Iceland volcano: Mass of magma pooling beneath ground north of Grindavík indicates imminent eruption

UPDATE: The volcano in Iceland erupted for the third time at around 6:00 a.m. local time on Thursday (Feb. 8). 

The risk of a volcanic eruption on Iceland's Reykjanes Peninsula is once again growing as magma continues to pool in the area 2.5 miles (4 kilometers) north of the fishing town of Grindavík, according to the Icelandic Met Office (IMO).

An estimated 318 million cubic feet (9 million cubic meters) of magma now sits beneath Svartsengi, which is home to the Blue Lagoon resort and Svartsengi geothermal power plant. That's equivalent to the volume of around 3,600 Olympic-sized swimming pools. 

Five days ago, on Feb. 1, the volume of magma was reported to be 230 million cubic feet (6.5 million cubic m), with the IMO already warning officials that the volcano was primed to erupt again. "The estimated amount of magma under Svartsengi has now reached the lower limit of the amount believed to have accumulated there before the last eruption," IMO representatives wrote in a translated statement on Monday (Feb. 5).

Between 318 million and 460 million cubic feet (9 million and 13 million cubic m) of magma are thought to have accumulated in the same chamber before an eruption on Jan. 14 that sent lava coursing toward Grindavík.

Related: Iceland villages in danger of 'crack collapse,' ground swelling following volcanic eruption

The land began rising again following the eruption and continues to inflate as molten rock gathers under the surface, although the rate has slowed in the last few days, according to the IMO statement. This pattern is the same as land movements recorded in the weeks and days preceding the eruption on Jan. 14 and a previous eruption in December 2023.

"There is therefore an increased probability of magma flow and eruption in the coming days or weeks," IMO representatives wrote.

Predicting when and where an eruption will take place is not possible. A hazard map released by the IMO shows the areas believed to be at greatest risk, with a corridor stretching from Grindavík in the south to Stóra-skógafell to the northeast. Svartsengi, where the magma is pooling, is considered at a very low risk of a volcanic eruption.

However, temperature and pressure measurements taken from boreholes in Svartsengi could provide a warning that another eruption is on its way.

"We saw a substantial increase in the pressure in the boreholes before the dyke intrusion on Nov. 10," Lilja Magnúsdóttir, the director of resource management at HS Orka geothermal power plant in Svartsengi, told Live Science in an email. A similar increase in pressure was also recorded ahead of the eruption on Dec. 18, alerting staff to the possibility that another dike intrusion could culminate in an eruption. 

"Around 40 [to] 50 minutes later, it erupted," Magnúsdóttir said. "So we made an automatic program to detect this signal. If an alert is triggered, the program sends a warning email to our shift at HS Orka and to the Icelandic Meteorological Office."

The program issued a warning in the early hours of Jan. 14, foreshadowing an eruption four hours and 20 minutes later, Magnúsdóttir said. "We were also able to predict that it would erupt further south than in the previous eruption," thanks to a stark change in pressure on the southern boundary of the geothermal reservoir, she added.

Editor's note: This article has been corrected to say Svartsengi is not at risk of a volcanic eruption. It has been updated to include the current hazard map and to remove a quote from Magnúsdóttir.