The eruption of the Toba supervolcano in Indonesia, around 74,000 years ago, ejected billions of tonnes of dust and sulphates into the atmosphere. Experts estimate that it caused a global cooling of 3-5°C for several years, and led to devastating loss of plant and animal life. Some have argued that Toba caused the greatest mass extinction in human history, bringing our species to the brink of extinction. Super-volcanic eruptions are events in which at least 500 km3 of bulk material is expelled. Eruptions of such magnitude may happen at any time in the future, with catastrophic consequences.
In order to assess the likelihood of supervolcanic eruptions, we have to rely on a relatively limited set of past observations, which makes any estimates very uncertain. Existing data suggest that a supervolcanic eruption will occur every 30,000- 50,000 years on average – with the last known event occurring 25,000 years ago in New Zealand. We are currently unable to anticipate volcanic eruptions beyond a few weeks or months in advance, but scientists are monitoring a number of areas, including Yellowstone in the US, which have been identified as potential sites of a future supervolcanic eruption.
The impact of a supervolcanic eruption is directly connected to the quantities of materials ejected by the volcano. Dust and ashes will kill human populations nearby and devastate local agricultural activity. In addition, the release of sulphate and ashes in the atmosphere will affect the amount of solar energy reaching the surface of the planet and may lead to temporary global cooling and severe environmental effects.
We are currently unable to anticipate volcanic eruptions beyond a few weeks or months in advance.
Volcanic eruptions are measured through a magnitude scale, a logarithmic scale, ranging from 0 to 8, where each unit increase indicates an eruption 10 times greater in erupted mass. 0 means a release of less than 10,000 m3 of magma. At the top of the scale, supervolcanic eruptions (M 8) release more than 500 km3 of magma. By comparison, the largest volcano eruption recorded in human history, the 1815 Tambora eruption in Indonesia, was a magnitude of 6: 41km3 of magma was expelled, claiming over 70,000 lives. When Mount Vesuvius erupted in 79 AD, devastating the Roman cities of Pompeii and Herculaneum, it released approximately 4km3 of magma, placing it at magnitude 5. More recently, the May 1980 eruption of Mount St. Helens in Washington, USA, with just over 0.5km3 released, was a magnitude 5.1.
Professor, School of Earth Sciences, University of Bristol