Throughout history, humans have been fascinated with and impacted by volcanoes, which can range from minor rumblings to climate-changing spasms of the Earth.
The earliest known depiction of a volcano is on a wall painting in Anatolia, Turkey, and is estimated to be about 9,000 years old. The painting shows a cluster of houses below a twin-peaked volcano during an eruption.
The most deadly eruptions had few witnesses. Those were the supervolcanoes, with a Volcanic Explosivity Index (VEI) of 8 or above. The VEI is an index of how much volcanic material is ejected, to what height, and how long the eruption lasts. The open-ended scale runs from 0 to 8 and is logarithmic, similar to the Richter Scale used to measure earthquakes.
There have been numerous supervolcanic eruptions, the most recent being 75,000 years ago at the Toba Caldera in Sumatra, Indonesia, which is now the site of the world's largest volcanic lake. The eruption changed the climate of the Earth by plunging it into a winter lasting three to four years. Its Dense-rock equivalent (DRE, total volume of material erupted) was 2800 cubic kilometers. In comparison, Mount St. Helens had a DRE of 0.25 cubic kilometers.
Although the last supervolcanic eruption occurred thousands of years ago, that doesn't stop volcanologists from studying active supervolcanoes. The most volcanic place known to man is not on Earth, but in space, where Jupiter's moon Io has several hundred active volcanoes, several of them supervolcanoes. The largest, known as Loki, is the size of Connecticut, and its volcanic plume extends up to 250 miles above the surface, in comparison to volcanic plumes on Earth, which reach up to 25 miles.
Of the 47 known eruptions on Earth thought to have a VEI of 8 or above, Yellowstone is among them. Yellowstone is classified as a supervolcano, capable of producing an eruption that ejects mass more than 1,000 cubic kilometers (240 cubic miles). This is thousands of times larger than most of the volcanic eruptions throughout history.
There are actually three known supervolcanoes in the United States: Long Valley Caldera in eastern California and Valles Caldera in northern New Mexico are the other two. Both are still active.
New research from Washington State University and the Scottish Universities Environmental Research Centre indicates that the cataclysmic Yellowstone eruption that created the Huckleberry Ridge deposit was not one giant eruption, but two smaller eruptions thousands of years apart. The first and larger eruption, which occurred about 640,000 years ago, produced a volume of 2,200 cubic kilometers of ash, almost 10,000 times greater than Mount St. Helens, maintaining Yellowstone's status as a supervolcano.
What this means, however, is that the volcano is more active than previously thought. Because past performance is a predictor of future performance in the life cycle of a volcano, volcanologists may have to rethink the projections of what Yellowstone may do in the future.