes even more dangerous.
Not only the crests of waves are dangerous but also the troughs, since their currents can pull people and whole houses many miles into the sea.
How do Tsunamis develop?
Write a definition of ‘tsunami’
Cut and paste the diagrams to show the sequence of a tsunami. Annotate the diagrams as appropriate.
Why does the wave get higher when it approaches land?
An undersea earthquake is the most common cause of a tsunami but what other causes are there?
Why does the sea get sucked out away from the beach just before the tsunami hits the shore?
Tsunami mechanisms - earthquake
Now watch the moviemaker about the Boxing Day tsunami and start to complete the information on the A3 worksheet.
Now read p130 Geog1 and the ‘Tsunami information sheet’ and complete the information on the worksheet.
You will need to find a photo of the effects and annotate it as part of your homework!
Create a timeline of the events of the 12 hours following the earthquake off the coast of Indonesia – use the map on p130 Geog1 to help you.