For 800 Years, A River Of Lava Flowed Silently Beneath An Iceland Town

Scientists recently revealed that molten rock, known as magma, surged beneath an Icelandic fishing village at an unprecedented speed last year. This discovery coincides with the region's latest volcanic eruption, marking the third fissure to occur on the Reykjanes peninsula since December.

Icelandic authorities declared an emergency on Thursday after lava damaged a crucial water pipe, further complicating the situation. Before 2021, the peninsula hadn't witnessed an eruption for an astounding 800 years, suggesting a dramatic reawakening of volcanic activity.

Analyzing how magma travelled upward from a deep underground reservoir through a kilometres-long "vertical sheet" beneath the evacuated village of Grindavik in November, researchers warn that the activity shows no signs of ceasing. This prediction was tragically confirmed by the latest fissure splitting the Earth's surface near the village, happening just hours before the study's publication in Science.

Freysteinn Sigmundsson, lead author and researcher at the University of Iceland's Nordic Volcanological Centre, acknowledged the difficulty in predicting the duration of this newfound volcanic era. He warned of potential uncertainty persisting for several months in the affected region.

Imagine a giant underground crack, 15 kilometres long and 4 kilometres high, but incredibly thin - like a sheet of paper standing on its end. That's what a massive surge of magma created beneath the Icelandic village of Grindavik over six hours last November, according to a new study.

This "dyke," as scientists call it, formed after a whopping 6.5 million cubic meters of magma built up underground near Grindavik. And guess what? It wasn't the only volcanic surprise Iceland had in store - just days later, the region erupted!

This study highlights the dramatic activity happening beneath the Reykjanes peninsula, which hadn't seen an eruption in 800 years before 2021. So, while the dyke itself might be narrow, the volcanic potential seems much wider!

The magma had flowed at 7,400 cubic metres per second, "a scale we have not measured before" in Iceland or elsewhere, Sigmundsson said.

For comparison, the average flow of the Seine River in Paris is just 560 cubic metres a second. The magma flow was closer to those of larger rivers such as the Danube or Yukon.

The magma flow in November was also 100 times greater than those seen before the recent eruptions on the peninsula from 2021 to 2023, Sigmundsson said. 

"The activity is speeding up," he said.

The November magma flow precipitated more serious eruptions in December, last month and again on Thursday.

Increasing underground pressure has also led to hundreds of earthquakes and pushed the ground upwards a few millimetres every day, creating huge cracks in the ground and damaging infrastructure in and around Grindavik.

The hidden crevasses that have riddled the town likely pose more danger than lava, Sigmundsson said, pointing to one discovered in the middle of a sports pitch earlier this week.

The village, as well as the nearby Svartsengi power plant and the famed Blue Lagoon geothermal spa, have been repeatedly evacuated because of the eruption threats.

The long-term viability of parts of the region sitting on such volatile ground has become a matter of debate.

Sigmundsson emphasised that such decisions were up to the authorities, but said this was definitely "a period of uncertainty for the town of Grindavik".

"We need to be prepared for a lot more magma to come to the surface," he said.

The researchers used seismic measurements and satellite data to model what was driving the magma flow.

Iceland sits on the Mid-Atlantic Ridge, a crack in the ocean floor separating the Eurasian and North American tectonic plates.

As these plates have slowly moved apart over the last eight centuries, "tectonic stress" built up that was a key driving force for magma to surge through the underground geological crack, Sigmundsson said.

The researchers hope their analysis could inform efforts to understand what causes eruptions in other areas of the world.