(CN) – Crystals from the inside of a volcano are helping researchers gain insight into magma reservoirs that lie below volcanoes, which send signals of impending eruptions up to centuries before they occur.
Publishing their findings in the current issue of the journal Science, the team presents a new view of how volcanoes work, which can help scientists identify potential eruptions.
“To understand volcanic eruptions, we need to be able to decipher signals the volcano gives us before it erupts,” said Jennifer Wade, a program director at the National Science Foundation, which funded the research. “This study backs up the clock to the time before an eruption, and uses signals in crystals to understand when magma goes from being stored to being mobilized for an eruption.”
Studying magma directly is challenging as heat and pressure destroy any instruments placed into it, and reservoirs typically lie miles beneath the Earth’s surface, making it difficult for researchers to learn about the underlying components of volcanoes.
“Our concept of what a magma reservoir looks like has to change,” said co-author Kari Cooper, a geoscientist at the University of California, Davis.
The team studied magma by collecting zircon crystals from debris deposited around Mount Tarawera in New Zealand after it erupted about 700 years ago – which might have contributed to the Great Famine of 1315 in Europe.
That eruption – about five times the size of Mount St. Helens in 1980 – forced long-buried lava to the surface from the magma reservoir below. Once it reached the surface, the lava’s chemistry and temperature history provided a clear record of its past, functioning like a ”black box” flight recorder for studying volcanic eruptions, Cooper said.
“Instead of trying to piece together the wreckage, the crystals can tell us what was going on while they were below the surface, including the run-up to an eruption,” she said.
By analyzing trace elements in seven zircon crystals at the site, the team determined when the crystals formed and how long they were exposed to heat in excess of 1,292 degrees Fahrenheit. The scientists were also able to collect information about where the crystals resided within the magma reservoir.
The team found that all but one of the crystals were at least tens of thousands of years old, but had only been exposed to molten magma for less than 4 percent of that time.
Cooper described the emerging picture as less a bubbling mass of molten rock than something like a snow cone – mostly solid and crystalline, with some liquid seeping through it.
An eruption is triggered when a certain amount of solid, crystalline magma has to melt and mobilize, such as by interacting with hotter liquid from elsewhere in the reservoir.
The researchers believe that pre-eruption magma likely absorbs material from different parts of the reservoir, a process that takes places over decades or centuries. This fairly brief process – at least by geologic time – suggests that scientists could identify potential eruptions by looking for volcanoes with the most mobile magma.
The crystals remained solid in Mount Tarawera’s magma reservoir through an eruption that happened about 25,000 years ago, before being exhaled in the smaller eruption 700 years ago.