ASU scientists develop technique using tiny crystal 'time capsules' to trace pulses of heat inside a volcano; may help better predict risk
Volcanos that erupt explosively are the most dangerous in the world. When they blow, they eject giant clouds of hot ash mixed with gases at temperatures up to 2,000 degrees Fahrenheit that engulf everything in their way.
A new technique developed by Arizona State University scientists, working with colleagues in California, Oregon, Michigan, Singapore and New Zealand, lets scientists track the heating history of the molten rock, or magma, that feeds explosive volcanos. The technique uses tiny crystals of zircon that form within the magma.
The picture coming from the new research, published June 16 in the journal Science, suggests that pulses of heat in the magma before a volcanic eruption both begin and end more abruptly than scientists previously thought. Moreover, the heat pulses last a shorter time than expected.
The new findings will change how scientists view the internal workings of all volcanos, and it may help them gain a better idea when an active volcano poses the most risk.
The team gathered debris that erupted from New Zealand's Mount Tarawera about 700 years ago. That eruption, roughly five times the size of the 1980 Mount St. Helens eruption, brought to the surface magma that recorded the volcano's thermal history, including the heat pulses leading up to the eruption.
Tiny bits tell a tale
The magma contained zircon crystals, each less than a millimeter long, which were the focus for the ASU scientists on the team.
"For the first time, we can tell how long ago a given zircon crystal formed — and we can also measure how many heat pulses it has experienced," said geochemist Christy Till, assistant professor in ASU's School of Earth and Space Exploration. She is a co-author of the Science paper.
"In addition," Till explained, "we can tell how hot those pulses were and how fast the crystals cooled after each of them." This lets geo-scientists build a detailed heat timetable of a volcano's past activity, including what occurred long before any historical records.
"We were especially interested in what events lead up to an eruption," Till said. "To our surprise, we discovered that these zircon crystals are telling us that they mostly led a very sedate, boring life."
The zircon crystals from Mount Tarawera had formed at least tens of thousands of years ago inside the volcano, as molten rock cooled, Till said. "Over their lifespan, they experienced only a few brief heating events, whereas we had expected to see more prolonged pulses of heating."