Volcanic eruptions are unpredictable, but these geologists cracked the code

Volcanic eruptions are unpredictable, but these geologists cracked the code thumbnail

Volcanic eruptions can be unpredictable.

On June 26, 2018, the earth rumbled under the giant sleeping tortoises on Isabela Island in the Galapagos. Soon after, , the volcano that towers above the island, was erupting . Over the next two months, the volcano’s fissures spewed out enough lava to cover an area of roughly 19 square miles.

This was not the first eruption of Sierra Negra: It has been blown at least seven times in the last century. But what made the 2018 phenomenon special is that geologists had forecasted the eruption’s date as early as January. They almost got it right down to the exact day.

It was a lucky forecast, to be certain. It was a fortunate forecast, to be sure. Sierra Negra is just one volcano in a sparsely inhabited archipelago, but when hundreds of millions of people around the world reside in volcanic danger zones, translating these forecasts to other craters could save untold numbers of lives.

[Related: A 1930s adventure inside an active volcano]

“There is still a lot of work to be done, but … volcano forecasting may become a reality in the coming decades,” says Patricia Gregg, a geologist at the University of Illinois Urbana-Champaign and one of the paper’s authors.

Forecasting eruptions is like forecasting the weather. It is difficult to accurately predict the future with so many variables and moving parts. A forecast for tomorrow might be reliable, but a forecast for the next week might not.

This made Gregg’s and her colleagues’ Sierra Negra forecast, which was made five months before the eruption, all the more valuable. The volcano had already begun to roar by that time, with high levels of seismic activity. However, forecasters agree it was a gamble.

” It was always meant to be a test,” states Gregg. “We did not put much faith in our forecast being accurate.”

But Sierra Negra is a great laboratory for fine-tuning volcanic predictions. Because it erupts once every 15 or 20 years, it gets a lot of scrutiny, with scientists from both Ecuador and around the world continually monitoring it. By 2017, their instruments were picking up renewed rumblings indicating a future eruption.

[Related: How to study a volcano when it destroys your lab]

Experts are aware that volcanoes such as Sierra Negra can burst their tops when magma builds in the reservoir below. The earth is constantly under increasing pressure as more magma presses against the rock. Something has to give eventually. The rocks begin to break and magma starts to burst. Geologists could predict when the breaking point would occur if they knew how the rocks break down.

Gregg, along with colleagues, used methods that are familiar to weather and climate forecasters. They combined observational data about the volcano’s activity with predictions from simulations. To see what the bloating magma reservoir was doing beneath Sierra Negra, they used satellite radar images and ran models on supercomputers.

Based on how the magma was inflating by January 2018, their forecasts highlighted a likely eruption between June 25 and July 5. The levels kept rising at the same rate over the next few months–and the eruption began on June 26, right on schedule.

” If anything had changed in those months, our forecast wouldn’t have worked,” Gregg says.

“The very tight coincidence of the author’s forecast with the eruption onset must involve some good fortune, but that in itself tells us something,” says Andrew Bell, a geologist at the University of Edinburgh, who has studied Sierra Negra but wasn’t an author on the paper.

Colorful rocks on the Sierra Negra volcano in the Galapagos
The Sierra Negra volcano seemingly at rest. Deposit Photos

In the years that followed, Gregg and her colleagues looked back at their calculations to see what they had done wrong–and what “something” might have been. To see if they could come close to reality, they ran more simulations with data from the actual eruption.

What they found was that the magma buildup remained relatively constant over the first part of 2018. Late June saw enough pressure build up against the volcano’s bottom to trigger a moderately powerful earthquake. This seemed to be the last straw, cracking the rock and allowing the magma to flow through.

This practice of simulating historic phenomena to check the accuracy of forecast models is sometimes called “hindcasting” in meteorology. In addition to Sierra Negra, Gregg and her colleagues have examined old eruptions from Sumatra, Alaska, and underwater off the coast of Cascadia.

[Related: Tonga’s historic volcanic eruption could help predict when tsunamis strike land]

Is it possible to use the exact same forecasting techniques in different parts of the world? Geologists must adjust their models to account for the unique characteristics of each volcano. The Sierra Negra study authors discovered some commonalities in ground motions and eruption probabilities.

Better forecasting models allow scientists to learn more about the physical processes that make volcanoes rumble to life. They also help to match simulations to actual-world conditions. Bell states that it is difficult to make accurate forecasts prior to an event taking place. However, it is important to try .”

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