Pacific Ocean; The Oceans; Scientific American Presents; by Staff Editor; 2 Page(s)

Named by Portuguese explorer Ferdinand Magellan, who believed it to be free of violent storms, the Pacific Ocean is not, in fact, so pacific. Its tropics can be roiled by typhoons, and its shores can feel the brunt of tsunamis-great waves generated by earthquakes. Traveling much faster than any of the Pacific's normal currents (right), tsunamis cross the open ocean at the speed of a modern jet. Yet they cannot be seen or felt far from land: only when tsunamis reach the shallows do they build into monstrously tall walls of water.

The Pacific is particularly prone to tsunamis because its underlying tectonic plates continually push under adjacent continents and seas at subduction zones. These collisions are marked by oceanic trenches such as the Mariana Trench (right), which includes the deepest spot on the earth. Grinding against one another along the periphery of the basin, the crashing plates cause powerful temblors.