FIGURE2 In 2004, an earthquake and subsequent tsunami in the Indian Ocean occurred along the boundary between tectonic plates.
The surge of water westwards pulled water away from coastlines to the east (e.g. Thailand), before it returned as massive waves.
Movement of plate
The slippage propelled a wave of water westwards towards Sri Lanka (reaching it about two hours later).
The pressure of tectonic plates pushing against each other forced one to slip under the other. The resultant 10 m-high bulge in the sea floor was almost 1300 km long.
Tsunamis can travel very fast — over 800 km/h. Land contours near the shore turn the rush of water into a massive wave (e.g. 10 m or more high).
Waves travelled as far west as Somalia and as far south as Rockingham, Western Australia.
The earthquake occurred about 7 km beneath the floor of the ocean.
SkillBuilder discussion Geographical inquiry 1. Explain why the scale of the Indian Ocean tsunami in 2004 was so large. 2. Use a world map to measure the distance the tsunami travelled from the source. 3. Research the impact this tsunami had on life and property across nations with an Indian Ocean coastline.
CASESTUDY The Japanese tsunami, 2011
The region of Japan is seismically active because four plates meet there: the Eurasian, Philippine, Pacific and North American plates. Many landforms in this region are influenced by the collision of oceanic plates. Chains of volcanic islands called island arcs are formed, and an ocean trench is located parallel to the island arc (see FIGURE3 in lesson 14.2). On 11 March 2011, an 8.9-magnitude earthquake struck near the coast of Japan. The earthquake was caused by movement between the Pacific Plate and the North American Plate. It occurred about 27 kilometres below the Earth’s surface along the Japan Trench, where the Pacific Plate moves westwards at about 8 centimetres each year. The sudden upward movement released an enormous amount of energy and caused huge displacement of the sea water, causing the tsunamis. When the tsunamis reached the Japanese coast, waves more than six metres high moved huge amounts of water inland. 19 747 people were killed and more than 120 000 buildings were destroyed. The direct financial damage from the disaster is estimated to be about $199 billion (about 16.9 trillion yen), according to the Japanese government.
TOPIC14 Geomorphological processes and hazards
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