Textbooks have long offered students an explanation of volcanoes that's totally wrong—or so say scientists who are offering a very different theory, Caltech reports. The standard explanation depends on the existence of long, narrow columns or jets of magma known as mantle plumes. Since about 1990, they've been largely accepted among geologists, Caltech professor Don Anderson tells the Huffington Post. The thinking was that molten rock near the Earth's core shot up to the planet's mantle in these plumes, believed to be less than 186 miles wide. Gizmodo explains what was thought to happen next: "Where those columns sit in the mantle, there are hot spots—and when the Earth’s stiff crust fractures slightly, the magma can burst up and out as a volcano."
Thing is, those mantle plumes just don't exist, the experts say; indeed, the plumes have "never had a sound physical or logical basis," says Anderson. "They are akin to Rudyard Kipling's Just So Stories about how giraffes got their long necks." So what's really happening? According to Anderson's team, the new data indicates that there aren't narrow columns at all, but slow-moving "upwellings" that can be thousands of miles across. And instead of heat from the planet's core causing the motion, cooling at the surface is responsible for the movement: The cooling causes chunks of mantle to sink, and the less-dense magma is displaced and pushed upward. Thanks to cracks and stresses in the Earth's plates, the magma can be squeezed out of the Earth like a sponge. (Click to read about another unusual volcanic discovery.)