“Some think the systems are deeply intertwined,” says Edward Marshall, a geochemist at the University of Iceland, either directly, with the magma circulating between the two underground labyrinths, or indirectly, where they exchange pressure. But any geological connection between Fagradalsfjall and Svartsengi is tenuous to say the least, making it difficult to understand why magma rises several times at the former and then shifts to the latter.
This investigative effort is further complicated by the additional particularities of the current crisis. In recent years, Thorbjörn, a volcanic mound near the Svartsengi geothermal power station and Grindavík, has occasionally bulged, perhaps due to the movement of magma somewhere below, but it has always ended without incident. The events of last week “certainly mark a break in this trend,” says Tom Windervolcanic seismologist at the University of Cambridge.
Early estimates suggest that the amount of magma involved is greater than in the last three eruptions on the peninsula, and that it also flowed into the Svartsengi region at an astonishing speed. “Why the magma influx rate seems so much higher this time, and where it came from, remains an important open question,” says Winder. Given the apparently large volume of magma, the potential for a long-lasting eruption, or an otherwise very prolific lava eruption, is high – but paradoxically, as with many eruptions, it may be that only a fraction of this molten rock sees the light of day. .
The fact that the magma rushed toward Grindavík late last week, then stopped just beneath its now-empty streets, engendered both curiosity and anxiety. The reasons for this interlude are not very clear. In the 2021 eruption, there was a three-week interval between the magma curtain invading the shallow basement and the emergence of the eruption itself. The same thing could happen this time. Or, it may flare up after you finish reading this article – there is no surefire way to know.
It’s not even certain that there will be an eruption. Currently, given the proximity of the magma to the surface and the constant seismic rumble, the Icelandic Meteorological Office suspects that there is a very high probability of an eruption, somewhere along this 16 km long line of deformed and shaking ground, in the coming days. But there is nevertheless a small chance that the magma will not find an escape route and will remain underground for the foreseeable future.