The Yellowstone Plateau is a ‘geomorphic landform’ and there is no question that one day the restless giant will awaken and possibly erupt into a massive explosion. Magma which is molten rock from the Earth’s mantle has been at or near the surface for roughly 600,000 years. The resurgent domes inside the Yellowstone Caldera indicate that magma may be as little as 3–8 miles beneath Sour Creek Dome and 8–12 miles beneath at Mallard Lake Dome. The domes lift and subside when magma activity and hydro-thermal fluids well up or drop down and the frequency indicates just how volatile this Supervolcano can someday be.
When the first massive volcanic eruption occurred eons ago the volume of material ejected was approximately 6,000 times the size of the 1980 eruption of Mt. St. Helens. Approximately 1.3 million years ago, a second, smaller volcanic eruption occurred within the western edge and then 640,000 years ago, a third massive volcanic eruption created the Yellowstone Caldera, 30 by 45 miles in size.