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Tsunami: Anatomy of a disaster

By Helen Lambourne

Last Updated: Sunday, 27 March, 2005

           

The wall of water

At 0059 GMT on 26 December 2004, a magnitude 9.3 earthquake ripped apart the seafloor off the coast of northwest Sumatra.

Over 100 years of accumulated stress was released in the second biggest earthquake in recorded history.

It unleashed a devastating tsunami that travelled thousands of kilometres across the Indian Ocean, taking the lives of more than 200,000 people in countries as far apart as Indonesia, the Maldives, Sri Lanka and Somalia.

A new BBC One programme, featuring the harrowing stories of survivors, gives a scientific account of the disaster.

THE EARTHQUAKE

Two hundred and forty kilometres (150 miles) off the coast of Sumatra, deep under the ocean floor, at the boundary between two of the world's tectonic plates, lies a 1,200km (745 miles) trench called the Andaman-Sumatran subduction zone.

At about the same speed as your fingernails grow, the lower plate, carrying India, is being forced or subducted beneath the upper plate, carrying most of South-East Asia, dragging it down, causing huge stresses to build up.

These stresses were released on 26 December. Shaking from this giant mega-thrust earthquake woke people from sleep as far away as Thailand and the Maldives.

Uplifted coral at Simeuleu (<I>Image: Prof Kerry Sieh, Caltech</I>)

Corals were lifted clear of the water, here at Simeuleu in Indonesia (Image: Prof Kerry Sieh, Caltech)

Unlike the more frequent strike-slip earthquakes of Kobe or Los Angeles, which last for a matter of seconds, subduction zone quakes last for several minutes.

The shaking during the Indonesian event went on for eight minutes.

Nobody knows how many died in the actual quake itself, but scientists have since visited the nearby island of Simueleu and found something astonishing.

The whole island has been tilted by the force of the earthquake, causing coral, submerged beneath the ocean for thousands of years, to be thrust out of the water on the east side; bays in the west have been drained.

"We were astonished to find ourselves walking through a pristine marine ecosystem, missing only its multitude of colours, its fish, and its water," said Professor Kerry Sieh, from the California Institute of Technology, US.

Yet, when the shaking from the earthquake subsided, no-one had any idea that the tremors had set in motion something far more deadly - a tsunami.

THE TSUNAMI

Deep under the Indian Ocean, at the epicentre of the quake, the 20m (65ft) upward thrust of the seafloor set in motion a series of geological events that were to devastate the lives of millions.

Billions of tonnes of seawater, forced upward by the movement of the seabed now flowed away from the fault in a series of giant waves.

          

Everything can be traced to the collision of two tectonic plates (Image: Royal Navy UK)

The only people in the world to have any idea what had happened were thousands of kilometres away on the island of Hawaii.

But, relying on seismic data alone, the scientists at the Pacific Tsunami Warning Center had no idea the earthquake had unleashed an ocean-wide tsunami.

It was a full 50 minutes after they first picked up the tremors that they issued a warning of a possible local tsunami.

Thirty minutes after the shaking had subsided, the first wave, travelling eastwards, crashed into Sumatra.

On the shores directly facing the epicentre, the waves reached heights of 20m (65ft), stripping vegetation from mountain sides 800m (0.5 mile) inland, capsizing freighters and throwing boats into the trees.

The city of Banda Aceh, just a few kilometres further round the coast was almost completely destroyed, killing tens of thousands of people in just 15 minutes.

WHAT THE ELEPHANTS KNEW

Leaving a devastated Sumatra behind, the series of waves continued across the Andaman Sea towards Thailand.

A herd of elephants in the mountains seemed to know it was coming. They began behaving strangely, stamping the ground and tugging at their chains, eventually breaking away to run to the hills.

Elephants have special bones in their feet that enable them to sense seismic vibrations long before we can. Animals taking to the hills was not the only sign that something was about to happen.

Due to the complex way in which the seafloor ruptured, some waves set off travelling with the crest first, others travelling trough first.

Barge on dry land (Prof Jose Borrero, USC)

The damage across the Indian Ocean region was immense (Image: Prof Jose Borrero, USC)

The trough, reaching the shores of Thailand, caused the sea to disappear off the beaches. It is one of the classic warning signs of an approaching tsunami.

Tragically, many tourists went down to the beach to look, some to rescue fish left flapping on the sand. A few minutes later, the first wave hit Thailand.

A thousand tonnes of water crashed down on each metre of beach. At Khao Lak, the wave reached 10m (30ft) and caused billions of pounds of damage. The human cost was far greater - nearly 5,000 confirmed dead and 3,000 still missing.

At the same time, the westbound series of waves were heading for Sri Lanka. In the deeper waters of the Indian Ocean, barely noticeable at just a 30cm (1ft) above the surface, they were travelling at some 800km/h (500 miles per hour).

SRI LANKA

The first wave hit Sri Lanka with no recede and no warning. The waves, up to six of them, weighing over 100 billion tonnes, rushed inland like a giant tide.

As they hit Sri Lanka's southern tip, they began to change direction, an effect called refraction.

The part of a wave closest to the shore slowed down in the shallow water, leaving the outer part, travelling at faster speeds, to bend around the island. The southwest coast of Sri Lanka, the side that should have been safe, was suddenly in the waves' direct line.

Cities such as Galle were destroyed; over 4,000 people died in this region alone.

The waves carried on further north to India, where they killed 10,000 people.

THE MALDIVES

Next in the waves' line, was one of the lowest lying countries on Earth - the Maldives.

Miraculously, although 80 people died here, this country escaped relatively unscathed.

It seems that due to their unique geography, being the tips of underwater volcanoes and without a continental shelf to push the wave height up, the tsunami just washed through.

Coral reefs are also thought to have protected the country, acting like a giant underwater colander, stripping the waves of energy.

As the waves left the Maldives, they passed through a narrow gap between the island chains, focusing their energy directly at Somalia, where 300 people lost their lives.

In Kenya, the waves, when they hit were small; their energy further removed by the land masses of the Seychelles and Diego Garcia.

They had also seen the news reports and evacuated the beaches; only one person died.

The last victim of a natural disaster that had claimed 300,000 with hundreds still unaccounted for.

Tsunami: Anatomy of a Disaster tells the story of 26 December 2004, why the waves were so devastating and what scientists are doing to prevent it happening again. The programme was broadcast on BBC One on Sunday at 1835 GMT.

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At-a-glance: Countries hit

Last Updated: Thursday, 22 December 2005

INDONESIA

Impact: Indonesia sustained the worst human losses and physical damage in the tsunami and earthquake of 26 December, 2004. The western tip of the island of Sumatra - the closest inhabited area to the earthquake's epicentre - was devastated. Some coastal villages are thought to have lost more than 70% of inhabitants. Much of the fishing and agricultural sectors in Aceh province was heavily damaged and 44% of people lost their livelihoods, according to the Asian Development Bank.

Toll: More than 130,000 people died, while at least 37,000 others remain missing. The exact number of victims will probably never be known. About 500,000 people were made homeless.

Aid: After the tsunami more than 160 aid organisations and UN agencies began operations in Indonesia to provide food, shelter and schooling. Foreign troops were also involved in initial emergency relief efforts. Agencies estimate a humanitarian response may be needed for up to two years.

One year on, Aceh's provincial capital, Banda Aceh, has been completely rebuilt, but there are still areas not far away which remain deserted wasteland. More than 60,000 survivors are still living in tents.

The UNDP says construction spending will soon reach approximately $2bn (£1.7bn) a year from current levels of $50m (£42m).

Correspondent's report: Aceh rebuilding gets on track

How survivors in Banda Aceh are re-building their lives

SRI LANKA

Impact: After Indonesia, Sri Lanka suffered more from the tsunami than anywhere else. Its southern and eastern coastlines were ravaged. More than 100,000 homes were damaged or destroyed, along with crops and fishing boats. The International Labour Organization estimates more than 400,000 people lost their jobs as a result - mostly in the fishing, hotel and tourism sectors.

Toll: More than 31,000 people died and more than 4,000 have been reported missing. More than half a million people were made homeless. In one of the worst incidents, more than 800 people died when a train was struck by the tsunami at Telwatta, in the south-west.

Aid: Nearly $3bn was pledged by international donors. But much of the aid has not been delivered because the government and Tamil Tiger rebels spent months wrangling over how to distribute it. When a deal was finally signed, it was promptly suspended by the Supreme Court which questioned some of its provisions. In the recent presidential election, voters frequently complained of delays in getting help. The problems are worse in Tamil Tiger-controlled areas.

Correspondent's report: Tsunami-hit orphanage rebuilt

Tension over aid in Tamil Tiger regions

INDIA'S SOUTH-EAST COAST

Impact: India's south-east coast was the worst affected part of the mainland when the tsunami struck and penetrated up to 3km inland. More than 150,000 homes were damaged or destroyed in Tamil Nadu, Andhra Pradesh and Kerala states, and in Pondicherry. (See below for more details on the Andaman and Nicobar islands.) More than 600km of roads and 14 bridges were damaged, according to the Asian Development Bank.

Toll: On the mainland, 8,850 people are confirmed dead - 7,983 of them in Tamil Nadu. (See below for data on the Andaman and Nicobar islands). It is estimated that almost 70,000 people are in relief camps or centres on the mainland.

Aid: Repairing the damage was expected to cost about $1.2bn. India has provided aid to other countries hit by the tsunami. Initially it refused outside help itself. Donations of fibreglass boats to some fishing communities have helped revive their livelihoods. Also, with the high demands for boats and catamarans, many fishermen have taken up boat-making as a part-time occupation. Aid agencies say the rehabilitation efforts in the state are generally positive. But thousands are still living in uncomfortable pre-fabricated tin shelters and do not have permanent homes. Government rules that new homes must be built at least 500 metres away from the sea have made fishing communities unhappy. Another major concern is the agricultural community which lost 5,000 hectares of farming land to the tsunami.

Correspondent's report: Turning back the tide of grief

Indian government refuses international aid

INDIA'S ANDAMAN AND NICOBAR ISLANDS

Impact: The remote islands, lying about 1,400 km from the mainland but only 100km or so from the epicentre, suffered extensive destruction. Salt water contaminated many sources of fresh water and destroyed large tracts of arable land. Many jetties - vital for getting supplies into the islands - were destroyed.

Toll: Almost 1,900 islanders were confirmed dead from a population of some 400,000. More than 5,550 are still missing - the bulk of them from Katchall island.

Aid: India refused international assistance to the strategically important Andamans where it has sensitivities over its military base. There have also been concerns that poorly planned reconstruction work would damage the lives of various tribal groups there. Local people and NGOs say money has not been spent well, and there have been accusations of contractors profiteering. More than 10,000 people are still living in pre-fabricated tin shelters ill-suited to the climate and their requests for tools and wood to build their own shelters has been ignored by the government. Some people were given 10,000 rupees ($232) to replace their fishing boats, but complain that the boats cost 10 times more than that.

Correspondent's report: Andaman victims still homeless

Islanders' anger at relief delays

THAILAND

Impact: The west coast of Thailand was severely hit, including outlying islands and tourist resorts near Phuket.

Toll: Some 5,395 people have been confirmed dead. They include about 2,400 foreigners from 36 countries. The number of people still missing exceeds 2,800. Some bodies may still lie in the rubble of wrecked hotels and their environs.

Aid: Thailand did not ask for disaster relief aid, but it has requested technical help to identify the dead - a vast task that is still continuing.

However, more than 3,500 volunteers from more than 50 countries have volunteered their services to help Thailand recover over the last year.

Rebuilding has been rapid along Thailand's west coast, which is heavily dependent on tourism.

The UN has praised the Thai government's response, but notes that rampant tourism development is once again in evidence, and that other issues such as land disputes still need to be resolved.

Its report, a year on from the tsunami, finds that the fishing industry suffered far heavier losses than the tourism industry - about $267.8m (£226.3m).

The Thai government has provided more than $1bn in aid, while international aid has totalled $69m (£58.3m).

Correspondent's report: Thailand rebuilds after tsunami

Many people have been left with no livelihood

MALDIVES

Impact: The extremely low-lying Maldives consist of 199 inhabited islands, 20 of which were described as "totally destroyed" by the tsunami. Well over 4,000 homes were destroyed or damaged. Schools, boats, infrastructure and tourist resorts also suffered.

Toll: At least 81 people died. The impact on the country's economy was huge.

Aid: The Maldives government puts rebuilding costs for homes and infrastructure at about $375m - but so far sums pledged fall well short of this.

Paradise lost? Tsunami's impact on the tourist industry

MALAYSIA

Impact: Shielded by Sumatra, Malaysia's coastline was spared widespread devastation despite being close to the epicentre. Fewer than 10,000 people are believed to have been affected, although scores were swept from beaches near the northern island of Penang.

Toll: At least 68 people confirmed dead.

Correspondent's report: Mystery of tsunami aid

BURMA

Impact: The worst affected area was the Irrawaddy Delta, inhabited by poor subsistence farmers and fishing families.

Toll: Burma's military junta puts the death toll at 61, but the World Food Programme (WFP) says this may be an underestimate. One WFP employee found 200 households where at least one person was missing. Hundreds of Burmese migrants workers living in Thailand are also thought to have died.

Correspondent's report: Thailand's secret survivors

BANGLADESH

Toll: Two people were reported dead in Bangladesh.

SOMALIA

Impact: Somalia was the worst-hit African state. Damage was concentrated in the Puntland region, on the tip of the Horn of Africa. Water destroyed 1,180 homes, smashed 2,400 boats and rendered freshwater wells and reservoirs unusable, the UN said in a report early in January.

Toll: Between 150 and 200 Somalis are thought to have died, with thousands more homeless and many fishermen unaccounted for. As many as 30,000 people may have been displaced.

Aid: The UN has called for $13m to help tsunami victims. Aid agencies with small ground operations in Puntland delivered food and relief supplies, as did a German Navy helicopter.

Correspondent's report: Somalis struggle to rebuild lives

Somalia's tsunami victims make plea for aid

KENYA

Toll: One person drowned in Kenya.

TANZANIA

Toll: Ten people were killed in Tanzania.

SEYCHELLES

Toll: One person was killed in the Seychelles.