Volcano near evacuated Iceland town finally erupts

After a month of relative quiet, what caused the latest Iceland eruption near Grindavík? Read the latest developments here.
 

By Melissa Scruggs, Ph.D. (@VolcanoDoc)
 

Citation: Scruggs, Melissa A., 2023, Volcano near evacuated Iceland town finally erupts, Temblor, http://doi.org/10.32858/temblor.332
 

Over a month ago, the sleepy fishing village of Grindavík was evacuated after thousands of earthquakes struck the Reykjanes Peninsula, signaling that magma was rising from below, only to stop just before it reached Earth’s surface. While scientists and emergency managers rushed to understand what was happening while also keeping residents safe, the world watched and waited for an eruption that seemed like it would never come. In fact, things appeared to be getting back to normal on the Reykjanes Peninsula after a month of uncertainty, but on December 19 at 10:17 p.m. local time (22:17 UTC), the magma body threatening to erupt finally breached the surface in a spectacular nighttime display at the Sundhnúka crater series.
 

 

We catch up on what government officials, scientists, first responders and residents have been doing to prepare for the Sundhnúka craters eruption, and what might happen now that lava is at the surface. For an in-depth look at how this all started, read this previous Temblor Earth News article on last month’s earthquake sequence.
 

 

Volcanoes are everyday life for Icelanders

Home to 32 active volcanoes, the island of Iceland is located in a unique geologic setting in which volcanic activity is so commonplace that heat it produces has been harnessed by Icelanders for more than 1,000 years. Geothermally generated electricity and heat account for more than 70% of the country’s energy consumption. Although most Icelandic eruptions are not explosive, the location of effusive eruptions (ones that do not produce sizable ash plumes) such as the ongoing Sundhnúka craters eruption can have significant implications, depending on what path the lava takes. In this case, the significant implications are for residents of the Reykjanes Peninsula.
 

 

 

Seismic lulls can give a false sense of security

On Nov. 10, 2023, a magma body as large as 30 Great Pyramids (about 70 million cubic meters) emplaced itself about a half-mile (less than 800 meters) beneath the village of Grindavík, extending over 9 miles (about 15 kilometers) to the north-northwest of the fishing village. Government officials and emergency responders evacuated the town in the middle of the night as magma pushed apart layers below the surface, rocking the Reykjanes Peninsula with thousands of earthquakes overnight.

Over the next week, thousands of earthquakes occurred daily as the ground readjusted to accommodate the volume of the newly emplaced magma body. First responders accompanied residents of Grindavík to their homes, where they were given only five minutes apiece to retrieve precious belongings and any pets inadvertently left behind. The threat of eruption within the town was so high that even this was considered dangerous. Grindavík residents were relocated to multiple refugee areas around the peninsula and construction began on large native stone barriers at strategic locations to protect the nearby Svartsengí Power Plant and other proximal infrastructure.

After the November 10 event, the ground northwest of Grindavík began to reinflate as magma was again supplied to a shallow region of magma storage located about 3 to 4 miles (roughly 5 to 6 kilometers) beneath the Svartsengí power plant. Although the near-surface intrusion continued to grow at a slower rate after November 10, GPS-based models suggested that magma supply to the shallow intrusion beneath Grindavík had stopped as of December 6. Even though the probability of an eruption had decreased, one could still happen if magma from the 3- to 4-mile-deep zone moved upward. Scientists expected that such an event would likely be preceded by large numbers of earthquakes — similar to the quakes generated by the previous month’s intrusion.

But, after weeks of no eruption and few earthquakes, it seemed possible that normal life could soon resume. Because the intensity and frequency of volcanic activity had continually decreased since the magma body had initially been emplaced, the public safety level was downgraded from emergency to danger on November 22. Residents were allowed to return home during daylight hours, but as time progressed, a few townsfolk felt the danger had passed and were found to have been staying in town overnight. And, as construction of the protective barriers surrounding Svartsengí continued, the Blue Lagoon partially reopened to tourists on December 17.
 

A volcanic eruption with little warning

The ground was quiet until about an hour and a half before the eruption, when a series of earthquakes occurred near Sundhnúka craters. Within 90 minutes, two fissures had opened, followed shortly by three more vents.
 

 

A magnitude 4.1 earthquake occurred a few minutes after the eruption began, but at least 400 earthquakes have been recorded over the duration of the eruption so far. As expected by scientists, volcanic activity weakened within a few hours, and now only three active vents remain. Lava continues to flow from the fissures as of this writing, and a State of Emergency has been declared for the area. The estimated volume of lava erupted thus far is 3.7 cubic kilometers, which is enough to cover Central Park in New York City and then some.
 

 

What caused the volcano to suddenly erupt?

If a magma body moves toward the surface but stalls before it can erupt, it will cool and crystallize in place to form an igneous rock. This is a fairly common process — most igneous intrusions do not result in volcanic eruptions. Between 1975 and 1984, nine eruptions took place within the Krafla caldera in northern Iceland — but there were also 15 intrusion events that did not end in an eruption. There are several reasons why a magma might not make it to the surface, two of which are that the magma might be too viscous to erupt (think of honey, which is more viscous than water; it doesn’t flow as easily), or it may be too dense to rise upward any farther. When an eruption happens, the driving pressure within Earth is enough to overcome these barriers, and the magma reaches the surface in a volcanic eruption.

It is simply too soon to know what happened to trigger this eruption. The (relatively) low numbers of earthquakes preceding the eruption suggest that a large volume of magma moving from about 3 to 4 miles (5 to 6 kilometers) deep toward the surface likely didn’t happen in the hour and a half before the eruption. However, deformation monitoring shows that the ground at Svartsengí has subsided 2 inches (5 centimeters) since the eruption began, suggesting that at least some magma was supplied from that region. Scientists have already begun to sample lavas and analyze their chemistry to better understand where this magma is coming from and its relationship to other recent eruptions on the Reykjanes Peninsula.
 

 

How does this eruption compare to previous peninsular exhalations?

The last three years have seen tourists from around the world flock to Iceland to see beautiful eruptions at nearby Fagradalsfjall. Scientists say that the power of the current eruption is comparable to those at Fagradalsfjall, and preliminary geochemical results suggest that the newly erupted Sundhnúka craters’ lavas are similar to the last-erupted lavas from Fagradalsfjall.
 

New whole-rock data! The 2023 Svartsengi magma has WR MgO 8.0 wt% and K2O/TiO2 0.23, nicely fitting the glass data. This magma is very similar to magmas erupted during the 2022 and 2023 Fagradasfjall eruptions, although slighly more fractionated. pic.twitter.com/k4yT8HwB2a

— Geochemistry and Petrology Group @ Uni. Iceland (@rockhardIES) December 20, 2023

 

Still, even though the Sundhnúka craters eruption is not a stereotypically explosive eruption, its location near a town and adjacent to critical infrastructure means that it could have much larger impacts on the rest of the country. It is unknown when Grindavík residents will be allowed to return home, or if the protective barriers surrounding Svartsengí will hold — or if they will even be needed at all. This all depends on the direction the lava flows, should they reach that far.
 

What might happen next?

The initial worst-case scenario on November 10 would have been an eruption within Grindavík’s town limits. Although that possibility still exists, the probability of it has decreased as fissures have opened uprift and remain just over a mile (2 kilometers) north of the village. Grindavik is built on top of lavas that erupted from Sundhnúkur craters around 342 BCE (2350 ± 90 before present; Jenness & Clifton, 2009), so the town could still be impacted by an eruption if either lava flows to the south or if new vents open and extend the eruption southward.

The majority of erupted lava is flowing to the east toward unpopulated areas, although a small volume flow is headed west, with the potential to reach populated areas. The Svartsengi Power Station doesn’t appear to be under threat at this time, but it and the adjacent Blue Lagoon have been evacuated for the safety of occupants. The roads into and out of Grindavik and the Blue Lagoon are closed, and people are encouraged to avoid the area as there remains a possibility that new vents could open in the ground with little to no warning.

Cities on the opposite side of the Peninsula could feel the effects of this eruption if wind patterns blow volcanic gases towards Reykjavik, and the Icelandic Meteorological Office has made an interactive map showing the gas pollution forecast available to the public. Protective barricades surrounding Svartsengí are nearly finished, ready to defend the Reykjanes Peninsula’s energy supply. Now we wait, watch and hope that the eruption will end as quickly as it began.
 

 

References

Blue Lagoon. (n.d.). Seismic activity at the Blue Lagoon. Retrieved December 19, 2023, from https://www.bluelagoon.com/seismic-activity

Iceland Civil Defense Facebook Page. 2023, December 19. https://www.facebook.com/Almannavarnir

Jenness, Maria H. & Clifton, Amy E. (2009) Controls on the geometry of a Holocene crater row: a field study from southwest Iceland. Bulletin of Volcanology, 71, p. 715-728. DOI: 10.1007/s00445-009-0267-9

Thorolfsson, G. (2005) Maintenance history of a geothermal plant: Svartsengi Iceland. Presented at the Proceedings of World Geothermal Congress, Antalya, Turkey, 24-29 April 2005. Retrieved December 19, 2023, from https://www.geothermal-energy.org/pdf/IGAstandard/WGC/2005/2037.pdf
 

For Further Reading

Much of the information provided in this article was reported by the Icelandic Meteorological Office. For further and official information on this eruption, please visit https://en.vedur.is/

Webcam(s) have been set up around the Grindavik area to observe the eruption:
https://www.youtube.com/watch?v=P1e_MWJ1nQc

If you would like to learn more about the history of geothermal energy use in Iceland, visit https://www.thinkgeoenergy.com/preparing-for-wgc-2020-a-short-history-of-geothermal-in-iceland/

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