The Reykjanes peninsula in southwest Iceland trembled with an intense swarm of earthquakes on the afternoon of 10 November. A whole lot of quakes had been detected on the regional networks of seismometers and several other had been robust sufficient to be felt in Reykjavik, 50km away.
A civil safety alert was referred to as warning of the danger of an eruption – which might be the fourth since 2021.
Why is that this occurring once more, and what would possibly occur subsequent?
The geology of volcanoes
Iceland straddles the Mid-Atlantic Ridge the place the North American and Eurasian plates creep aside at about 2cm a yr. Within the Earth’s mantle under floor, the place rocks behave like very stiff toffee, the plates can prolong constantly.
However close to the floor the rocks of Earth’s crust are chilly and brittle, and so they can solely stretch by breaking. Like pulling the ends of a chocolate bar with a comfortable inside however a tough shell, the build-up of pressure because the plates pull aside is launched in bursts because the coating breaks.
A lava area shaped after the 2021 eruption of the Fagradalsfjall volcano. The location is positioned a number of kilometres from Grindavik, Iceland, which is making ready for one more volcanic eruption. Supply: AAP / Raul Moreno / SOPA Pictures / Sipa USA
The Reykjanes peninsula varieties the southwestern tip of Iceland, the place the mid-Atlantic rift rises out of the ocean. Right here, the crust responds to inexorable tectonic forces by breaking each few hundred years, forming a rift.
The final sequence of rifting and eruptions right here was over 800 years in the past. Since then, the plates ought to have moved aside by about 16 metres.
We at the moment are in one other part of rifting marked by lots of to 1000’s of earthquakes, many massive sufficient to be felt throughout southwestern Iceland and all pushed by the arrival of magma close to the floor.
Every earthquake and eruption releases a bit extra pent-up movement in these tectonic plates, and finally, when that pressure has been launched, the eruptions will cease. We now have seen comparable bursts of rifting and eruption a few occasions previously 50 years all over the world.
From 1975 to 1984, 18 earthquake swarms and 9 lava eruptions struck northern Iceland throughout the Krafla fires. Between 2005 and 2010, 14 earthquake swarms and three eruptions occurred alongside an 80km part of a rift valley in Afar, northern Ethiopia.
As in any respect oceanic ridges, the rifting course of is lubricated by magma. Magma is forming constantly at depth, and its buoyancy signifies that it’s destined to rise.
Within the brittle crust, the magma can solely rise as soon as there are some fractures to comply with. However as soon as it begins to rise, it can power its strategy to shallower and shallower depths, growing the danger of eruptions.
The view from above
The scientists of the Icelandic Meteorological Workplace can detect what is occurring at depth and find the tiniest of shakes utilizing networks of seismometers. These alert the crew to the contemporary breaking of rock within the crust and pinpoint the place it’s occurring.
Sensors speaking with constellations of navigation satellites can present spot measurements of the tiny actions of the Earth’s floor and radar satellite tv for pc photos can be utilized to map out and measure the three-dimensional form of the altering floor.
The earthquake swarm that started in late October is the newest in a sequence of occasions that began in early 2020, and which has thus far culminated in three eruptions on the Fagradalsfjall volcanic system in southwest Iceland in 2021, 2022 and most lately, summer season 2023.
There may be growing concern a few potential volcanic eruption close to Grindavik, southwestern Iceland, which has led civil protection authorities to declare a state of emergency within the area. Supply: AAP / Brynjar Gunnarsson / AP
When the earthquakes started this time, they clustered round and beneath one other volcanic system – Thorbjörn, 10 kilometres west of Fagradalsfjall. To begin with, there was no seen deformation of the Earth’s floor and it wasn’t clear whether or not this was only a little bit of the crust readjusting to the earlier episode of rifting.
However as soon as the indicators confirmed that the Earth’s floor was beginning to bulge, this indicated new magma was coming into the crust. Over the previous weekend, issues developed quickly. The scale, quantity and places of earthquakes all pointed to the filling of a fracture within the crust with magma at about 5km depth.
Because the magma continued to movement into it, the guidelines of the fracture opened up, breaking a path via the crust till the brand new dike was about 15km lengthy. The magma hasn’t but reached the floor, however the patterns of floor motion and pc fashions counsel {that a} pool of magma has now collected inside a kilometre of the floor.
Is an eruption imminent?
On the time of writing, it appears fairly seemingly that this magma will break via to the floor and begin an eruption. However the monitoring groups will solely know when and the place that is about to occur as soon as they spot the tell-tale indicators of transferring magma.
These indicators may embrace the repetitive “hum” of a volcanic tremor, signalling that magma might erupt inside hours, or earthquakes proliferating at very shallow depths.
For now, the dike seems to increase straight beneath the city of Grindavik, a fishing neighborhood close to Iceland’s southwestern tip.
If there may be an eruption onto the land floor, it’s prone to be much like the eruptions of 2021–2023 at Fagradalsfjall, with a crack or fissure opening on the Earth’s floor and fountains of purple scorching molten rock, with lava flowing downhill and away from the eruption web site.
This may pose a risk relying on the place the eruption begins and the way far the lava flows. Fuel fumes launched from erupting magma mixed with the burning of peat and vegetation may create poisonous air relying on eruption charges and wind instructions.
If an eruption begins throughout the city of Grindavik, the results may very well be much like these of the eruption of Eldfell which buried part of the city of Heimaey in 1973. Therefore the pre-emptive evacuation of the city, of the close by Svartsengi geothermal energy station and the Blue Lagoon, considered one of Iceland’s best-known vacationer sights.
If an eruption begins on the southern finish of the dike which extends offshore, scorching lava assembly seawater in a submarine eruption may generate small-scale explosions and native ash clouds, and launch additional noxious gases from the boiling sea water.
Whereas this in all probability wouldn’t have results as widespread as these of the 2010 Eyjafjallajökull eruption, which closed the air house over a large space of northern Europe for a number of weeks, even a small submarine eruption would add to the challenges that the authorities should handle even in a well-prepared nation like Iceland.
