IMO reported that the eruption that began on 29 May near Sundhnúk, NE of Sýlingarfell within the Reykanes volcanic system, decreased over a few days and then ended on 24 June, with the eruption spanning a total of 24 days. According to a news article, earlier in the week lava flowed mostly N along Sýlingarfell and thickened in some areas, rising higher than the earthen barriers N of Svartsengi; on 18 June lava flowed over the barrier between Sýlingarfell and Grindavíkurvegar, prompting workers to try to stop the advancement of the lava by spraying water on the flows as an experimental defense. By 20 June lava was flowing over the barrier in three places. Firefighters sprayed water on the lava causing steam-and-gas plumes to rise from the slow-moving flows. Large machinery was also utilized to move dirt and strengthen the barrier. The westernmost flow that overtopped the barrier was the most active and continued to advance and thicken during 20-21 June. Tremor levels decreased, indicating that the eruption was decreasing, though a decreasing rate of uplift in the Svartsengi area continued to be recorded in GPS data.

Images from a drone overflight conducted during the morning of 21 June by Almannavarnadeild ríkislögreglustjóra (National Commissioner of the Icelandic Police and Department of Civil Protection and Emergency Management) showed decreased activity at the main crater. Areas of incandescent lava in the crater were visible; lava flows from the crater were not seen, though flows through lava tubes may have been active. Sulfur dioxide emissions were very low. During a drone survey around noon on 22 June no activity in the crater was visible, indicating that the eruption had ceased. Additionally, tremor levels had decreased to levels similar to those recorded before the eruption began. On 24 June IMO noted that still-molten lava continued to advance over the barrier at Sýlingarfell and on the lava field N of the barrier. At 1410 on 25 June IMO lowered the Aviation Color Code to Yellow (the second lowest level on a four-color scale).

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)