Geologists studying the dormant supervolcano Toba on the island of Sumatra in Indonesia have found signs that magma continues to accumulate in its depths. This is evidenced by the slow rise of the solidified lava dome in the volcano's caldera. The research results are published in the journal Communications Earth & Environment.
The eruption of any of the supervolcanoes, of which there are currently about two dozen on Earth, can not only provoke global climate change, but also become catastrophic for all living things. Therefore, scientists are trying to understand as much as possible the mechanisms that lead to the formation of huge volumes of molten magma under supervolcanoes.
The results of experiments and numerical simulations show that eruptions of supervolcanoes occur due to the rise of liquid magma through the earth's crust - when it rises from a depth of more than ten kilometers, its sharp expansion occurs, leading to an explosion and a catastrophic eruption.
Scientists use geophysical instruments to monitor the state of the bowels under supervolcanoes so as not to miss the moment when liquid magma begins to rise, which, according to geological data, occurs once every several tens of thousands of years.
Researchers from the USA, Germany, Australia and Indonesia studied the composition of the frozen magma of the supervolcano Toba and determined the age of the layers of volcanic rocks from the isotopic composition of argon and helium in minerals - feldspar and zircon.
The authors found that large eruptions occurred at intervals of about 17 thousand years, but between them the volcano retained some activity. These data challenged the generally accepted theory that supervolcanoes are not dangerous between episodes of large eruptions.
"Understanding what happens during these extended periods of dormancy will help us predict future eruptions of young, active supervolcanoes," said one of the study's authors, associate professor Martin Danišík, in a press release from the Australian Curtin University.
Using geochronological data and thermal modeling, the authors proved that for five to thirteen thousand years after each major eruption of the Toba volcano, magma continued to slowly flow into the volcano's caldera, gradually lifting the frozen layers of lava like a giant tortoise shell.
"The data we have obtained force us to rethink existing knowledge and methods of studying supervolcanoes, which usually include searching for liquid magma under them to assess future hazards. Now we must take into account that eruptions can occur even if there is no chamber of liquid magma under the volcano," says Danishik "Our results show that the danger does not disappear with a super-eruption, and the threat of new threats persists many thousands of years later."
The authors note that it is not the presence of magma under the supervolcano itself that is of decisive importance for understanding the risks of new eruptions, but its state, the rate of accumulation and dynamics of propagation in the earth's crust.