Grímsvötn is a volcano in South-East Iceland. It is in the highlands of Iceland at the northwestern side of the Vatnajökull ice-cap. The caldera is at 64°25′N 17°20′W, at an elevation of 1,725 m (5,659 ft). Beneath the caldera is the magma chamber of the Grímsvötn volcano.
This picture show the magma chamber below Yellowstone. Computers show that there are no separate chambers and this chamber is much larger than previous beliefs. The magma chamber is the source of all the hydrothermal springs and geysers. According to researchers yellowstone erupted about 640,000 years ago making the caldera 30 by 40 miles wide. -- Caitlin Wolf