EVALUATE AND COMMUNICATE 8. Discuss whether the earthquake event in Nepal supports the idea that the Himalayas are a young mountain range that is still forming. 9. Explain why living with earthquakes is something all New Zealanders have to do. Think carefully about how New Zealanders have to adapt to life with earthquakes. Describe how school in Christchurch might be different to school in Australia as a result. Answers and sample responses for this topic are available online.
LESSON 14.7 What is a tsunami?
LEARNING INTENTION By the end of this lesson, you should be able to: • investigate the causes and spatial distribution of tsunamis • define the key terms landslide and tsunami • explain why tsunamis are different to other types of waves.
Tune in FIGURE1 shows a beach in Thailand in 2004. The water had rapidly receded out to sea, puzzling onlookers. Moments later the devastating Indian Ocean tsunami hit the area, and many other locations, killing approximately 230 000 people. Discuss why the water might first disappear from the beach right before a tsunami.
FIGURE1 Hat Rai Lay Beach, Thailand, 26 December 2004
A tsunami is a large ocean wave caused by sudden motion on the ocean floor, such as an earthquake, a volcanic eruption or an underwater landslide. About 90 per cent of tsunamis occur in the Pacific Ocean, mostly due to earthquakes over 6.0 on the Richter scale. At sea, tsunamis are almost undetectable because they travel extremely fast (about 970 km/h) with a wavelength of about 30 kilometres and a wave height of only 1 metre. When tsunamis reach the continental slope, they slow down, wave height increases and wavelength decreases. The sea may recede quickly, indicating a tsunami is coming, and it’s best to head to higher ground immediately. A tsunami consists of multiple waves arriving at intervals of between 10 minutes and 2 hours.
386 Jacaranda Humanities Alive 8 Victorian Curriculum Third Edition
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