Supervolcanoes & Volcanic Winter
Describe supervolcanoes such as Yellowstone and Toba as volcanic centers that have had eruptions exceeding 1,000 cubic kilometers of material; explain how sulfur dioxide forms sulfate aerosols in the stratosphere that scatter sunlight and can cause volcanic winter; discuss the Toba catastrophe theory and how giant eruptions have interacted with ice ages; contrast supereruptions with ordinary eruptions in scale and climate impact
What a learner can do afterwards
- Describe a supervolcano as a volcanic center that has had a supereruption ejecting more than 1,000 cubic kilometers of material
- Explain how sulfur dioxide forms sulfate aerosols in the stratosphere, which scatter sunlight and can cool the planet
- Discuss the Toba catastrophe theory and uncertainty about its effects
1 · Read
Most eruptions affect a nearby region and are too small to change global climate. A large ordinary eruption might release about 1 cubic kilometer of ash and rock. A supereruption releases more than 1,000 cubic kilometers of material. A volcanic center that has had one is called a supervolcano. Toba in Indonesia released about 2,800 cubic kilometers. Such eruptions can leave a huge collapse crater called a caldera. Yellowstone and Toba have calderas left by past eruptions.
When Mount Pinatubo erupted in 1991, it pushed about 20 million tons of sulfur dioxide gas high into the stratosphere. That gas turned into tiny droplets called sulfate aerosols, which scattered sunlight back into space. Global temperatures dropped by about half a degree Celsius for a couple of years.
Most ash falls out within days or weeks. When an eruption sends enough sulfur dioxide into the stratosphere, it forms sulfate droplets that scatter sunlight. The droplets can linger and cool the planet for a few years, causing a volcanic winter. Eruptions that do not send enough sulfur dioxide that high may have little global cooling effect.
Toba erupted about 74,000 years ago, during a cold period of Earth's history. Some scientists think the ash and gas made that cold period even colder and nearly wiped out the small groups of early humans alive at the time. This idea is called the Toba catastrophe theory. Other scientists question how large the effect really was, and that disagreement is normal in science: a theory keeps getting tested against new evidence.
A supereruption ejects more than 1,000 cubic kilometers of material. Enough sulfur dioxide in the stratosphere turns into droplets that scatter sunlight and can cool the planet for years.
More to read
Unit 3: Yellowstone is active, but is it erupting?
Yellowstone National Park sits on top of a supervolcano. If it ever had a giant eruption, the effects could reach across much of the United States and Canada. But how likely is that to happen? In this unit, students act like real scientists. They look at earthquake data recorded over many decades and work out how often swarms of small earthquakes happen there. They also use GPS and satellite measurements to see whether the ground is rising or sinking, which can show if hot rock is moving underground. Finally, they explain what causes these earthquake swarms. The big lesson is that Yellowstone is active, with heat, quakes, and geysers, but being active is not the same as being about to erupt. Scientists watch it carefully, and right now the signs point to a volcano that is restless, not erupting.
The story of Lake Taupō
Not every giant volcano is a tall cone. Lake Taupo in New Zealand looks like a peaceful lake with a holiday town beside it, but it hides a supervolcano. About 25,500 years ago a massive eruption spat out so much magma that the ground fell in, leaving a caldera, a gigantic collapsed bowl about 30 kilometers across that later filled with water. Taupo is the most active supervolcano in the world, and scientists from many countries study it. Like Yellowstone, it shows that the biggest eruptions leave holes in the ground, not peaks.
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