The eruption on the Reykjanes Peninula north of Fagradalsfjall continues with little changes. Activity is concentrated now at a single vent where the original spatter rampart is growing into a small cone, breached to the south where a lava river comes out, feeding the active flow field south of the vents.
Ground deformation observations
The Icelandic Met Office (IMO) published a new satellite-based radar interferogram covering the period from 27 June to 12 July 2023 (attached). It „shows ground deformation leading up to and during the first two days of the eruption. Each coloured fringe cycle represents 1.55 cm of deformation in the satellite‘s line-of-sight.
In relation to the dike intrusion, over 50 cm of extensional motion is observed in both the NW and SE directions (~ 1 m of outward movements in total across the interferogram). These outward movements occur perpendicular to the axis of the dike, and represent expansion to the NW and SE, in response to magma inflow into the dike. As was reported yesterday, GPS observations since eruption onset show that deformation is returning to background suggesting balance between inflow of magma and outflow in the eruption. At the same time seismicity has decreased significantly supporting this interpretation.“
Rising and decreasing tremor
IMO also published a graph showing the evolution of volcanic tremor before and during the eruption, which follows a typical pattern: spikes during the buildup mainly due to earthquakes that reflect magma pushing its way into fissures when rock underground is fractured, high levels of tremor during the initial phase and slowly declining tremor while the eruption continues and flow rates balance off with magma supply while at the same time the conduits become smoothed out and pose less obstacles.
„Since the eruption began Monday afternoon, July 10th, around 300 earthquakes have been recorded on the Reykjanes Peninsula. Most of the earthquakes have been below 2.0 in magnitude, but two have been measured larger, they were 2.0 and 2.1 in magnitude. This image below shows the evolution of the eruption over the last three days. Before the eruption, tremors are most noticeable on the graph. The unrest can be seen rising rapidly from 3pm on Monday, July 10, and peaked around 9pm.
The tremor graph shows tremor at three different frequencies, and it is clearly seen that the eruption tremor is greatest at the highest frequency, 2-4 Hz. Now that the eruption has begun, it can be expected that the seismic activity in the area will continue to decrease.“
(source: IMO)
