Restless Earth - Tsunamis

Restless Earth - Tsunamis

1. What is it?

   • A series of huge waves caused by the undersea displacement of a huge volume of water caused by an earthquake, volcano, rock slide, or other catastrophic event
   • Most tsunamis are caused by underwater earthquakes, but not all underwater earthquakes cause tsunamis
     • An earthquake has to be over magnitude 7.5 for it to cause a tsunami
   • About 90% occur in the Pacific Ocean
   • Can travel at 500 mph
   • Textbook Definition
     • A special type of wave wehre the entire depth of the sea or ocean is set in motion by an event, often an earthquake, which displaces the water above it and creates a huge wave
   • The main impact a tsunami has is flooding. The waters are also able to erode the foundations of coastal structures.

2. How is it caused?

   • When an earthquake, volcano or landslide happens on the ocean floor, water is displaced
     • This water forms the start of the tsunami
   • When the waves reach shallower water...
     • Their height can increase by several metres
     • The shallow water slows the wave
     • The waves get closer together

3. Case Study - Sendai, Japan 2011

   • Tsunami was secondary effect of earthquake
   • Magnitude 8.9
   • Quake lasted 5-6 minutes
   • Focus 6 km below water
   • Sendai City 130 km away from focus
   • Destructive plate margin
   • 2 Nuclear plants on the Pacific coast in Fukushima automatically shut down
   • Radiation releases caused large evacuations
   • 2,000 people confirmed dead
   • 4,700 homes destroyed
   • 91 countries offered aid