Science & Technology

Life after a super eruption-Eos

Lake Toba on the island of Sumatra, Indonesia, is the largest volcanic lake in the world as a result of the youngest Toba tuff eruption that occurred 74,000 years ago. And it was big, even a super-eruption.

“Area of ​​about 100 km around Toba [any] The direction was completely ash-filled. ” Shana Kadesilva, Professor of Oregon State University. “Then the ash went to the sea on either side, and it went up to the atmosphere and then produced a plume of these large ash distributed to the region.”

But that wasn’t the only thing. Decilva was part of a new study that discovered that there was life after a super-eruption.By studying ResurrectionDuring a poorly understood period of post-supervolcano recovery, researchers found that the Toba system caused thousands of small eruptions during the thousands of years after the supervolcano, even in the absence of hot magma at the volcano. discovered. This meant that these small volcanoes were erupting with semi-solid material that had been refrigerated, and the revival period of the volcanic system was much longer than previously thought. NS study Was published in Communication Earth and environment.

Finesse dating

Shanaka de Silva and other volcanologists conducted fieldwork on Lake Toba between 2012 and 2016. Credit: Adonara Mucek

Earlier dating showed that catastrophic and small eruptions were of the same age, according to DeSilva, but geological evidence does not. The problem was that traditional argon-argon dating was not accurate enough to measure small (geologically) time differences.

To get a more accurate age, researchers used new technology in volcanology Uranium-Thorium-Helium Thermal Chronology About feldspar and zircon samples collected in Toba. They found that helium in samples from smaller eruptions was up to 13,000 years younger than the Argon-Argon age. The cold solid material produced by these small eruptions solidified at the top of the magma chamber, rather than liquid magma, and was stored at 180 ° C to 500 ° C for 5,000 to 13,000 years. Magma is liquid at about 700 ° C.

“The really exciting part is the thermochronological approach that is usually applied to plate tectonics and the like. [applied to] To volcanology, “said DeSilva. “It really shows that modern geochronological techniques can provide insights into temperature ranges that are not available with the usual research techniques in use.”

Cold (er) storage

Patricia GregAn associate professor of geophysics at the University of Illinois at Urbana-Champaign, who was not involved in the study, this is a compelling and well-made study that could reconsider which substances are considered eruptible. Said there is. The most important aspect of the study is how cold the volcano is.

“After a lot of material was expelled from the magma system, it sat there and cooled, and what was really left was this crystal-rich group, which you didn’t expect to erupt. bottom.”

“I think it’s really wild, because in my mind and in the minds of many, we think that this kind of magma will constantly flow into the system,” she said. “But now there is this very big eruption, a large amount of matter is expelled from the magma system, sitting there and cooling. And really, what is left is expecting you to erupt. No, it was a group rich in this crystal. “

Others claim that these systems are much cooler than previously thought, Greg added. This study “is like being in line with other studies. Interesting paper It has come out in the last few years, “she said.

Other volcanic sites support the idea that erupting magma does not need to be hot to move. “We are currently finding evidence that solid matter can actually erupt on Mount St. Helens and several other places,” de Silva said.

However, according to de Silva, these magma systems are not truly warm or cold because they exist in different temperature ranges. “You have a cold part of the magma chamber, and then you have a warm part of the magma chamber,” he said.

Greg said the follow-up should include why the crystal-rich viscous magma erupted. “I think that’s a question for modelers like me. How do you get something like this mechanically? Here’s the evidence that something like this comes out. It’s very cold and very Is viscous and very crystalline. How did it erupt? “Greg asked.

DeSilva and his fellow researchers plan to expand their work in Toba to explore more areas and better understand the time frame of a catastrophic eruption. About 100,000 people live on Samosir Island, a large island on Lake Toba, and it is a revived dome. Push up..Mount Sinabung, a former nearby volcano research The proposal is part of the Toba system, which began erupting in 2010 and has been active ever since. (The latest eruption stage began with July.. )

“The information we have is useful in understanding how the supervolcano cycle actually works,” said DeSilva.

— Daniel Bruto (@daniellebeurt), Science writer

Quote: Beurteaux, D. (2021), Life after the super eruption, Eos, 102, Published on October 27, 2021.
Text © 2021. author. CC BY-NC-ND 3.0
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Life after a super eruption-Eos Life after a super eruption-Eos

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