Four Supervolcanoes Beyond Yellowstone and What the Term Really Means

Kincaid begins by asking viewers to think of a supervolcano, and says the first example that comes to mind is likely Yellowstone. Yellowstone is indeed known for massive supervolcanic eruptions, but Kincaid stresses that it is not the only one.

According to Kincaid, there are so many large volcanic systems around the world that a single list could not cover all of them. These volcanoes have produced some of the biggest eruptions in the planet's history, eruptions that could cover an entire country in ash, form massive volcanic craters and even alter the course of entire species. The video then introduces four volcanoes that viewers may not have heard of.

Kincaid says the term 'supervolcano' is extremely controversial among volcanologists, many of whom dislike it, and she includes herself among them. The more precise jargon term is 'supereruption', and an eruption has to meet a specific threshold before it earns that name.

Kincaid says media outlets often label volcanoes as supervolcanoes even when they have never had a supereruption. Even among volcanoes that have had one, most have had only one in their entire history, which she says makes the term misleading. Yellowstone is one of the few that has had multiple supereruptions, but it has not produced them continuously, and most of its eruptions are not supereruptions. She adds that its next eruption will probably be fairly underwhelming.

The first volcano is Mount Aso in southwest Japan. Kincaid says it is fairly large for a volcano, but it sits inside an even larger volcanic crater, the 24-kilometer-wide Aso Caldera. A caldera forms when part of a volcano collapses in on itself, usually during or shortly after an eruption.

Kincaid notes that most major cities would fit inside that crater, and that multiple farms and pastures lie within its boundaries. The caldera also contains 17 volcanic cones, and 38 eruptions have occurred there since 1950. Only one of those cones is considered active, and its most recent eruption was in 2021, which Kincaid describes as not particularly dangerous. She also mentions that a news outlet called Aso a 'Supervolcanic "Hell" Caldera', a label she treats as misinformation and not a joke.

About 90,000 years ago, Aso had the last of four major eruptions that formed the caldera. Volcanologists call this one Aso-4, which Kincaid says undersells it, since it is the second largest volcanic eruption Earth has experienced in the last 100,000 years. It produced more than 600 cubic kilometers of volcanic material, enough to cover nearly the entire Japanese Archipelago in anywhere from 15 centimeters to several meters of ash and other material, depending on distance from the volcano.

Kincaid explains that ash volume is one indicator used to classify eruptions through the Volcanic Explosivity Index (VEI). The VEI is based on the volume of ash erupted, the height the ash plume reached in the atmosphere, and how long the eruption lasted, and it ranks eruptions on a scale of 0 to 8.

Kincaid compares the Vesuvius eruption that buried Pompeii and the 1980 eruption of Mount St. Helens, both of which she classifies as VEI 5. The three other caldera-forming eruptions at Aso were somewhere in the VEI 6 to 7 range.

Kincaid says that a volcano reaching an 8 qualifies for supereruption status. Aso reached that level roughly 90,000 years ago with Aso-4 and has never done so again.

Kincaid anticipates that viewers might assume every supereruption reaching VEI 8 must also be maximally deadly and apocalyptic. She says that assumption would be wrong. In her account, scientists have tried to link a supereruption to a global mass extinction, but the evidence does not point that way and no supereruption has been successfully linked to one.

She adds that this is not especially reassuring for animals living right next to the giant volcanoes.

Taupo sits in the middle of New Zealand's North Island and has had one VEI 8 supereruption more than 25,000 years ago, along with a VEI 7 eruption about 2,000 years ago. Kincaid says that in addition to a massive ash plume, island residents faced another hazard.

She describes a pyroclastic flow as a dense, hot mass of lava blocks, ash and volcanic gases rushing down a volcano's slopes at speeds up to 700 kilometers per hour and at temperatures over 800 degrees Celsius. Taupo's supereruption produced a pyroclastic flow that reached more than 100 kilometers downhill from the volcano's peak. Kincaid says many local animal and plant populations were wiped out or nearly so.

Kincaid points to the North Island brown kiwi, which is the unofficial national bird of New Zealand and the nickname for the people who live there. Four genetic lineages of this species cross the island. They are similar enough to be one species but different enough that researchers can tell them apart. One group of scientists hypothesizes that Taupo is at least partly to blame.

Kincaid explains that Taupo sits in the center of the North Island, so the eruptions may have isolated populations across the island, allowing their genes to evolve independently. The researchers ran simulations of different scenarios with different barriers that might have prevented mixing between populations. Most of the models suggested that the eruption was at least partially responsible. Kincaid notes that confirming this would require a time machine.

Kincaid answers the question of whether any kiwis live inside Taupo's caldera: there are none, because the caldera is now a lake. She notes that caldera lakes are not unusual, and cites Oregon's Crater Lake as another example.

The super eruption that helped create the Atitlán Caldera in Guatemala happened about 85,000 years ago. Since then the caldera has filled with water, and younger volcanic features have formed inside it, including a parasitic cone.

Kincaid explains that a parasitic cone is a secondary opening on the side of a main volcanic cone that allows lava to escape and build a separate small volcanic feature fed by the same magma. Brand new, larger volcanoes also formed inside the caldera, as they did at Aso. The tallest is the most active, erupting as recently as 1853.

Kincaid says every volcano in the video is still considered active by volcanologists, including those that have not erupted in thousands of years. She notes that the definition has changed over time and may vary between countries. According to the United States Geological Survey, a volcano is active if it has erupted within the past 11,700 years, which is the current Holocene epoch, or if it shows signs of unrest.

Those signs include earthquakes, volcanic gas emissions, or new magma lifting the floor of the volcano. Kincaid stresses that such activity does not have to be on a world-ending scale.

Kincaid turns to Mount Toba, which she says is probably the source of the misinformation that supereruptions always cause global mass extinctions. The Toba Catastrophe Hypothesis, proposed in 1998, suggested that the supereruption around 74,000 years ago triggered environmental collapse and pushed the human population almost to extinction. Kincaid says modern science has debunked most of that original hypothesis.

The hypothesis depends on a volcanic winter, in which ash and gases form aerosols in the atmosphere that reflect sunlight away from Earth's surface. Any large volcanic eruption can do this, and it can lower regional or global temperatures, affecting crops and causing food shortages. According to the original hypothesis, Toba's volcanic winter lasted as long as 10 years and its impacts as long as 1,000 years. Kincaid says that as volcanologists and archaeologists have studied the evidence, it has not supported those numbers. A supereruption did occur, but sediment from that time shows no hints of major long-term cooling.

Kincaid explains that an eruption with a much smaller VEI rating, or one that is not explosive enough to receive a VEI rating, could still produce a much worse volcanic winter if it releases much more sulfur. She says this is known from research on flood basalts, which produce almost no ash but put out large amounts of sulfur dioxide.

She concludes that studying large eruptions from so long ago is very difficult, and that understanding of these systems will keep changing as research technology improves. She says much inaccurate information circulates about supereruptions, and that the truth can be more interesting than what people invent. She adds that she is grateful we probably do not have to worry about supereruptions in our lifetime.