SAN FRANCISCO, June 16 (Xinhua) -- By analyzing crystals of the mineral zircon, zirconium silicate, in magma from an eruption in the Taupo Volcanic Zone in New Zealand about 700 years ago, researchers are able to determine the magma's history and better understand when a volcano is heading toward an eruptive phase.
The analysis shows the magma went through a comparatively "cool" period for thousands of years before heating up. Once magma temperatures reached 750 degrees Celsius, it was a short amount of time - decades or less - before an eruption occurred.
"Mobility in magma is a function of temperature and most of the time when it's sitting there in the Earth's crust under the volcano, it's cool," noted Adam Kent, an Oregon State University (OSU) geologist and co-author on the study published this week in the journal Science. "Of course, cool is a relative description since it's still some 650 degrees (Celsius). I wouldn't put my finger on it."
Noting that the Taupo magma system has similarities to many volcanoes around the world, Kent explained that "to erupt onto the Earth's surface, magma needs to heat up so it can be runny enough to be squeezed along cracks in the Earth and pushed up to the surface. At lower temperatures, the magma is too crystal-rich and viscous to move. It's like trying to spread cold peanut butter onto a piece of bread. It takes higher temperatures to get things moving - and then our data show it's only a period of years or decades before it erupts."
The key to honing in on the long-term geologic processes is understanding the volcanoes' thermal or temperature history, according to Kent and his colleagues. Past studies began making inroads into understanding the history of magma temperatures, but they relied on trying to reconcile data from a sample containing many thousands of individual crystals.
Using zircon crystals, which can be dated through analyzing the decay of uranium and thorium, adds more resolution, or precision, to the process. The crystals are like a "black box" flight recorder for studying volcanic eruptions, Kari Cooper of the University of California, Davis, corresponding author on the study, was quoted as saying in a news release from OSU. "Instead of trying to piece together what happened from the wreckage, the crystals can tell us what was going on while they were below the surface, including the runup to an eruption."
In addition, the finding suggests that if many volcanoes store their magma in this relatively cold state, recognizing volcanoes where warm and mobile magma is present may help researchers find volcanoes in the early throes of producing future eruptions. The technology to monitor volcanoes using seismic waves and other remote techniques is improving all the time, the researchers said.