How Fagradalsfjall Volcano Compares to Mt. St. Helens as Iceland Eruption Looms

Iceland's Fagradalsfjall volcano could be just moments away from its next eruption following an uptick in activity about a month ago.

The country is in a state of emergency, and thousands of people have been evacuated from the nearby town of Grindavík.

Iceland is no stranger to volcanic activity, being one of the most geologically active countries on the globe. The country lies on Mid Atlantic Ridge, a region where the Eurasian and North American tectonic plates continuously shift, moving several inches apart per year. It also lies above a suspected hot spot, where the land is fed by hot rock in the Earth's mantle.

Eruptions have occurred along the Reykjanes Peninsula in recent years, but Fagradalsfjall is situated in more populated areas, meaning it is of particular concern.

Fagradalsfjall is not the only volcano rumbling to life. Washington state's Mount St. Helens, which is one of the most dangerous volcanoes in the U.S., has seen an uptick in earthquakes since mid-July. This is the most active the volcano has been since it last erupted.

So, how do these two rumbling volcanoes compare?

"They are very different systems—St. Helens' magmas are very much more viscous, and richer in silica than the Icelandic magmas," David Pyle, a volcanologist and professor of earth sciences at the University of Oxford, told Newsweek. "The Iceland magmas are basalts—rich in MgO [magnesium oxide] and relatively poor in silica—and these have arrived in the shallow crust fairly quickly, and without changing much from when they formed. They are much more likely to erupt to form fluid lava flows, while St. Helens' magmas either form very slow-moving domes of lava, or erupt explosively."

Volcanoes with silica-rich magmas like this produce what is known as a "stratovolcano" —a cone shaped mountain with steep sides. Runny basaltic magmas tend to produce lower-lying shield volcanoes.

Fagradalsfjall could be more closely compared to Hawaii's Kilauea, which is one of the most active volcanoes in the world. Kilauea has also been displaying an uptick in activity recently, though this is not unusual.

"The Icelandic magmas are broadly similar to the lavas that erupt at Kilauea—they will erupt at high temperature, and probably start erupting along fissures or fractures in the crust, and then flow away as lavas," Pyle said.

Kilauea's eruptions usually stay confined in the crater, meaning it does not usually pose a danger to surrounding communities. However, it is still considered dangerous. In 2018, a Kilauea eruption caused large lava flows throughout the Puna District, which destroyed more than 700 homes from May through August.

Despite there being similar features between Fagradalsfjall and Kilauea, every volcano is different. And even though scientists have a good idea as to what may predate an eruption, they are still difficult to predict.

Fagradalsfjall has been displaying some worrying signs since a month ago. In recent days, expert have been watching the volcano closely—and it is unlikely that those who have evacuated will return any time soon.

"The last 3 eruptions in 2021-2023 were indeed at Fagradalsfjall, but the current activity is now focused under a different section of the Icelandic rift system, called Svartsengi," Pyle said. "At Svartsengi, we have seen a 'dike' of magma form: a pulse of molten magma pushed up through the Earth's crust and then fed into a fracture that is about 15 km long and between 3 and 5 km below the surface. This was the cause of the very strong earthquake swarm that stretched under Grindavík about ten days ago."

Since then, the volcano's magma has continued to collect and some has risen close to the surface.

"The scientists on Iceland can tell this, from the way that the Earth's surface is continuing to bulge in places. At the moment, the bulging is continuing, but a bit more slowly; and the numbers of earthquakes has fallen. It is likely that the magma is starting to freeze against the edges of the dike in places, but there is still a lot of molten rock below the surface," Pyle said.

Experts believe that an eruption would be similar to the last three that occurred. Other than evacuations, Icelandic volcanoes have caused other kinds of chaos in previous eruptions.

Eyjafjallajökull, which is located to the southwest of the island, caused the cancellation of 95,000 flights in 2010 following an eruption. It was one of the largest air-traffic shutdowns ever seen. The flight cancellations followed concerns over the huge amount of ash that plumed into the atmosphere. The glacier on top of the volcano caused the lava to cool rapidly—this created ice particles that flew into the air by steam. This spread all over the skies in Europe, posing a serious hazard to aircraft. Volcanic ash can wear down propellers and jet engine blades, as well as impair a pilot's visibility.

That incident was extremely rare. While volcanic eruptions can occasionally cause flight disruption, chaos on such a scale is not expected due to Fagradalsfjall.

"But it remains unclear when, or if, an eruption will happen. The chance of an eruption is still thought to be quite high; but we also know that pulses of magma often push into the crust, and fill fractures inside the crust to form dikes without erupting," Pyle said.

"For now, the best that we can do is to keep a close watch on the signals—earthquakes, deformation, and on any volcanic gases that might be leaking out of the surface fractures—to keep one step ahead."