17 Feb 2024

Iceland volcano: How earthquakes signal mammoth magma flows

8:57 pm on 17 February 2024
Lava flows in Iceland after the latest eruption in Grindavík on February 8, 2024.

Lava flows in Iceland after the latest eruption in Grindavík on February 8, 2024. Photo: Gregory De Pascale

In November 2023, a magma dike began to rapidly build below the Sundhnúkur crater chain in southwest Iceland.

It caused widespread damage and forced the local population of Grindavík to pack up their belongings and quickly leave their homes. Since then, the volcanic chain has erupted three times, most recently on 8 February, sending lava spilling across the Reykjanes Peninsula.

New research has revealed Grindavík's 15-kilometre-long magma dike formed in record time, peaking at an unprecedented flow rate of 7400 cubic metres per second.

The authors of the study say it demonstrates serious potential for further volcanic eruptions.

Dr Gregory De Pascale who is an associate professor of geology at the University of Iceland said that several earthquakes first signalled something was happening deep below the ground.

"There was a sequence of earthquakes and essentially the plate boundaries and extensional plate boundaries.

"So, the plates are being ripped apart, and during these earthquakes there are a number of faults that moved and accommodated that deformation. And so, a rift valley was forming right underneath and within this town of Grindavik."

De Pascale said these events saw an injection of magma that was flowing at an incredibly fast rate and in high volume through rocks resulting in incredible stresses.

To put this into context, the highest flow rate river in New Zealand, the Clutha, is about 600 metres per second.

Add all the flow rates in terms of metres cubed per second of the top 10 rivers in New Zealand and it was still less than the flow rate of 7400 underneath the town of Grindavik, De Pascale said.

"It's pretty astonishing just to try to get your head around how big and how fast that is."

This area of Iceland last saw major geological activity 800 years ago lasting 200 years - early Icelandic settlers would have witnessed volcanic cones forming.

Prior to this, most eruptions have happened in the middle of nowhere.

De Pascale said these were called "tourist events"- people would show up and watch rocks being formed from lava flows.

Molten lava is seen overflowing the road leading to the famous tourist destination "Blue Lagoon" near Grindavik, western Iceland on February 8, 2023. A volcanic eruption started on the Reykjanes peninsula in southwestern Iceland on Thursday, the third to hit the area since December, authorities said. (Photo by Kristinn Magnusson / AFP)

Photo: Kristinn Magnusson / AFP

However, the event in Grindavik was different. It's no longer a tourist event and the town has since been abandoned following the initial quakes which caused damage to key infrastructure.

"Homes, businesses, the economy is being affected and, in some ways it's a similar situation to what happened in Christchurch during the Canterbury earthquakes.

"The whole discussion about red zoning homes, these same discussions have been taking place in Iceland because it's fairly clear to the experts that a lot of these homes that are located along fault lines have been damaged irreparably."

The damage was felt on a national scale as geothermal pipes that supply energy and heating to Icelandic homes were hit by the lava flows.

Iceland's Svartsengi power station.

Authorities said on 14 November, 2023, that they were preparing to build defence walls around Iceland's Svartsengi geothermal power station to try to protect it from lava flows amid concerns about an imminent volcanic eruption. Photo: Philippe Turpin / Photononstop / Photononstop via AFP

"Most of the homes in Iceland are heated through regional hot water supply. So basically these large diameter pipes pump hot water and the hot water heat up radiators in people's homes and this lava flow took it out.

"One of these pipes that actually heats about 30,000 people's homes and it was -10C that day when this happened. So the consequences were very extreme. It also stressed out the electric system."

Inflation and deflation

The study has looked at the magma rivers flowing deep below the Earth in other regions of the world in order to get a better understanding of detecting geological inflation and deflation of the sub-surface.

"Essentially, this inflation takes place, and we can observe it from satellites. So, basically the ground starts getting closer to the satellites.

"So, the distance between the satellite and the ground is lessened, and we know that the ground is inflating."

These warning signs could help countries to build more resilient infrastructure and prepare better for possible earthquakes and magma flows. The swarm of earthquakes in Iceland allowed authorities to save lives and evacuate Grindavik in advance of the magma eruption.

This photo, taken on 13 November, 2023, shows a member of the emergency services walking near a crack cutting across the main road in Grindavik, southwestern Iceland following earthquakes. The town - home to around 4,000 people - was evacuated in the early hours of 11 November after magma shifting under the Earth's crust caused hundreds of earthquakes in what experts warned could be a precursor to a volcanic eruption.

A member of the emergency services walks near a crack cutting across the main road in Grindavik, southwestern Iceland. The town - home to around 4,000 people - was evacuated in the early hours of 11 November. Photo: KJARTAN TORBJOERNSSON / AFP

De Pascale said that while this was exciting work it could also be terrifying when you saw the impact on infrastructure and communities.

"It kind of reminds me of places like the Hikurangi subduction zone, which is just to the east of the North Island, it seems to sit quiet for a couple of hundred to 400 years.

"And then there is one of these huge earthquakes.

"That probably generates a huge tsunami and has a whole bunch of detrimental effects around the eastern side of New Zealand, so it just shows that over geologic time sometimes it takes time for these systems to build up stress, but once they start going the consequences are huge."

De Pascale points out that Iceland has been relatively lucky.

"It's not as severe as the Taupō volcano blowing up or one of the super volcanoes we have on this planet, blowing its head, that could have a huge consequence on agriculture and everything else."

While the events are exciting from a scientific point of view, De Pascale concedes he is mindful of the impact they have on those living in these unstable places.

"Seeing lava rushing across burning a road and then hitting the hot water pipes and seeing the hot water pipes explode and shoot all the steam into the air, I mean, you start feeling the consequence of that."