There's more to Yellowstone National Park than meets the eye. Much more, as it turns out.You might already know that a supervolcano dominates the famous park that is situated on land in Wyoming and Montana. A shallow subsurface magma chamber has long been known.But now a second, much larger reservoir of partially molten rock has been discovered by researchers at the University of Utah. There's enough magma inside, they say, to fill the Grand Canyon more than 11 times.