Did you know that Yellowstone National Park is actually an active supervolcano? As you walk around the park you may think: “I don’t see any volcanos?!” That’s because much of the entire park is a volcano – and the bubbling geysers and hot springs are an indication of the churning activity below the surface.
The term “supervolcano” implies an eruption of magnitude 8 on the Volcano Explosivity Index, indicating an eruption of more than 1,000 cubic kilometers (250 cubic miles) of magma. Yellowstone has had at least three such eruptions: The three eruptions, 2.1 million years ago, 1.2 million years ago and 640,000 years ago, were about 6,000, 700 and 2,500 times larger than the May 18, 1980 eruption of Mt. St. Helens in Washington State.
The last time the Yellowstone supervolcano erupted was 640,000+ years ago. The Yellowstone eruption area collapsed upon itself, creating a sunken giant crater or caldera 1,500 square miles in area. The magmatic heat powering that eruption (and two others, dating back 2.1 million years) still powers the park’s famous geysers, hot springs, fumaroles, and mud pots.