Tsunami

A tsunami is a giant sea wave caused by the large-scale displacement of water.
Tsunamis are triggered by four events:
Earthquake, landslide, volcanic eruptions (Krakatau 1883) and meteorites.

In all four cases the tsunami is triggered by the displacement of water. As the seafloor lifts, it displaces billions of tonnes of water above it.
Seconds later, the tsunami undergoes rapid transformation as the displaced water column collapses and splits.
The water rushes away from the uplifted area creating a tsunami wave that is travelling radially outwards from the centre.
The wavelength of a tsunami in open water can be up to 200-300km. Since the wave travels up to 100km/hour with a wave height of less than 1m, fishermen in a boat would hardly notice the wave passing beneath them.
As the tsunami nears land the front of the wave slows to around 200km/hr and is caught up by the back of the wave still travelling over 800km/hr.
As a result, the front of the wave starts to increase in height in a process known as amplification.
The edge of the water can recede up to 1mile out to sea as water is sucked into the wave by draw down. This is the first sign of an approaching tsunami. When the tsunami reaches land, its effects depend upon:
Height of the wave.
Distance the wave has travelled.
Length of the event that triggered the tsunami.
Extent to which warnings are given.
Coast, physical geography such as gradient of sea bed.
Direction of wave approach.
Population density in affected areas.

2004 Boxing Day Tsunami

Where and when?
Sunday, 26 December 2004, with an epicentre off the west coast of Sumatra, Indonesia.
Plates involved?
Indo-Australian and Eurasian.
Type of margin?
Subduction – Indo-Australian being subducted.
How many killed?
220,000.
Cost of damage.
US $ 9.9 billion.
0 on the Richter scale.

Effects

Months later rubble and debris still remained.
Wave hitting the beach was the highest ever recorded – 60ft above the waterline.
Earth orbit was altered, and the day was made 2.68 microseconds shorter.
Nicobar Islands shifted laterally 1.25m and sunk by 1m.
12 countries directly affected in total.
Somalia was hit by a worse wave despite being further away.
Many coastal populations were taken by surprise due to complete lack of tsunami warning system in the Indian Ocean- as it is surrounded by mainly LEDC’s who cannot afford the system for such a low frequency event
Death toll of approximately 228,000 with 170,000 of these being Indonesian.
Widespread destruction of infrastructure was caused, including the destruction of power transmission and clean water and sewerage pipes. 82% of roads were either flooded or destroyed, making them impassable.
High population density and tropical climate meant diseases were transmitted fast – Cholera, Dysentery, and Hepatitis.
Many lefts without shelter sanitation, drinking water and food.
Many communities affected were dependent on the fishing industry, which employs 250,000. And so, there was a loss of income earners, fishing equipment, and ships damaged.
Farming industry could not operate productively as irrigation is difficult and many fields were swamped with salt water.
Coastal ecosystems such as coral reefs, and forests were destroyed.
Arable land was covered in a layer of slat, which made in infertile.
Many hundreds of thousands injured or suffering from trauma and the grief of losing family members.
Waves travelling to Sir Lanka were travelling at around 500mph towards its east coast.
100 billion tonne waves struck the Sir Lankan coasts every half hour.

Short Term Responses

The pacific tsunami warning centre picked up data first about the earthquake. They issue a bulletin stating that the earth occurred outside the pacific and no tsunami threat existed to them.
Just 15 minutes after the bulletin was released the Hawaii coast was hit and they realized the quake was six times greater than first thought.
Co-ordination and transportation by plane of critically important relief supplies such as food, water, water containers, medical supplies, tents, fuel and batteries.
Civilian teams of 24 doctors, specialists and laboratory technicians.
A water purification plant set up to produce up to 480,000 litres of water a day in Banda Aceh.
A total of $14 billion was received.
US provided aircraft for search and rescue, surveying and transport of aid cargo such as food, shelters and dry ice to preserve the dead.
The government of the affected countries reacted reasonably quickly but in many cases were reliant on outside aid due to the magnitude of the disaster and the lower level of economic development of the places affected.
The USGS managed to get a warning to Africa which saved lives.
Action aid raised £13 million and immediately sent food aid of many governments.

Long Term Responses

Many people have re-established buildings and businesses in the affected areas
An early warning system has now been put in place in the Indian Ocean, through co-operation of governments
Many conservation groups have been helping to protect mangroves and replant vegetation in coastal areas.
The Thai government also improved signage for evacuation routes and carried out more drills to prepare for future tsunami.
The UN has agreed back plans for the Indian Ocean tsunami plan.
Many lives could have been saved if there was education about tsunamis, and what to do if one struck the island, there was no gauges in the Indian ocean which detect tsunami waves, and there were no specific contact points in which warning systems could have told people to evacuate the coastal areas and reach higher ground.