What Caused the Boxing Day Tsunami


The day of Dec. 26, 2004, started with an earthquake, off the coast of Sumatra, and only got worse as the resulting tsunami hit coastal nations throughout the Indian Ocean.

As TIME explained in a special issue devoted to the devastation, the geology behind the tsunami caused a chain reaction of disaster:

Geologists describe the tectonics–the almost imperceptibly slow movement of massive plates–of the southern Indian Ocean as complex because a number of plates converge there. The floor of the Indian Ocean–the Indian plate–is moving north at around 2.5 in. per year, about twice the rate that your fingernails grow. As it moves, it is forced under the Burma plate to its east. Eighteen miles below the surface of the ocean, stresses that had been gradually accumulating forced the Burma plate to snap upward. That was a huge geological event, eventually measured at 9.0 on the Richter scale. The dislocation…

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