The force of the magnitude 9 earthquake that struck northern Sumatra on December 26, 2004, may have caught much of the world by surprise. But scientists say the region has a violent geologic past and is ripe for more cataclysmic earthquakes and volcanic eruptions in the millennia to come.
The Indonesian island sits in an area of the Indian Ocean where several large chunks of Earth’s crust, known as tectonic plates, collide. Tectonic plates can slip past, beneath, and over the top of each other. In the Sumatra region, the Indian and Australian plates are slowly creeping alongside and–in a process called subduction–diving beneath, the Burma plate, part of the larger Eurasian plate.