A fissure eruption in the area between Sundhnúkur and Stóra Skógfell on the Reykjanes peninsula began at 0602 on 8 February after around 30 minutes of intense seismic activity, prompting IMO to raise the Aviation Color Code to Red (the highest level on a four-color scale). During a helicopter overflight the location of the fissure was confirmed to be near the 18 December 2023 fissure, less than 1 km NE of Sylingarfell. The fissure lengthened to 3 km N-S, with lava flows moving W and E. Lava fountains along the fissure rose 50-80 m high and a volcanic plume mainly comprised of gas and steam rose to 3 km. IMO lowered the Aviation Color Code to Orange at 0626, noting that ash was not present in the plume. Tephra fall was reported in parts of Grindavík, 3-5 km S of the fissure. Visitors to the Blue Lagoon were evacuated; there were no residents in Grindavík due to previous evacuations.

Deformation in the dike area had significantly decreased by noon, and the intensity of the eruption had also declined, with only three active craters along the fissure. Emissions from the fissure drifted SW. Lava advanced N, curving around the Stóra Skógfell cones and branching to the SW. The SW branch advanced at a rate of about 500 m per hour, according to a news article, and flowed over both Grindavíkurvegur (Road 43) and Bláalóns-road, at the exit for the Blue Lagoon, at around noon. Lava also advanced over the pipeline that supplied hot water to Svartsengi. Power lines were also affected by the flows, though electricity was restored later that day.

Minor explosive activity generated from the interaction of magma and ground water began during 1300-1400 on 8 February and produced dark plumes rising as high as 2.5 km from the middle of the fissure and drifting S. The explosive activity was mainly over by 1715 and the intensity of the eruption continued to decrease. Deformation was no longer being detected, suggesting that magma was no longer ascending at the same pressure as at the beginning of the eruption. Seismic activity significantly decreased after the onset of the eruption and remained at low levels with only about 20 small earthquakes recorded during 0800-1715. Lava flowed as far as 4.5 km W of the fissure. Activity and tremor levels fluctuated at low levels during the evening of the 8th and further decreased during 0700-0800 on 9 February, with only two craters active. No fountains were visible mid-morning; a drone overflight at around noon confirmed that activity had ceased. IMO lowered the Aviation Color Code to Yellow at 1713.

Deformation data suggested that inflation began again after the eruption had ended; model calculations showed that during 9-14 February an estimated two million cubic meters of magma had accumulated beneath the Svartsengi area, or about 20% of the volume of magma that had accumulated before the 8 February eruption. The hot water pipeline was restored by 12 February and the Blue Lagoon reopened to visitors on 16 February.

Geological Summary. The Reykjanes volcanic system at the SW tip of the Reykjanes Peninsula, where the Mid-Atlantic Ridge rises above sea level, comprises a broad area of postglacial basaltic crater rows and small shield volcanoes. The submarine Reykjaneshryggur volcanic system is contiguous with and is considered part of the Reykjanes volcanic system, which is the westernmost of a series of four closely-spaced en-echelon fissure systems that extend diagonally across the Reykjanes Peninsula. Most of the subaerial part of the system (also known as the Reykjanes/Svartsengi volcanic system) is covered by Holocene lavas. Subaerial eruptions have occurred in historical time during the 13th century at several locations on the NE-SW-trending fissure system, and numerous submarine eruptions dating back to the 12th century have been observed during historical time, some of which have formed ephemeral islands. Basaltic rocks of probable Holocene age have been recovered during dredging operations, and tephra deposits from earlier Holocene eruptions are preserved on the nearby Reykjanes Peninsula.

Sources: Icelandic Meteorological Office (IMO), Icelandic National Broadcasting Service (RUV), Icelandic National Broadcasting Service (RUV)