At 20.45 (8,45 p.m.) on Friday evening March 19th. 2021 an eruption started in a mountain area north east of the town Grindavik. This area is close to the mountain Fagradalsfjall and the valley´s name is Geldingadalur. When it comes to eruptions, geologists know that nothing is certain, but a few weeks before the eruption, thousands of earthquakes, up to 5,2 on the Richter scale occurred. The lava from this eruption comes from a depth 17-20 km, which is unusually deep and it might be of the sort called Dyngjugos or Shield volcano. These eruptions can last for many months, years or even decades.
Reykjanes peninsula is the youngest area of Iceland and hosts 5 active volcanic systems. The names of these volcanic systems are: The Reykjanes system which is farthest to the west, The Svartsengi system north of Grindavík and where the geothermal power plant and the Blue lagoon are. The Fagradalsfjall system where the eruption is now in Geldingadalir. The Krýsuvík system where the hot springs in Seltun are. The last one is the Brennisteinsfjöll system farthest east and reaches the Bláfjöll mountain area.
The last eruptions in Reykjanes peninsula happened about 780 years ago in 1211-1240 in the Reykjanes volcanic system. The last eruption in the Fagradalsfjall system happened over 6000 years ago so as always nature is quite unpredictable.
Now we wait to see if this eruption will fade out in a few days or weeks or if it will last for decades which we have many examples of with shield volcanoes.