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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.

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Oceans 11

What is a tsunami

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 where?

  • Tsunamis normally occur in Pacific Ocean,

    near deep ocean trenches

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

What causes tsunamis

What causes tsunamis?

  • They are caused by:

    faulting (earthquakes)





  • 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.



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

  • Watch what happens!




  • 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

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 land1

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 land2

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

Tsunami video

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

Indian ocean tsunami

Indian Ocean Tsunami

26th 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


The Aftermath

“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


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

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