. . . 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." As the heat causes regions of the mantle to rise and plumes form and move buoyantly upward toward the surface, he explained, 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.
For the first few weeks, as described in the paper, what erupted was the expected "depleted" magma type that had been accumulating in the reservoir, located about 10 miles (16 km) below the surface. But by April, evidence showed that the chamber was being recharged by deeper, "enriched" type melts with a different composition that were sourced from a different region of the upwelling mantle plume beneath Iceland. This new magma had a less modified chemical composition, with a higher magnesium content and a higher proportion of carbon dioxide gas, indicating that fewer gases from this deeper magma had escaped. By May, the magma that dominated the flow was the deeper, enriched type. These rapid, extreme changes in
magma composition at a plume-fed hotspot, they say, "have never before been observed in near real-time."
These changes in composition may not be so rare, Jackson said; it's just that opportunities to sample eruptions at such an early stage are not common. For example, prior to the 2021 Fagradalsfjall eruption, the most recent eruptions on Iceland's Reykjanes peninsula occurred eight centuries ago. He suspects that this new activity signal the start of a new, possibly centuries-long volcanic cycle in southwest Iceland.
