The mysterious side of volcanic eruptions was first observed • Earth.com

A team of researchers led by Dr University of California, Santa Barbara Volcanologists have discovered a much more dynamic process than volcanologists had assumed possible in the two centuries they were studying volcanic events. Experts made the discovery while sampling magma from the Fagradalsfjall volcano in Iceland, which erupted in March 2021.

By trying to explain how deep magma originated in the mantle, how much was stored below the surface before the eruption, and what was happening in the reservoir before and during the eruption, the researchers got a “big surprise”—as study co-author Matthew Jackson put it.

“The assumption was that the magma chamber slowly fills up over time, and that the magma mixes well. And then it drains over the course of the eruption.”

According to Jackson (and most other volcanologists), as a result of this well-defined two-step process, there are usually no significant changes in the chemical composition of magma as it flows out of the Earth.

“This is what we see at Mount Kolawea in Hawaii,” Jackson said. “You’re going to have a volcanic eruption that lasts for years, and there will be subtle changes over time.

But in Iceland, there were more than 1,000 factors with higher rates of change for the main chemical indicators. Within a month, the Fagradalsfjall eruption showed more compositional variance than the Kīlauea eruption had shown in decades. The total range of chemical compositions sampled in this eruption over the course of the first month spans the entire range that erupted in southwest Iceland in the last 10,000 years.”

Experts said this extreme contrast is likely due to later batches of magma flowing into the chamber from the deeper layers of the mantle. “Imagine a lava lamp in your mind. You have a hot lamp at the bottom, it heats up a point and the point rises and cools and then sinks. We can think of the Earth’s mantle—from the top of the core to the bottom of the tectonic plates—working like a lava lamp,” Jackson explained.

As heat causes some areas of the mantle to rise, form plumes, and move upward toward the surface, molten rock accumulates in chambers and crystallizes, gases escape through the crust, and pressure builds up allowing magma to eventually erupt. In the case of the Fagradalsfjall volcano, although the first eruption was the expected “depleted” type of magma accumulating in the reservoir, in about a month the chamber was recharged with a deeper “fertilized” type of melt with a different composition (higher magnesium and carbon dioxide levels). In another month, the magma that controlled the flow was of the deepest and richest type.

Although such rapid and extreme changes in magma composition have not been observed before – likely due to the fact that chances of sampling eruptions at such an early stage are not uncommon – they may not be so rare. More research is needed to assess the frequency of such phenomena in other volcanic eruptions, and to elucidate the mysterious ways in which volcanoes operate.

The study was published in the journal temper nature.

by Andrei IonescuAnd the Earth.com crew clerk