Small volcanoes erupt when molten rock rises from deep within Earth and then stalls in an underground chamber until enough pressure builds to blast it out to the surface. But the magma chambers of giant volcanoes—such as the one that erupted 2 million years ago beneath what is now Yellowstone National Park in the western U.S.—are too large for pressure from magma squirts to cause an eruption. Instead, the molten rock accumulates until its sheer buoyancy creates a different kind of stress, one that cracks open the top of the chamber and starts an eruption.
Posted on: Mon, 06 Jan 2014 22:00:01 +0000