How an unprecedented magma river surged beneath an Icelandic town

A river of magma flowed beneath an Icelandic fishing village late last year at a rate never before recorded, scientists said Thursday, as the region suffered a dramatic new eruption.

Icelandic authorities declared a state of emergency on Thursday as lava burst a key water pipe in the third volcanic fissure to hit the western Reykjanes peninsula since December.

Before 2021, the peninsula had not experienced an eruption in 800 years, suggesting that the region’s volcanic activity has awakened from its slumber.

After analyzing how magma gushed from a reservoir deep underground through a long, thin “vertical sheet” miles beneath the village of Grindavik in November, researchers warn that this activity shows no signs of slowing down.

This prediction appears to be borne out by the latest fissure that split the Earth’s surface near the now-evacuated village, occurring just hours before the new study was published in the journal Science.

The study’s lead author, Freysteinn Sigmundsson, a researcher at the Nordic Volcanology Center at the University of Iceland, told AFP it was difficult to say how long this new era of eruptions would last.

But he believes there are still months of uncertainty remaining for the threatened region.

A mighty molten river

Over six hours on November 10, rising magma created an underground dike 15 kilometers (nine miles) long and four kilometers (2.5 miles) high but only a few meters wide, according to the study.

Before Thursday’s eruption, 6.5 million cubic meters of magma had accumulated beneath the region surrounding Grindavik, according to the Icelandic Meteorological Office.

The magma flowed at a rate of 7,400 cubic meters per second, “a scale we’ve never measured before” in Iceland or elsewhere, Sigmundsson said.

For comparison, the average flow of the Seine in Paris is only 560 cubic meters per second. The magma flow was closer to that of large rivers like the Danube or the Yukon.

November’s magma flow was also 100 times higher than that observed before recent eruptions on the peninsula from 2021 to 2023, Sigmundsson said.

“Activity is accelerating,” he said.

November’s magma flow precipitated more serious eruptions in December, last month and Thursday.

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

Hidden crevasses that have riddled the city probably pose more danger than lava, Sigmundsson said, pointing to a discovery in the middle of a sports field earlier this week.

More magma to come

The village, as well as the nearby Svartsengi power station and the famous Blue Lagoon geothermal spa, have been repeatedly evacuated due to eruption threats.

The long-term viability of parts of the region located on such unstable terrain has become a subject of debate.

Sigmundsson stressed that such decisions were up to the authorities, but said it was clearly a “time of uncertainty for the city of Grindavik”.

“We need to prepare for a lot more magma to come to the surface,” he said.

The researchers used seismic measurements and satellite data to model the causes of magma flow.

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

As these plates slowly moved apart over the past eight centuries, “tectonic stress” developed, which was a key driving force for the rise of magma through the underground geological fissure, Sigmundsson said.

The researchers hope their analysis can inform efforts to understand the causes of eruptions in other parts of the world.

© 2024 AFP