Recent discoveries from Iceland’s Fagradalsfjall eruptions have changed what we know about how volcanoes work.
Led by Saemundur Halldorsson at the University of Iceland, a team of geologists were trying to find out “how deep in the mantle the magma originated, how far beneath the surface it was stored before the eruption, and what was happening in the reservoir both before and during the eruption.”
“The assumption was that a magma chamber fills up slowly over time, and the magma becomes well mixed,” explained Matthew Jackson, from the University of California. As a result of this well established two-step process, he added, those studying volcanic eruptions do not expect to see significant changes in the chemical composition of the magma as it flows out of the earth.
“This is what we see at Mount Kīlauea, in Hawaii,” Jackson said. “You’ll have eruptions that go on for years, and there will be minor changes over time.”
“But in Iceland, there was more than a factor of 1,000 higher rates of change for key chemical indicators,” Jackson said. “In a month, the Fagradalsfjall eruption showed more compositional variability than the Kīlauea eruptions showed in decades. The total range of chemical compositions that were sampled at this eruption over the course of the first-month span the entire range that has ever erupted in southwest Iceland in the last 10,000 years.”
According to the scientists, this variability is a result of subsequent batches of magma flowing into the chamber from deeper in the mantle.
“Picture a lava lamp in your mind,” said Jackson. “You have a hot lightbulb at the bottom, it heats up a blob and the blob rises, cools, and then sinks. We can think of the Earth’s mantle — from the top of the core to under the tectonic plates — operating much like a lava lamp.” He explained that as the heat causes regions of the mantle to rise and plumes form and move buoyantly upward toward the surface, molten rock from these plumes accumulates in chambers and crystallizes, gases escape through the crust, and the pressure builds until the magma finds a way to escape.
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