An earthquake under the sea sent waves right across the Indian Ocean in a few hours.
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On the morning of 26 December 2004, a huge earthquake shook the sea floor near Sumatra, in Indonesia. It was magnitude 9.1. The sea floor jumped up and lifted the water above it.
Drag the hours slider and watch the wave spread across the Indian Ocean. Tap a dot to see when the wave got there. The wave front is drawn as a simple circle.
Out in the deep ocean a tsunami is low, and races along about as fast as a jet plane. Near the shore the water gets shallow. The wave slows down and piles up tall.
Sadly, many people died, in 14 countries. In 2004 there was no warning system for the Indian Ocean. Now there is one, fully working since 2011. It watches for big earthquakes and changes in the sea, and sends warnings fast.
The earthquake happened where one plate dives under another, on a branch of the Ring of Fire. Try the Ring of Fire lesson to see how!
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The globe pictures are simplified to show the idea. Earth images: NASA Blue Marble (public domain).
