On Sunday morning, December 26, 2004 a powerful undersea earthquake struck off the north-western coast of Sumatra island, Indonesia. The 9.1 magnitude earthquake triggered a huge tsunami and became known as the Christmas or Boxing Day tsunami. The tsunami produced waves of up to 15 metres in height devastating coastal areas of several countries including Indonesia, Sri Lanka, India and Thailand.

Scientists say the earthquake was the third-biggest ever recorded, lasting up to 10 minutes and causing the Earth to vibrate up to one centimetre. It was so powerful that tremors were felt in India more than 2,000 km away while the tsunami caused damage in 14 countries including Somalia in East Africa more than 4,500 km west of the epicentre of the earthquake.

The earthquake occurred on a destructive plate boundary west of Sumatra. Here the Indian and the Eurasian plate meet and push towards each other at a rate of about 6 cm per year. In this case the Indian plate is dragged beneath the Eurasian plate. Stress and pressure builds up causing the edges of the plates to flex and deform. Eventually the pressure is released causing the earthquake. Refer to map below.

The movement of plates was sudden and massive and since it happened on the ocean floor it displaced an entire column of water vertically causing a tsunami. It displaced an estimated 30 cubic kilometres of water, unleashing a massive tsunami across the Indian Ocean. Quickly the tsunami waves were split into two one travelling out to sea and the other towards the coast. The diagram below explains how a tsunami is formed and why it is so devastating.

As we can observe in the diagram the quake occurred at a subduction zone where the Indian plate is forced down the Eurasian plate. As a result of the quake, the seabed was shifted up by several metres displacing water and causing the tsunami. Large waves travelled across the ocean in all directions at speeds of 800 km/h. As the waves approached land they slowed down to about 50 km/h, and increased in height. The tsunami waves crashed onto the coast and surged far inland causing great destruction.

The video below explains clearly what happens when the sea floor is pushed upwards, displacing a huge volume of water and creating devastating tsunami waves.

Within 15 minutes of the earthquake, waves began striking the coasts of northern Sumatra and the Nicobar Islands. Waves of up to 30 metres were recorded as the tsunami swept through Aceh, the hardest hit region of Indonesia. Around two hours after the earthquake struck, waves reached Sri Lanka, India and Thailand. An hour later they reached the Maldives, and- more than seven hours after the initial quake, the tsunami was observed in Mauritius and along the east coast of Africa.

The map below shows the effects of the Indian Ocean tsunami of 2004, the most deadly and destructive in recorded history.

No one knows exactly how many people lost their lives, but it is estimated that 220,000 people died as a result of the earthquake and the tsunami. Many of these were children who were swept away by the surging waves. Many tourists who were on the beaches of Phuket and Phi Phi Island in Thailand also lost their lives. More than 650,000 people were seriously injured and more than 2 million people were made homeless as whole coastal settlements were flattened. Thousands of people lost their jobs as tourist hotels in Thailand were destroyed and fishing vessels were washed ashore. The fishing and farming industries were also completely destroyed in some areas. Due to the scale of the disaster Injured people were left untreated for days and there was also an outbreak of diseases, such as cholera, due to a lack of fresh water supplies. As a result of the tsunami smaller islands in the Indian Ocean, coastal areas and whole fishing villages were devastated. Lines of communications, electricity and phone lines were cut off completely. In some areas roads and railways were destroyed. Estimates put the cost of the disaster at over £6 billion.

Watch this video which shows original footage caught on camera of the 2004 tsunami. It shows clearly how people were unprepared and how powerful the tsunami might be. We can clearly realise that nothing could withstand the destructive force of the incoming waves as they hit the shoreline.

Make a list of all the devastating effects of the tsunami as seen in the video.

The video below explains clearly why the Indian Ocean Earthquake and tsunami of 2004 was so deadly and devastating. It also refers to the long-term responses to predict such disasters.

The first giant waves from the Indian Ocean tsunami reached Banda Aceh, a city of about 300,000 people within 15 or 20 minutes after the earthquake. Few residents of the densely populated area realized that the earthquake they had felt could cause a tsunami, and there was little time to flee to higher ground. In the area at that time there was no tsunami warning system, a system which might have allowed them to evacuate areas in time. The only warning they received was the retreat of sea water from beaches before the wave hit. The countries hit by the tsunami of 2004 are rather poor and do not have the money to predict and plan in case of such an emergency. If people were informed that the wave was approaching many thousands of lives would have been saved.

Help poured in to the stricken countries from all over the world. It included fresh water, water purification tablets, food, blankets, tents, medical teams and supplies, machinery and expert assistance. Money donated by people around the world was used to rebuild houses, hotels, fishing boats and the infrastructure of the stricken countries. The Indian Ocean Tsunami Warning System was set up and became fully operational in June 2006.

Now work out the worksheet entitled Indian Ocean Earthquake and Tsunami Worksheet available in the resources section of this lesson.