Look at the picture above. What is the message of this international warning sign??
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Definition of a Tsunami
A tsunami is a series of seismic sea waves that have enormous energy, momentum and destructive power.
The word comes from two Japanese words meaning ‘Harbour Wave’.
Source: http://www.bom.gov.au/tsunami/info/index.shtml, Thinking Geography (Berry, 2007)
The Birth of a Tsunami
Underwater earthquakes are the most common cause of a tsunami. Tsunami can also be caused by
volcanic eruptions, coastal or submarine landslides or asteroid/meteorite impact.
To understand tsunami, we have to understand the theory of plate tectonics, which suggests that a series
of huge plates makes up the lithosphere, or top layer of the Earth consisting of the crust and upper mantle.
These plates make up the continents and seafloor. They rest on an underlying viscous layer of molten rock
called the asthenosphere.
On the Earth, these plates are constantly in motion, moving along each other at a speed of 2.5 to 5 cm per
year. The movement occurs most dramatically along the edges of the plates called fault lines. The
movement of the tectonic plates causes earthquakes and volcanoes.
When two plates come into contact at a region known as a plate boundary, a heavier plate can slip under a
lighter one. This is called subduction. Underwater subduction often forms deep ocean trenches along the
seafloor. In some cases of subduction, part of the seafloor connected to the lighter plate may "snap up"
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suddenly due to pressure from the sinking plate. This results in an earthquake. The focus of the earthquake
is the point within the Earth where the rupture first occurs, rocks break and the first seismic waves
generate. The epicenter is the point on the seafloor (or other part of the Earth's surface) directly above the
focus.
When this piece of the plate snaps up and sends tons of rock shooting upward with tremendous force, the
energy of that force transfers to the water. The energy pushes the water upward above normal sea level.
This is the birth of a tsunami. The earthquake that generated the December 26, 2004, tsunami in the Indian
Ocean had a magnitude of 9.15 – the deadliest in recorded history.
Source: http://science.howstuffworks.com/nature/natural-disasters/tsunami2.htm
Your Task.
1. What is a tsunami? __________________________________________________________________
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2. What are the most common causes of tsunamis? _________________________________________
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3. Briefly explain how an earthquake causes a tsunami. Use the following terms - tectonic plates,
subduction. ________________________________________________________________________
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Travelling Waves
Tsunamis travel outwards from the original zone of the earthquake and move at speeds of more than 800
km an hour. They can reach land thousands of kilometres away from the epicentre of the earthquake. As
tsunamis approach land and the water depth becomes shallower, the tsunami slows down but the height
of the wave increases.
The map below shows the time in hours for the Indian Ocean Tsunami (2004) to travel from its point of
origin off the coast of Indonesia (marked with red dots) to other locations in the Indian Ocean. This
tsunami also affected the Australian continent even though it was thousands of kilometres away. Tsunamis
affect the Australian coastline about every two years – most of these are regarded as low risk in terms of
damage and loss of life.
Source: http://www.bom.gov.au/tsunami/info/travel_time.shtml
Your Task.
1. Calculate approximately how many hours the tsunami took to travel to: Sri Lanka __________; the
west coast of India ____________; Somalia (east Africa) ____________; west coast of Australia
___________; Melbourne, Australia _____________; the nearest tip of Antarctica __________.
2. What factors affect how fast a tsunami travels? _________________________________________
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Impacts of Tsunamis
Source: http://www.smh.com.au/environment/weather/like-a-bad-dream-sirens-prayers-and-sorrow-as-tsunami-disaster-remembered-20120312-1utt5.html
Japan, March 11, 2011. At least 440 people died and a quarter of the town's buildings were destroyed as
the tsunami waves, funnelled into the tight V-shaped bay of Onagawa. Water continued to rush almost two
miles inland, growing to a height of more than 20 metres. The three photos below show an aerial view of
Onagawa, Miyagi Prefecture, Japan, taken before (top), soon after (middle), and nearly one year after
(bottom) the devastating earthquake and tsunami of March 2011.
Your Task: Annotate the 3 photos below to indicate environmental and economic impacts of the tsunami.
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Major Killer Tsunami Origins in Recent History
Source: http://users.tpg.com.au/horsts/tsunami_hazard.html
Your Task: Compare the map above, showing the origins of killer tsunamis, with your map of tectonic plate
boundaries and earthquake zones. Describe the spatial association (connection) between tectonic plate
boundaries and tsunamis, using plate names and examples of Tsunamis from the two maps.
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Responding to a Tsunami
The obvious strategy in dealing with a tsunami is to avoid them. In order to do this, people living in coastal
areas need advance warning of when a tsunami is going to happen. Most tsunamis occur in the Pacific
(Ocean) region because of the tectonically active area called the Pacific Ring of Fire. The Pacific Ocean
Tsunami Warning System (POTWS) was established in 1965 to (1) measure earthquakes and changes in sea
level, (2) calculate the tsunami’s path and travel time, and (3) issue tsunami warnings to nations in the
Pacific Basin.
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A large scale tsunami disaster shocks and unites the world in an effort to help survivors. There are four
phases in the provision of disaster relief. Phases 1 and 2 are short term occurring immediately after the
disaster. Phases 3 and 4 occur in the medium and longer term.
Phase 1: Emergency life-saving. Local people, government, military and relief workers from many nations
search for missing people, care for the sick and injured and bury the dead. The immediate needs are safe
food and drinking water, medicine, clothes and shelter. Communication with the world is important.
Phase2: Relief efforts. Survivors need temporary shelters, a temporary source of electric power, food and
water brought in. The huge clean-up operation begins with machinery and people brought in to help.
Phase 3: Rehabilitation. Temporary houses and schools need to be built. Water, electricity and sewerage
needs to be re-established. Local businesses need help to start again.
Phase 4: Reconstruction. Permanent house, business and factories are rebuilt. Hospitals and schools are
restored. Roads, bridges, railways and airports are rebuilt. Residents are helped to find permanent
employment and rebuild their lives.
Your Task: Insert the following words/phrases into the appropriate boxes below to show what activities might
occur in each of the four phases of disaster relief following a tsunami. Some things may fit in more than one box.
Rebuild permanent houses
Rebuild airports
Clean-up operations Search for missing people
Volunteer aid workers assist Armed Forces keep order
Temporary shelters erected
Bury dead
Electricity generators set up Build roads and bridges
Help survivors find jobs
Set up first aid
Deliver food and clean water Rebuild factories and business Prevent disease
Establish communication
Establish permanent water, sewerage and electricity supplies
Water purification kits Plants crops
Establish shops and trade
Supply clothing
Clear building rubble Build new schools
Phase 1: Emergency life-saving (Short term)
Phase 2: Relief Efforts (Short term)
Phase 3: Rehabilitation (Medium to long term)
Phase 4: Reconstruction (Medium to long term)
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