Copper Band 12
What•is•a•tsunami?• TSUNAMIS
How•do•they•happen?• What•effect•do•they•have• on•people’s•lives?• Learn•about•how•we• can•predict•them•by• looking•at•the•science• behind•them•and•some• real-life•case•studies.••
Browse the complete Collins catalogue at
www.collins.co.uk
An•information•book
ISBN 978-0-00-820873-8
9 780008 208738 www.collins.co.uk/collinsbigcat
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Collins•Big•Cat•Inform•is• a•large•range•of•topical• non-fi•ction•to•support• the•curriculum.
Emily Dodd 6/19/19 8:23 PM
Written by Emily Dodd
Contents What is a tsunami?
2
Normal waves
4
Tsunami waves
6
Earthquakes and tsunamis
10
Case study: Boxing Day Tsunami, 2004
12
Landslides and tsunamis
14
Case study: Lituya Bay, Alaska, 1958
16
Volcanoes and tsunamis
18
Case study: Krakatoa, 1883
20
Predicting tsunamis
22
Living with tsunamis
24
Living after tsunamis
26
Glossary
28
Index
29
Tsunamis – causes and protection
30
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What is a tsunami? A tsunami is a fast, powerful, dangerous series of waves or wave. Tsunamis are usually caused by a movement of the seabed which pushes the water above it into waves. The waves start small when they are out at sea; you wouldn’t know it was a tsunami if you were in a boat floating on the water. But as the waves come towards the land, they increase in height and are powerful enough to bring large volumes of seawater inland causing flooding and devastation. The word “tsunami” means “harbour waves” in Japanese. Tsunamis are more common in Japan so that’s why we use their word for them. 2
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Normal waves Normal waves are caused by the wind pushing the water. The stronger the wind blows, the bigger the waves. wind
wind wind
tiny ripples
ripple
Waves are also created as tides slowly pull the ocean inland and away again every day. high tide
choppy sea
waves break
Fact Tides are caused by the pull of the moon and sun on the earth. low tide
4
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Tsunami waves Tsunami waves are different to normal waves in several ways. Tsunamis are much faster out at sea; they can travel over 800 kilometres per hour. They also have a longer period – there can be two hours between each wave. Typical tsunami wave versus normal wave normal wave
tsunami wave
wave speed
eight to 100 kilometres per hour
800 to 965 kilometres per hour
wave period
three to 20 seconds apart
ten minutes to two hours apart
wavelength
30 to 200 metres apart
100 to 500 kilometres apart
wave height
one to seven metres
three to ten metres
6
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