Tsunamis

Learning Objectives:

- To develop your understanding of the term Tsunami.

- To be able to identify the reason a tsunami occurs and its affects.

The Origin of the Word

• The word “Tsunami” comes from the Japanese word ‘tsu’ (meaning harbour) and ‘nami’ (meaning wave).

• Tsunamis are common throughout Japanese history, with 195 documented events.

Tsunami: A series of waves created when a body of water (ex. Ocean) is rapidly displaced from events such as, underwater earthquakes, volcanic action, nuclear testing, landslides or even asteroid impacts.

HOW A TSUNAMI IS CREATED

Tectonic plates convergeon plate boundaries, forcing

one plate upwards.This causes an Earthquake,

and displaces LARGE amounts of water.

The displaced water then moves away from the Earthquake epicentre, creating a large wave that forms a tsunami

Other Ways a Tsunami is Formed

If an asteroid hits an ocean, it could

cause a large Tsunami.

Underwater volcanoeruption can cause a

A tsunami

A landslide that deposits large

amounts of rock into a body

of water could cause a tsunami

What warning signs are there to tell a person a tsunami is going to hit the coastline?

Tsunamis are difficult to detect out in the ocean. The only warnings signs are, if you can feel an earthquake or if you

see the draw back of the shoreline.

Why are Tsunamis difficult to detect out in the Ocean?

THE BUILD UP OF THE WAVE:

1) Large amounts of water is displaced

2) The water moves away from point of origin

3) Initially the wave HEIGHT is SMALL, with a LARGE wave LENGTH

4) As the wave reaches a coast, the DRAWBACK slows the front of the wave, causing the back to catch up.

5) This condenses the wave length and INCREASES the wave height dramatically.

How do coastlines affect the height of the tsunami

The height of a tsunami is partially dependent on the coastline. If the coast has a gradual drop-off in the water, the wave height will not be forced to build up in height dramatically, keeping a larger wave length.

If the coastline has a steep drop-off into the water, then the wave’s height increases drastically. This is due to the water under the wave being forced upward as it hits the shore

This image is of a tsunami the struck Thailand on 26th Dec. 2004.

The Indian Ocean Tsunami

This undersea mega thrust ___________ struck at 00:58:53 UTC (07:58:53 local time) in the Indian Ocean off the western coast of northern Sumatra, __________. It was the largest earthquake on Earth since ______, and tied for _______ largest since 1900. This earthquake cause a giant Tsunami, that took over 200, 000 lives in __________ countries.

earthquakeIndonesia 1964 fourtheleven

Epicentre of the earthquake

The progress of the wave across the ocean

How BIG?

The earthquake was unusually large in geographical extent. An estimated 1,200 km (750 mi) of fault line slipped 20 m (60 ft) along the subduction zone where the India Plate dives under the Burma Plate. The seabed of the Burma plate is estimated to have risen several metres vertically up over the India plate, creating shock waves in the Indian Ocean that travelled at up to 800 km/h (500 mi/h), forming tsunamis when they reached land.

• The epicentre of the earthquake was 155 miles from Banda Aceh, off the west coast of northern Sumatra, Indonesia

• Within hours had affected millions of people living along coastlines facing the Indian ocean

• The graphics below show how high the wave was as it arrived at different places around the Indian Ocean:

Satellite photographs of part of Banda Aceh, the nearest large settlement in Indonesia to the epicentre of the

earthquake and the one most affected by the Tsunami in terms of the amount of people who died

A street littered with vehicles and other debris near Patong

Beach in Phuket

http://youtube.com/watch?v=kGIz_-2UFJc&feature=related

Homework• Visit this website…

http://www.fema.gov/kids/tsunami/