Supervolcanoes & Volcanic Winter
Describe calderas such as Yellowstone and Toba as supervolcanoes capable of erupting thousands of cubic kilometres of ash; explain how sulphur dioxide aerosols in the stratosphere scatter sunlight and cause volcanic winter; discuss the Toba catastrophe theory and how giant eruptions have interacted with ice ages; contrast supervolcano eruptions with ordinary eruptions in scale and climate impact
The lesson
Think about the volcanoes you've studied so far: lava flows and ash clouds that affect a nearby region. A supervolcano is far bigger. It can blast out thousands of cubic kilometers of ash and rock in a single eruption. The huge crater left behind is called a caldera. Yellowstone in the United States and Toba in Indonesia both sit inside calderas made by past supervolcano eruptions.
When Mount Pinatubo erupted in 1991, it pushed 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. A supervolcano releases thousands of times more sulfur dioxide, so the cooling it causes, known as a volcanic winter, can be far stronger and last for years.
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 put huge stress on early human groups. 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 supervolcano can eject thousands of cubic kilometers of ash and gas, and the sulfur dioxide it releases can scatter sunlight and cool the planet for years.
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