A new study has found that the rare but spectacular eruptions of supervolcanoes can cause massive destruction and affect climate patterns on a global scale for decades.
In addition, the supereruption sites may experience ongoing, albeit smaller eruptions for tens of thousands of years after.
In the study published this week in the journal Nature Communications, Oregon State University (OSU) researchers said they were able to link recent eruptions at Mt. Sinabung in northern Sumatra, Indonesia, to the last eruption on Earth of a supervolcano 74,000 years ago at the Toba Caldera some 40 kilometers, or 25 miles, away.
This is the first time that researchers have been able to pinpoint what happens following the eruption of a supervolcano. To qualify as a supervolcano, the eruption must reach at least magnitude 8 on the Volcano Explosivity Index, which means the measured deposits for that eruption are greater than 1,000 cubic kilometers, or 240 cubic miles.
When Toba erupted, it emitted a volume of magma 28,000 times greater than that of the 1980 eruption of Mount St. Helens in Washington state of the U.S. Pacific Northwest. It was so massive, it is thought to have created a volcanic winter on Earth lasting years, and possibly triggering a bottleneck in human evolution. Other well-known supervolcano sites include Yellowstone Park in the United States, Taupo Caldera in New Zealand and Campi Flegrei in Italy.
"The recovery from a supervolcanic eruption is a long process, as the volcano and the magmatic system try to re-establish equilibrium -- like a body of water that has been disrupted by a rock being dropped into it," said Adonara Mucek, an OSU doctoral candidate and lead author on the study. "At Toba, it appears that the eruptions continued for at least 15,000 to 20,000 years after the supereruption and the structural adjustment continued at least until a few centuries ago, and probably is continuing today. It is the magmatic equivalent to aftershocks following an earthquake."
Previous argon dating studies had provided rough ages of eruptions at Toba, but those eruption dates had too much range of error. In their study, the OSU researchers and their colleagues from Australia, Germany and Indonesia were able to decipher the most recent volcanic history of Toba by measuring the amount of helium remaining in zircon crystals in erupted pumice and lava.
A remnant of the decaying process of uranium, the helium remaining in the crystals has a well-understood radioactive decay path and half-life.
"Toba is at least 1.3 million years old, its supereruption took place about 74,000 years ago, and it had at least six definitive eruptions after that and probably several more," Mucek was quoted as saying in a news release from OSU. "The last eruption we have detected occurred about 56,000 years ago, but there are other eruptions that remain to be studied."
The researchers also managed to estimate the history of structural adjustment at Toba using carbon-14 dating of lake sediment that has been uplifted up to 600 meters above the lake in which they formed, indicating that the structural adjustment continued from at least 30,000 years ago until 2,000 years ago and may be continuing today.
The study also found that the magma in Toba's system has an identical chemical fingerprint and zircon crystallization history to Mt. Sinabung, which is currently erupting and is distinct from other volcanoes in Sumatra. This suggests that the Toba system may be larger and more widespread than previously thought, said Shanaka "Shan" de Silva, an OSU volcanologist and co-author on the study. "Our data suggest that the recent and ongoing eruptions of Mt. Sinabung are part of the Toba system's recovery process from the supereruption."
The discovery of the connection does not suggest that the Toba Caldera is in danger of erupting on a catastrophic scale any time soon, the researchers noted. "This is probably 'business as usual' for a recovering supervolcano," de Silva said.
"Supervolcanoes have lifetimes of millions of years during which there can be several supereruptions," said de Silva. "Between those eruptions, they don't die. Scientists have long suspected that eruptions continue after the initial eruption, but this is the first time we've been able to put accurate ages with those eruptions."