Update, 21 December 2023: IMO reported that lava has stopped flowing from the fissure. It may still be moving within closed channels, so it is too soon to declare the eruption over.
At 10:17 p.m. local time on 18 December, a magma fissure erupted on Iceland’s Reykjanes Peninsula between Sýlingarfell and Hagafell. An earthquake swarm north of Grindavík preceded the eruption by an hour. Scientists at the Icelandic Meteorological Office (IMO) and local emergency managers were monitoring the area closely after months of seismic unrest and other eruption precursors.
The eruptive fissure is 4 kilometers long, and its southern tip is about 3 kilometers north of Grindavík, which was fully evacuated several weeks ago. IMO estimated that the rate of lava discharge was hundreds of cubic meters per second during the first 2 hours.
The Icelandic Coast Guard captured this video of the initial eruption from a helicopter:
Since the eruption began, the flow rate has slowed by 75%, the length of the actively erupting fissure has shortened by about two thirds, and seismic activity has decreased. “It is often the case with these eruptions that they are the most powerful at the beginning,” Kristín Jónsdóttir of IMO told RÚV, Iceland’s national news outlet.
This is the fourth eruption of the Fagradalsfjall volcano complex in 3 years and is 3–4 times larger than previous ones, according to volcanologist Ármann Höskuldsson at the University of Iceland. The agency cannot predict how long this eruption might last, “but given how powerful this is and how long this crack is, it is likely that it will last longer than 3 weeks,” Jónsdóttir said.
Iceland’s national police commissioner declared a Civil Defense emergency level. Local police chief Úlfar Lúðvíksson said that no one should be in immediate danger, RÚV reported, despite reports that some Grindavík residents might have returned to the town ahead of the holidays. Civil Defense contractors who had been building defensive walls are also safe, and the nearby Blue Lagoon geothermal spa, which reopened at the beginning of the month, is closed again and was empty at the time of eruption.
As of 19 December, the fissure opening had spread northward, and lava was flowing away from Grindavík. Winds have been “favorable,” RÚV reports, though according to IMO, gas pollution might be noticeable later today in the Vestmannaeyjar archipelago (population 4,400) and as far away as the capital, Reykjavík.
You can watch the eruption live here:
—Kimberly M. S. Cartier (@AstroKimCartier), Staff Writer