But Hawaiians don't need to worry about plunging into the magma below, say, during an earthquake—two miles of solid rock is more than enough to keep that from happening, according to geology undergraduate Julie Ditkof, who presented the findings December 14 at a meeting of the American Geophysical Union in San Francisco.

Ditkof, of Ohio State University, determined the chemical composition of crystals in a thousand samples of volcanic rock taken from Hawaii's most volcanically active regions, the Big Island (map) and an adjacent undersea volcano called Loihi. (Pictures: America's Ten Most Dangerous Volcanoes.)

Using a method developed in Iceland—another volcanic island—by Michael Barton, Ditkof's advisor and research partner at Ohio State, she paid particular attention