IMO reported possible magma accumulation beneath Reykjanes, centered along the plate boundary below the Svartsengi fissure system, just W of Thorbjorn. Deformation began on 21 January and was unusually rapid, with the rate of inflation occurring at 3-4 mm per day (3 cm total by 29 January), as detected by InSAR and continuous GPS data. Magma accumulation, if that was causing the inflation, was small with an estimate volume of 1 million cubic meters, at 3-5 km depth. Deformation on the Reykjanes peninsula had been measured for three decades with no previously comparable signals.

An earthquake swarm accompanied the deformation, just E of the center of the inflation. The largest earthquakes were M 3.6 and 3.7, recorded on 22 January, and felt widely on the Reykjanes peninsula and all the way to Borgarnes region. Earthquake swarms are relatively common, though coupled with deformation caused IMO to raise the Aviation Code to Yellow on 26 January. The swarm was declining by 26 January. On 29 January IMO stated that data showed continuing uplift and the earthquake swarm was ongoing.

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.

Source: Icelandic Meteorological Office (IMO)