On 11 November 2023 residents of the town of Grindavík on the Reykjanes Peninsula, Iceland, were evacuated from their homes following a major increase in seismic activity beneath the nearby Fagradalsfjall Volcano. The evacuations were triggered by the discovery of a magma tunnel running directly beneath the town at a depth of about 1.5 km. This is about 12 km long, originating near Stóra-Skógfell hill, and running beneath the town and some way out to sea. Seismic activity in the area has remained high in the area in the intervening weeks, although some people had begun to return to their homes.
Slightly after 10.15 pm on Monday 18 December 2023, a new volcanic fissure opened on the peninsula, spewing vast amounts of lava and prompting a new series of evacuations. The fissure is about 3.5 km in length, and about 3 km from the town of Grindavík. It is currently producing 100-200 m³ of lava per second, although this is not flowing towards the town, and is not thought to present a threat to Human life.
Although dramatic, lava flows are not usually considered particularly dangerous, as their advancing fronts are quite slow and can quickly be outpaced by an able-bodied Human being. The more deadly volcanic events are pyroclastic flows, such as the one which engulphed the Roman town of Pompeii, in which clouds of superheated gas and ash move downhill at high speeds in an avalanche-like motion, and phreatic explosions, caused by bodies of lava encountering bodies of water, which evaporate almost instantly, causing huge explosions.
Iceland lies directly upon the Mid-Atlantic Ridge, a chain of (mostly) submerged volcanoes running the length of the Atlantic Ocean along which the ocean is splitting apart, with new material forming at the fringes of the North American and European Plates beneath the sea (or, in Iceland, above it). The Atlantic is spreading at an average rate of 25 mm per year, with new seafloor being produced along the rift volcanically, i.e. by basaltic magma erupting from below. The ridge itself takes the form of a chain of volcanic mountains running the length of the ocean, fed by the upwelling of magma beneath the diverging plates. In places this produces volcanic activity above the waves, in the Azores, on Iceland and on Jan Mayen Island. All of this results in considerable Earth-movement beneath Iceland, where Earthquakes are a frequent event.
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