Over the past few years, we've seen multiple volcanic eruptions on the Reykjanes Peninsula in Iceland at Fagradalsfjall. These eruptions have been a tourist boon, with lava fountains and lava flows pouring out over a mostly barren landscape not far from the nation's capital city. A third eruption might be starting soon, but the playing field is suddenly much different. The focus of earthquakes, cracks in the landscape and inflation is underneath the town of Grindavík, a fishing village with a population of nearly 4,000 people.
Grindavík is likely most famous for the Blue Lagoon (Bláa lónið), a hydrothermal area where locals and tourists go to soak in the waters warmed by the hot rocks of the Reykjanes Peninsula. The heat from the subsurface also powers the Svartsengi geothermal power station, one of the many such plants across Iceland. The harbor at Grindavík has made it ideal for fishing as far back as 1,000 years.
Earthquakes Shake Grindavík
Over the past month, the area has been experiencing frequent earthquakes, some of them topping out near M5. The earthquakes have delineated a roughly NE-SW line that runs from the Atlantic Ocean to the south, across Grindavík and into the interior of the Reykjanes Peninsula.
The Icelandic Meteorological Office (IMO) has said that these earthquakes are very likely being caused by a magmatic dike intruding under the area. This means that a body of molten rock is rising up, likely along a weakness in the crust, forming this straight line of earthquakes as it goes. Over 800 earthquakes have occurred in the past 24 hours alone, leading to a declaration of a state of emergency by the Icelandic government.
On top of this shaking of the land, in the past few days large cracks have started to form in and around Grindavík. There are some spectacular images of cracks tens of meters wide opening in the golf course near the Blue Lagoon spa. These cracks may be forming due to the stress from the earthquakes or from the deformation of the land from magma rising up under the area.
Where is the Magma?
The IMO has placed the dike just to the northwest of Grindavík, between the town and the Blue Lagoon. As of November 11, the IMO has issued a warning that an eruption is very likely to occur somewhere along the line. The most intense deformation does appear to be happening just to the south of Mt. Porbjörn, so that could be the spot that is most likely to see an eruption. Since November 4, it appears that the magma has risen 3-4 kilometers.
The style of eruptions on the Reykjanes Peninsula share characteristics with eruptions of the same type of basaltic lava in Hawai'i. This pattern of earthquakes and fissures (note: the cracks forming now are not necessarily these fissures ... they might be associated with the earthquakes) are very common in the days to hours before an eruption starts in both areas. Right before an eruption begins, we might also expect to see dense volcanic gas emissions from these fissures as the magma gets closer to the surface.
The most recent IMO statement places the magma less than a kilometer beneath the surface. However, the rate at which it is rising is unclear, so forecasting when an eruption might start is challenging. That being said, all precautions are being taken by Icelandic authorities. Grindavík is being evacuated and the IMO has also warned that there is the potential for some explosive activity if the eruption starts just offshore under the sea.
The location of this intrusion may remind some people of the eruptions at Heimaey that started in January 1973. This eruption had much the same signs and nearly destroyed the fishing harbor of that town. Heimaey was one of the few examples where human interaction may have prevented the lava flows from wrecking the opening of the harbor. Local authorities used seawater to cool the lava as the flows approached, helping stop their movement. However, significant damage was done to the town itself, but luckily it has recovered. Today, the cone from that eruption (Eldfell) looms over the town.
Past Icelandic Eruptions
If the eruption begins underwater, then we might see something like the November 1963 Surtsey eruption off the coast of Iceland. During that eruption, a new island was born as a submarine eruption that started explosively thanks to the mixing of lava and seawater ended as lava flows that built the small landmass. This eruption even gave its name to the style of shallow, submarine basaltic eruptions: Surtseyan.
One of the big questions beyond when the eruption might start near Grindavík is just how big it will be. The estimates from the IMO on the rates of magma filling in under the area are around 7 cubic meters per second, which is multiple times larger than the previous eruptions over the past few years on the Peninsula. This could be that the eruption may be larger than what we've see so far.
Right now, it is a waiting game. There are a number of livestreams right now looking out over the Grindavík area, so if any eruption happens, you might be able to catch it live. However, exactly when and where this eruption might start is still unknown. We can just hope that it doesn't cause much damage to the lives and homes of the people in Grindavík.