To figure out where magma gathers in the earth’s crust and for how long, volcanologist Guilherme Gualda and his students traveled to the planet’s most active cluster, the Taupo Volcanic Zone of New Zealand, where some of the biggest eruptions of the last 2 million years occurred — seven in a period between 350,000 and 240,000 years ago.
The aim of the project was to better understand how the systems of magma – molten or semi-molten rock -that feed them are built and how the Earth reacts to repeated input of magma over short periods of time.
After studying layers of pumice visible in road cuts and other outcrops, measuring the amount of crystals in the samples and using thermodynamic models, they determined that magma moved closer to the surface with each successive eruption.
Gualda is associate professor of earth and environmental sciences at Vanderbilt University and first author of the study published October 10, 2018, in the peer-reviewed journal Science Advances. He said in a statement:
As the system resets, the deposits become shallower. The crust is getting warmer and weaker, so magma can lodge itself at shallower levels.
What’s more, the study suggests, the dynamic nature of the Taupo Volcanic Zone’s crust made it more likely for the magma to erupt than to be stored in the crust. The more frequent, smaller eruptions, which each produced 12-36 cubic miles (50-150 cubic km) of magma, likely prevented a supereruption. Supereruptions produce more than 108 cubic miles (450 cubic km) of magma, and they affect the earth’s climate for years following the eruption. Gualda said:
You have magma sitting there that’s crystal-poor, melt-rich for few decades, maybe 100 years, and then it erupts. Then another magma body is established, but we don’t know how gradually that body assembles. It’s a period in which you’re increasing the amount of melt in the crust.
The question that remains is how long it took for these crystal-rich magma bodies to assemble between eruptions. It could be thousands of years, Gualda said, but he believes it’s shorter than that.
Bottom line: To figure out where magma gathers in Earth’s crust and for how long, researchers traveled to the planet’s most active cluster: the Taupo Volcanic Zone of New Zealand, site of some of the biggest eruptions of the last 2 million years.