“Some have thoughts that the systems are linked at depth,” says Edward Marshall, a geochemist at the University of Iceland—either directly, with magma flowing between the two subterranean mazes, or indirectly, where they trade pressure. But any geologic connection between Fagradalsfjall and Svartsengi is tenuous at best, making understanding why magma ascends at the former several times, then switches to the latter, a tall order.
This investigative effort is further complicated by the current crisis’s additional idiosyncrasies. Over the past few years, Thorbjörn—a volcanic mound close to the Svartsengi geothermal power station and Grindavík—has occasionally inflated, perhaps due to the movement of magma somewhere below, but this has always ended without incident. The events of the past week “certainly mark a break in that pattern,” says Tom Winder, a volcano seismologist at the University of Cambridge.
Initial estimates hint that the amount of magma involved is more substantial than the peninsula’s past three eruptions, and it also flowed into the Svartsengi area at an astonishing speed. “Why the magma inflow rate appears to be so much higher this time, and indeed where it was sourced from, remains an important open question,” says Winder. Considering the seemingly hefty volume of magma, the potential for a long-lived eruption, or an otherwise very prolific eruption of lava, is high—but paradoxically, as with many eruptions, it could be that only a fraction of that molten rock sees daylight.
That the magma hurriedly rose toward Grindavík late last week, then paused just beneath its now-empty streets, has engendered both curiosity and anxiety. The reasons for this interlude are not quite clear. During the 2021 eruption, there was a three-week gap between the magmatic curtain invading the shallow subsurface and the emergence of the eruption itself. The same may transpire this time. Or it may erupt after you finish reading this article—there is no surefire way to know.
That there will even be an eruption isn’t certain. Presently, based on the proximity of the magma to the surface and the constant seismic rumbling, Iceland’s Meteorological Office suspects that there is a very high likelihood of an eruption, somewhere along that 10-mile-long line of deformed and quaking ground, in the coming days. But there is nevertheless a small chance that the magma cannot find an escape route and remains belowground for the foreseeable future.