IMO reported that the fissure eruption that began at 1246 on 29 May near Sundhnúk, NE of Sýlingarfell, within the Reykanes volcanic system, continued to effuse lava during 30 May-4 June. The fissure consisted of several segments and had a total length of 3.4 km. Just before 1600 explosive activity occurred near Hagafell where magma contacted ground water, producing plumes of steam and brownish ash. Based on data collected during an aerial survey the area of new lava was about 8.7 square kilometers and the erupted volume was an estimated 24 million cubic meters by 1706. The active part of the fissure was 2.4 km long by 1910 and continued to produce lava fountains. Lava flows from the fissure segment just S of Hagafell advanced S and W; part of the S flows advanced into a fissure, traveled beneath the surface, and emerged N of the barrier located NE of Grindavík. Lava flowed over Grindavík road towards Mt. Thorbjorn and along the barriers W of Grindavík, inundating part of Nesvegur road.

Activity significantly declined during 29-30 May and the ground surface in the Svartsengi area had subsided about 15 cm. Volcanic tremor stabilized and explosions were not detected since the afternoon of 29 May. IMO warned that the gas plume could impact areas downwind and had received reports of vog in several areas of the country during 29-31 May. During 30-31 May lava flows from the N end of the fissure flowed E, and flows W of Grindavík did not advance. According to a news report the effusion rate had slowed to around 50 cubic meters per second by 31 May. The lava flows minimally advanced and the flow field inflated. Areas of ponded lava were visible. Three cones had built up along the fissure and lava from two or three cones flowed SW and E during 2-3 June based on news articles. Two cones were active on 3 June and sometime during 0200-0300 on 4 June one of the cones ceased to be active. Lava advanced NW towards Sýlingarfell and then flowed N. An additional 4-6 cm of ground subsidence was detected at Svartsengi.

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), Iceland Monitor, Iceland Monitor