Boxing Day tsunami

Boxing Day 2004

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Why did the tsunami occur?

The tsunami occured because of the subduction of Ind-Aus plate underneath the Burma plate, raising it by 5 metres , lifting water out creating a tsunami. These plates collide at a rate of 6cm a year.

A tsunami is formed at a subduction zone where the leading edge of the overiding plate breaks free and springs seaward raising the seafloor and lifting water above it creating and starting a tsunami.

Was caused by an intial 9.1 magnitude (USGS) earthquake in the indian ocean because of the process of suduction (mentioned above)

The focus of this earthquake was 18km in the Beinoff zone - meaning it was shallow, another factor why tsunami did so much damage.

The last activity on this fault was in 1833, and scientists suggested the build up of pressure over recent decades caused the seafloor of the indian ocean to lurch 15 metres towards Indonesia , creating this megathrust earthquake where 1000km of the fault slipped.

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Characterics and nature of the tsunami

  • Wave length up to 150km
  • Rate of travel: 640-960km/h wave train
  • 30 cubic kilometres of water generated
  • 33ft waves in some places , 2 nd half inland in some places
  • Evidence of splay fault- enormous forces find weakenesses in the highly stressed crust and fractures through towards the surface. These faults may cause the seafloor to pump upwards producing a series of short waves. This was seen in Band Adeh where the wave hit 10 minutes after the earthquake.
  • Wave travelled a total of 3700 miles - 1/7th of the earths circumference.
  • 93 miles from Sumatra - meaning the earthquake took place at the supposedly inactive region of the Northern fault where no activity had taken place over 500 years.
  • Because of its enormous energy release and shallow rupture depth, the earthquake generated remarkable seismic ground motions around the globe, particularly due to huge Rayleigh waves that exceeded 1 cm (0.4 in) in vertical amplitude everywhere on Earth.
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Social Impacts:

  • 227,898 people were killed - 129 were british tourists - 130,000 alone in Indonesia
  • 1.7 million displaced
  • 316km road network destroyed
  • 1/3 of the tsunami victims were children


  • Total cost : U$ 14 billion , only $3.5 billion covered by insurance
  • Tourism in the region dropped:
  •  70% drop in tourist numbers in Jan 2005 compared to Jan 2004 in Maldives
  • 25 % drop in Sri Lanka and 15% drop in Thailand
  • First choice : tsunami cost them £1 million in returning tourists and ticket refunds


  • Raising of the sea floor reduced the capacity of the Indian ocean, producing a permenant rise in global sea level by 0.1 millimeters.
  • Waves travelled 3700 miles , 1/7 of earths circumference , displacing huge amounts of vegetation and animals.
  • 1000 mile rupture of fault
  • Some of the coral reefs which reduced the wave energy were damaged. The worst damage to carbonate coral reefs occurred in the northern and eastern islands, where in excess of 50% were badly affected
  • Forests are likely to die off as a result of saltwater intrusion
  • Some Landslides were noted.
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Human Factors producing the impacts

  • Wealth: lack of wealth in the region (GDP U$ 3004) in Indonesia suggests inability to protect or mitigate seen in the MEDC in Japan 2011. Therefore could not afford the sea walls, the tsunami warning buoys which they now have. Therefore thousands come have survived if they had warning.
  • Education: Lack of tsunami education also a big factor. If people knew what to do when an earthquake struck then many could have survived. Many were trying to pick up the rubble left from the earthquake or trying to find relatives trapped, they didnt realise a tsunami could come. Many were even on the beaches watching the waves coming in.
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  • Coastilisation: A big factor in why so many died and economic damage was caused. This is because tourism is the main income for economic growth in the affected countries. Therefore development on the coast with hotels, restauraunts , tourist resorts etc have meant fundamentally vulnerable to an open coast for a tsunami to strike. However, economy means that much to them, nothing else for income. Removal of mangroves could have limited the impacts here. According to the Newsletter of the wildlife conservation soceity of Tanzania (a country which was affected) it suggested that mangroves shield coastlines by reducing wave amplitude and energy. 30 trees per 100m squared area in a 100m wide belt may reduce maximum tsunami flow pressure by 90%. Food and Agriculture Organisation stated for the area of magroves in the 5 out of the 6 worst affected coutnries around the Indian ocean dropped by 26% between 1980-2000. Thailand , 65% mangrove was lost due to aquaculture mainly shrimp fishing and 26% due to coastal development.
  • Migration: many people in the poorer regions travel to the coast in search of work to pick up jobs in the tourism industry or on one of the ports fishing or trading, therefore incrasing the vulnerability of the population. Also India and Indonesia have the world's 2nd and 4th largest populations which contributed widely to the high death toll.
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