What caused the tsunami? The next 5 lessons are about the Indian Ocean tsunami. This lesson we’ll see how it was produced by a massive earthquake off the coast of Sumatra. The earthquake was caused by two plates colliding with each other.

What happened? On 26th December 2004, a massive undersea earthquake was recorded in the Indian Ocean off the north-western coast of Sumatra in Indonesia. The earthquake produce a tsunami, a series of huge waves that devastated the coastal areas of Indonesia, Sri Lanka, Thailand, southern India, and islands in the Indian Ocean, with waves up to 15 metres in height. The earthquake was the fourth largest recorded in 100 years and was felt some 2,100 km (1,300 miles) away in India. The tsunami caused damage as far away as Somalia in East Africa, 4,500 km (2,800 miles) west of the earthquake’s centre. The most famous tsunami before that of 2004 followed the volcanic eruption of Krakatoa off the southern tip of Sumatra in 1883. The eruption caused the deaths of 36,000 people whilst the tsunami waves travelled several times around the world.

What caused the earthquake and tsunami? The outer crust of the earth is like a jigsaw. It is broken into huge pieces called plates. These plates move around very slowly. Where the plates meet they grind together and cause earthquakes. Volcanic eruptions also happen here. The Indian Ocean earthquake occurred just west of Sumatra where the Indian and Eurasian plates meet. As the plates moved towards each other they locked together and pressure built up. When the pressure was released there was an enormous earthquake. The plate movement on 26th December 2004 was both sudden and massive. The sea above the earthquake was pushed upwards causing a tsunami. The tsunami waves then spread rapidly out from the earthquake in all directions.

1. Sort the statements below into the correct order to show the causes of the tsunami disaster. Sea movement causes tsunami. Plate movement causes earthquake. Waves crash onto shore. Sea above earthquake forced upwards. Plates move towards each other. Tsunami waves spread quickly outwards.

2. Make a larger copy of the diagram below 2. Make a larger copy of the diagram below. a) Label the two plates, Sumatra and the Indian Ocean. b) Draw arrows to show plate movements. c) Label the earthquake position. d) Draw arrows to show the sea being pushed up and the movement of tsunami waves. e) Add a suitable title.

3. Using the box, in your own words, describe the main features of a tsunami.