The Yellowstone Caldera, sometimes known as the Yellowstone supervolcano, is a volcanically active region in Yellowstone National Park. It measures 55 kilometers (34 mi) by 72 kilometers (44 mi). Yellowstone, like the Hawaiian Islands, is believed to lie on top of one of the planet's few dozen hotspots where light hot molten mantle rock rises towards the surface. The Yellowstone hotspot has a long history. Over the past 17 million years or so, successive eruptions have flooded lava over wide stretches of Washington, Oregon, California, Nevada, and Idaho, forming a string of comparatively flat calderas linked like beads, as the North American plate moves across the stationary hotspot. Currently, volcanic activity is exhibited only via numerous geothermal vents scattered throughout the region, including the famous Old Faithful Geyser, but within the past two million years, it has undergone three extremely large explosive eruptions, up to 2,500 times the size of the 1980 Mount St. Helens eruption.