Magma reservoirs more similar to snow cone than vat of boiling lava

KARI COOPER / COURTESY

New tools allow for accurate analyses of subsurface systems

Kari Cooper, a professor in the Earth and Planetary Sciences Department at UC Davis, is researching what happens underneath a volcano through indirect examinations.

Cooper’s research group studied post-eruption volcanoes in New Zealand, the most recent of which was about 200 years old, which is considered relatively young. This type of analyses combined two different sets of data which hadn’t been put together with this volcanic crystal before.

“These crystals are called zircon,” Cooper said. “They’re one of the primary ways that we can determine the age of a magma. The crystals just happen to have the right chemical composition that we can date them using radiometric data. For that reason, they’re an important archive of what’s going on. This is something that we just did in the last couple of years that’s culminated in this publication [released June 15] — being able to do this in this particular type of crystal — not the dating itself, as that’s been around a long time, but connecting that to the temperature information. This combination of age information and temperature information within volcanic crystals that particular combination started with our work in 2014. It’s been in recent years that we’ve been able to connect these two pieces of information about the subsystem.”

Other crystals had been used in previous research, but Cooper’s group is the first to be able to closely examine zircon crystals specifically. Most laboratories do not have the necessary equipment to synthesize and analyze such tiny materials. Adam Kent, a professor in the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University and a co-author of the paper, published in Science, stated that there are only a few people capable of doing these analyses.

“Especially with what [Cooper] does, there’s only a handful of people in the world who are set up to do that and know how to do it,” Kent said. “So, we’ve probably had [this research] mostly to ourselves. The zircon technique, again, you need a specialized piece of equipment, like a five million dollar thing called an ion probe.”

Through a complex series of actions and with specialized equipment, the researchers can obtain a profile of the chemical variation derived from different parts of the zircon crystals. What is even more impressive is that the zircons are each 100 micrometers long, which is about the width of a single human hair.

“We decided to look at zircon because it is a common ‘accessory’ mineral,” said Allison Rubin, the lead author and a graduate student of Cooper’s. “It’s not present in very large abundances, but it does have a tendency to ‘suck up’ these elements that don’t go into any other crystals. So we can use them to date them and trace where they come from — like if they come from the mantle or the crust of the earth. Basically, zircons are unique in that they can be used in ways most other minerals can’t, to preserve the information about the melt in which they were formed.”

Magma reservoirs are completely different than the popular Hollywood view of a boiling hot vat of lava underneath a volcano. One of the analogies of volcanic magma is that it’s like a snow cone — mostly solid, with some liquid running through it.

“The emerging view of magma is actually that it’s not a liquid like water, it’s more complicated — it’s a mixture of solids and liquids,” Kent said. “It contains a lot of crystals. If you have a lot of crystals, more than about 50 percent, the magma can’t go inward. Basically, [it] stays as a solid rock. As you get more liquid, if you get more than about half as liquid, you can actually make it flow.”

If the liquid-solid percentage exceeds a certain point, an eruption may occur.

“You can do a couple different things to trigger an eruption,” Rubin said. “You can increase the heat in the system. For example, you can have a hotter body of magma come up from underneath and increase the temperature in the system, generate a lot of melt and cause an eruption that way. You can decrease the pressure, so that magma rises up through the crust. There is a thermodynamic point that will cause it to rise and it will start to erupt. Essentially, if you end up with a body of melt that is saturated, which we call volatiles, which are dissolved liquids and gases, it’s like shaking a bottle of soda. The volatiles in the magma can trigger an eruption that way.”

One of the study’s more surprising developments was finding proof that magma was relatively cold, something that other researchers had theorized but had never really found solid evidence for.

“This is the first time we’ve been able to actually put numbers on this,” Rubin said. “For example, people have previously said, ‘we think magma chambers or reservoirs have been spending long periods of time at low temperatures and short periods of time at high temperatures’, and this is the first direct evidence we’ve seen that is happening, and the first numbers we’ve been able to put on it. We can say, ‘Okay likely only a couple percent of its lifetime was spent at high temperatures and over 95 or 96% of its time, it’s spent at low temperatures.’”

Not only does this research create new tools for future work, but there are also practical and real-world applications.

“We are, in theory, capable of forecasting volcanic eruptions at a similar level that we can forecast weather, but we need a lot more information,” Cooper said. “We need an idea of what’s going on below the surface in order to interpret all of these monitoring signals in order to understand what they mean in terms of what’s happening below the surface. What my work does is provide more information about how we think about what happens below the surface and how that connects to the monitoring of hazards.”

Cooper also stated that, at any time, there are anywhere from 10 to 20 volcanic eruptions happening in the world.

“As we discovered in the Iceland eruption in 2010, that disrupted air traffic over most of Europe for weeks and that was a very small eruption,” Cooper said. “You don’t have to live near a volcano for volcanic eruptions to disrupt you. This is not an uncommon phenomenon globally. The chances are that sometime in your lifetime, you will be affected indirectly or directly by a volcanic eruption.”

So far, Cooper has received support and compliments from some of her fellow researchers, but she expects that there will be groups that that will come up with rebuttals in the next few years.

“I think that one of the important things in this paper is that it’s going to stimulate a lot of discussion,” Cooper said. “There are going to be a lot of people who agree with parts of it, disagree with other parts of it, or disagree with it all. It’ll be part of the overall scientific conversation, so I’m curious to see how people are reacting to it.”

 

Written by: Jack Carrillo Concordia — science@theaggie.org