Haiti

About six weeks ago, a large earthquake devastated Haiti and killed over 200,000 people. Saturday, a huge earthquake releasing 500 times more energy, devastated Chile and killed hundreds.

So why did the smaller earthquake kill so many more people? And why the sudden spate of disastrous earthquakes in the Americas?

No, the apocalypse is not coming. No, the two earthquakes are not linked in any way. And no, Pat Robertson, you can't blame the Devil or the French. The real answers, for those comfortable with science and the Enlightenment, are tectonics and poverty.

Of the many revolutions of the 1960s, the one that really mattered to geologists was the revolution of plate tectonics. Tectonics is the word geologists use to describe the process by which mountains move and rocks squeeze and crunch.

In the sixties, new data from research cruises and from earthquake seismometers led to the realization that tectonics makes mountains slide sideways long distances. Earth scientists discovered that the Earth has a patchy skin of mobile plates a hundred miles thick and thousands of miles across, and that they move horizontally at a slow but irresistible pace. It's where they collide that our problems begin.

South America is a prime example of this process, one that geologists call "subduction." It's why we have the long chain of mountains called the Andes and it's why countries like Chile and Peru suffer giant, destructive earthquakes every few decades.