Hwa Chong Institution
Integrated Humanities – Geography
Geomorphology
Handout 1: Tsunami
Aims & Objectives
- Define Tsunami
- Describe a Tsunami
- How Tsunamis are formed
- How to detect a Tsunami
- Effects of the 2004 Indian Ocean Tsunami
- What local authorities did to help the situation
What are tsunamis?
- Series of waves created when a body of water, such as an ocean, is rapidly displaced
- Derived from the Japanese terms tsu (harbour) and nami (waves)
What are the traits/characteristics of a tsunami?
- Wavelength of usually 200 km
- Speeds of over 800 km/h
- Due to the enormous wavelength, the wave oscillation at any given point takes 20 or 30
minutes to complete a cycle
- Has an amplitude of only about 1 m
- Difficult to detect over deep water
- Their passage usually goes unnoticed by ships
- A tsunami can occur at any state of the tide
- Even at low tide, a tsunami will still inundate coastal areas if the incoming waves surge high
enough
- Approaching the shore, a tsunami wave is compressed due to wave shoaling
- Forward travel slows below 80 km/h
- Wavelength diminishes to less than 20 km
- Amplitude grows enormously, producing a distinctly visible wave.
- What are the traits of a tsunami?
- The wave still has a wavelength of several km and the tsunami may take minutes to ramp up
to full height
- Open bays and coastlines adjacent to very deep water may shape the tsunami further into a
step-like wave with a steep breaking front
How are tsunamis formed?
- Formed by any of these processes:
o earthquakes
o mass movements above or below water
o volcanic eruptions
o underwater explosions
o landslides
o underwater earthquakes
o large asteroid impacts
o nuclear weapon tests at sea
- Can be generated when converging or destructive plate boundaries abruptly move and
vertically displace the overlying water
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Very unlikely that they can form at divergent (constructive) or conservative plate boundaries
Constructive or conservative boundaries do not generally disturb the vertical displacement of
the water column
Subduction zone related earthquakes generate the majority of all tsunamis
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First, there is a sudden shifting of continental plates creating earthquakes
This forces sea water above to rise, forming waves of 800 km/h
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As waves approach land, they slow to about 45 km/h
Squeezed upwards and causes increase in height
Tsunami waves then recede, dragging everything in its path
What are signs of a tsunami?
- There is often no advance warning of an approaching tsunami
- However, since earthquakes causes tsunamis, any earthquake occurring near a body of water
may generate a tsunami at appropriate conditions
- Bottom pressure sensors are anchored and attached to buoys to monitor the pressure of the
overlying water column
- Some areas might use tsunami warning systems to evacuate residents before the tsunami
strikes
- Some zoologists believe that animals have an ability to sense subsonic Rayleigh waves from
an earthquake or a tsunami
- Some animals seem to have the ability to detect natural phenomena
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Before the tsunami hit Sri Lanka in 2004 Boxing Day Tsunami, some elephants may have
heard the sounds of the tsunami as it approached the coast
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Naturally, they would run away from the noise towards inland
Case Study: 2004 Indian Ocean Earthquake
- Undersea earthquake that occurred at 00:58:53 UTC on December 26, 2004
- Epicentre off the west coast of Sumatra, Indonesia
- Magnitude to 9.3 (2nd strongest earthquake, 3rd deadliest earthquakes)
- Triggered a series of devastating tsunamis
- Tsunamis hit Indonesia, Sri Lanka, Thailand, Malaysia, Maldives, India, even as far as Africa
- Total of 230,210 dead or missing
Impacts
Economic Impacts:
- Coastal fishing communities and fisherfolk are devastated with loss of income, boats, and
fishing gear
- Estimated that 66% of the fishing fleet and industrial infrastructure in coastal regions have
been destroyed by the wave surges
- Affected shipping in Malacca Straits by changing depth of seabed
- Disturbing navigational buoys and old shipwrecks
- Countries affected by the tsunami have also suffered drop in tourists
- This is despite of most tourist infrastructure which is undamaged
- Tourists are reluctant because of psychological reasons
Environmental Impacts:
- Severe damage has been inflicted on ecosystems
- Spread of solid and liquid waste and industrial chemicals, water pollution and destruction of
sewage collectors and treatment plants threaten environment
- To assess the environmental impact would take a long time and significant amount of
resources
Responding to the disaster
Humanitarian Response:
- In India and Thailand, government and Civil Society Organizations were able to mobilize
resources and responded as quickly as possible
- India also provided assistance to neighbouring countries
- Was first nation to respond by sending naval ships and personnel to the neighbouring
countries due to the proximity
Indian Ocean Tsunami Warning System:
- Tsunami warning system set up to provide warning to inhabitants of nations bordering the
Indian Ocean of approaching tsunamis
- System became active in late June 2006 following leadership of UNESCO
- Consists of 25 seismographic stations relaying information to 26 national tsunami
information centres
- Consists of 3 deep-ocean sensors
Criticism:
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Many analysts claimed that the impact of the disaster would have been reduced if there had
been an effective warning system in place
People in some areas would have more than adequate time to seek safety
Many people had been inadequately housed
Large numbers of people were living in overcrowded temporary shelters of tents
References
- Wikipedia
- Google Images
- BBC
- CNN
- Chong, Marianne (2001). Aspects of Physical Geography. Singapore. Pekoe Books.
Adapted from the ACE presentation by:
Marcus Yiu 301
Ervin Lieu 302
Nicholas Chan 302
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