Tsunamis

Oceans 11

What is a tsunami?• Tsunamis are defined as

extremely large ocean waves triggered by underwater earthquakes, volcanic activities or landslides.

• The word tsunami was coined from the Japanese word "津波 ", translating to "harbor wave" in English.

• Tsunamis are sometimes referred to as "tidal waves" by the general public, which is a wrong as tsunamis are unrelated to the tides.

Tsunamis where?

• Tsunamis normally occur in Pacific Ocean,near deep ocean trenches

• They are relatively rare in areas surrounding the Indian subcontinent.

What causes tsunamis?

• They are caused by:

faulting (earthquakes)

volcanoes

landslides

Formation

• When a piece of the plate snaps up and sends tons of rock shooting upward with tremendous force

• The energy of that force is transferred to the water.

• The energy pushes the water upward above normal sea level. This is the birth of a tsunami.

Formation

• After the energy pushes the water upwards, gravity acts upon it, spreading the energy out horizontally.

• Watch what happens!

http://science.howstuffworks.com/tsunami3.htm

Speed• The tremendous force created by the seismic disturbance

generates the tsunami's incredible speed. The actual speed of the tsunami is calculated by measuring the water depth at a point in time when the tsunami passes by.

• A tsunami's ability to maintain speed is directly influenced by the depth of the water. A tsunami moves faster in deeper water and slower in shallower water.

• So unlike a normal wave, the driving energy of a tsunami moves through the water as opposed to on top of it. As a result, as a tsunami moves though deep water at hundreds of miles an hour, it is barely noticeable above the waterline. A tsunami is typically no more than 3 feet (1 meter) high until it gets close to shore.

Hitting Land

• When a tsunami reaches land, it hits shallower water. The shallow water and coastal land acts to compress the energy traveling through the water. This starts the transformation of the tsunami.

Hitting Land• The topography of the seafloor and

shape of the shore begins to affect the tsunami's appearance and behavior.

• Also, as the velocity of the wave diminishes, the wave height increases considerably -- the compressed energy forces the water upward.

• A typical tsunami approaching land will slow down to speeds around 30 miles per hour (50 kph), and the wave heights can reach up to 90 feet (30 meters) above sea level.

• As the wave heights increase during this process, the wave lengths shorten considerably. (Think of squeezing an accordion.)

Hitting Land

• A witness on the beach will see a noticeable rise and fall of beach water when a tsunami is imminent.

• Sometimes, the coastal water will disappear completely as it is drawn into the tsunami.

• This amazing event is followed by the actual trough of the tsunami reaching shore.

• Tsunamis most often arrive as a series of strong and fast floods of water, not one single, enormous wave.

Tsunami video

• http://videos.howstuffworks.com/Tsunami_101-video.htm

Indian Ocean Tsunami26th December 2004

The USGS (United States Geological Survey) record of the earthquake

Two tectonic plates, the Australian and Eurasian plates, meet just off Sumatra's south-west coast, grinding together and sending periodic seismic tremors through the region. At 0059 GMT a violent rupture occurred on the sea floor along a fault about 1,000km long.

Area affected The 9.0 magnitude quake, which was the strongest in the world for at least 40 years, wreaked havoc across the whole region.

Walls of water, tens of metres high, slammed into coastal resorts thousands of miles apart. Surging seas and floods were reported as far away as east Africa.

The killer wave strikes Kalutara Sri Lanka

Low lying coastal areas were left obliterated and

flooded as here in Aceh province in

Sumatra, Indonesia

Reports indicate that the north and west coasts of Sumatra

experienced the worst destruction

Whole villages were flattened as here in Sri Lanka

“Scale of devastation Thousands are reported to have been killed, but there has been little news from the worst-hit areas where all transport and communication links were destroyed. “ bbc.co.uk 27.12.04

The Aftermath

Millions of people were left homeless

Cuddalore, south of Madras, India

Penang, Malaysia

All that remains of luxury holiday accommodation on Phi

Phi Island, Thailand