At his website, “A Writer’s Almanac,” Garrison Keillor writes:

On this date in 2004, a tsunami devastated coastlines along the Indian Ocean. It was triggered by an earthquake in the middle of the ocean, 160 miles west of Sumatra. With a magnitude of between 9.1 and 9.3, the quake was the third strongest ever recorded on a seismograph, and it lasted for up to 10 minutes. It occurred when pressure built up along a 600-mile fault line between two tectonic plates to such a degree that one plate slipped underneath the other. The quake occurred in relatively shallow water, which meant that the energy was not dispersed as much as it would have been in deeper seas. The U.S. Geological Survey estimates that the quake released energy equivalent to 23,000 Hiroshima-type atomic bombs. The quake was so powerful that it vibrated the whole planet and actually changed the Earth’s rotation very slightly.

The shifting of the plates raised the sea floor by about 10 yards, and this displaced massive amounts of water. The tsunami chain that this generated reached the Sumatra coast within 15 minutes. The waves — which started small but grew as high as 50 feet — wiped out whole villages in seconds. The tsunami even claimed lives in South Africa, up to 3,000 miles away from the epicenter of the quake. An estimated 230,000 people from 14 different countries died; half a million more were injured. Five million people required humanitarian aid. A ship weighing almost 3,000 tons was thrown almost a mile inland, where it remains a tourist attraction in Indonesia. But there were very few animal casualties; many people reported seeing animals fleeing for higher ground just minutes before the tsunami struck.

Two years after the quake and tsunami, the Indian Ocean Tsunami Warning System went into operation, and it was successfully put to the test in 2012, when more quakes hit the Indian Ocean.