The Icelandic Meteorological Office has reported an eruption on Mount Fagradalsfjall, part of the Krýsuvík-Trölladyngja Volcanic System, on the Reykjanes Peninsula. The eruption started at about 8.45 pm local time on Friday 19 March 2021, with a fissure 500-700 m in length opening up to the southeast of the main volcano, and produced lava fountains up to about 100 m high, with the lava spreading to cover an area of about 1 km² by the next day. The eruption persisted for several days, but decreased in intensity steadily. While spectacular, the eruption was not particularly dangerous, attracting large crowds of onlookers, some of whom took the opportunity to cook sausages on the cooling lava.
The Krýsuvík-Trölladyngja Volcanic System comprises a composite fissure swarm about 50 km in length, with no central volcano, but several small shields (i.e. volcanic structures made up largely of overlapping lava deposits that resemble upturned bowls rather than a cone) including Mount Fagradalsfjall. The system has been essentially quiet for about 800 years, with the last known eruption happening in the fourteenth century, and the last major eruption two centuries before that. However, an eruption in the area was expected, as a very large number (over 50 000) of earthquakes had been recorded beneath the system over the past few weeks, something which is often indicative of fresh magma moving into chambers beneath inactive volcanoes.
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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