The Volcano Explosivity Index (VEI) was designed by Chris Newhall, from the United States Geological Survey (USGS) and Stephen Self from the University of Hawaii back in 1982, and is a rough measure given to volcanoes to determine their explosiveness.
Scaling volcanic eruptions from the past in ways like this can help inform us of the risks involved with potential future volcanic eruptions, informing us of ways we need to prepare for these powerful geological phenomena. A higher VEI number indicates a stronger, more violent eruption, with an increased amount of total ejected material from the volcano at the time of eruption. The scale itself increases in value in powers of ten; volcanic eruptions in a particular VEI number releases ten times more volcanic material than eruptions in the number before it.
The 1992 eruption of Mt. Pinatubo, in the island of Luzon in the Philippines, was given a VEI of 6. The truly colossal eruptions, however, like the 1815 eruption of Mt. Tambora in Indonesia with a VEI of 7, and the last recorded eruption of the Yellowstone volcano 600,000 years ago with the highest VEI of 8, gave the two catastrophic events the name of “supereruption.” These supereruptions, then, spewed forth from some of the most powerful volcanoes in geological history: supervolcanoes.
Supereruptions have the capacity to change Earth’s climate, given the sheer amount of volcanic ash and other material that it can eject into the atmosphere during the event. These foreign material now in Earth’s atmosphere now have the capacity to block out the Sun, causing what is known as a “volcanic winter,” which can affect Earth for years after the eruption took place. The 1815 eruption of Tambora, for example, is the strongest volcanic eruption in recorded history; its eruption column affected global climate so much that the following year, 1816, was called “the Year Without a Summer.”
Now, scientists from Curtin University in Perth, Australia, studied the remnants of the caldera in Lake Toba, also in Indonesia, that last erupted some 75,000 years ago. The team, led by Associate Professor Martin Danišík from the John de Laeter Center based in Curtin University, found that the Toba supervolcano continued to spew out magma within the resulting caldera for up to 13,000 years after its supereruption; this, according to the team, should prompt scientists to rethink what it means for a volcano to be considered “eruptible.” The new study was published in the journal Communications Earth and Environment.
Danišík mentioned that magma continued to ooze out within the resulting caldera “[from] 5,000 to 13,000 years after the supereruption,” and that the resulting hard shell of magma that solidified on the caldera surface after the initial supereruption “pushed upward like a giant turtle shell.” They arrived at this conclusion using geochronological data, statistical inference and thermal modeling. They obtained data from the rock primarily by analyzing gaseous elements like argon (Ar) and helium (He). These gases accumulate inside minerals like zircon and feldspar, functioning like time capsules that show the properties of what its environment used to be like during the time when the rock solidified and trapped the gases inside.
“The findings challenged existing knowledge and studying of eruptions, which normally involves looking for liquid magma under a volcano to assess future hazard,” Danišík added. “We must now consider that eruptions can occur even if no liquid magma is found underneath a volcano — the concept of what is ‘eruptible’ needs to be re-evaluated.” The team also added that their results show that supervolcanoes don’t simply stop becoming a risk once they explode in such a violent manner, saying that these “post-eruption” events can persist for thousands of years.
Said Danišík: “Learning when and how eruptible magma accumulates, and in what state the magma is in before and after such eruptions, is critical for understanding supervolcanoes. […] Learning how supervolcanoes work is important for understanding the future threat of an inevitable super-eruption, which happen[s] about once every 17,000 years.”
References
- Curtin University. (2021, September 3). Threat of catastrophic supervolcano eruptions is ever-present. ScienceDaily. Retrieved September 23, 2021, from https://www.sciencedaily.com/releases/2021/09/210903085900.htm
- United States Geological Survey. (n.d.). VEi. United States Geological Survey. Retrieved September 23, 2021, from https://volcanoes.usgs.gov/vsc/glossary/vei.html
- United States Geological Survey. (n.d.). What is a supervolcano? What is a supereruption? United States Geological Survey. Retrieved September 23, 2021, from https://www.usgs.gov/faqs/what-a-supervolcano-what-a-supereruption?qt-news_science_products=0#qt-news_science_products
- Mucek, A. E., Danišík, M., de Silva, S. L., Miggins, D. P., Schmitt, A. K., Pratomo, I., Koppers, A., & Gillespie, J. (2021). Resurgence initiation and subsolidus eruption of cold carapace of warm magma at Toba Caldera, Sumatra. Communications Earth & Environment, 2(1), 1–9. https://doi.org/10.1038/s43247-021-00260-1
