5. Conclusions
Near real-time photogrammetric monitoring of the eruption at Fagradalsfjall 2021 was performed using a combination of satellite and airborne stereoimages as a part of the response to the event. This provided essential eruption parameters such as volume and effusion rate, as well as the maps distributed to the public, the Civil Protection, rescue teams, and the tourism industry.
By September 30, 2021, 32 surveys have been performed. Currently, the lava flow-field covers 4.8 km2 and the estimated bulk volume (including vesicles and macroscale porosity) is 150 × 106 m3, yielding a mean effusion rate (from the beginning of the eruption start) of 9.5 ± 0.2 m3/s.
The lava pathways and lava advancement were very complex and changeable as the lava filled and spilled from one valley into another and short-term prediction of the timing of overflow from one valley to another proved challenging. Analysis of thickness maps and thickness change maps show that the lava transport into different valleys varied up to 10 m3/s between surveys as lava transport rapidly switched between one valley to another.
Compared to recent Icelandic eruptions, the evolution of the effusion rate is very unusual, having a very low and stable effusion in phase 1–2 and increasing effusion in phase 3. This behavior may be due to widening of the conduit by thermal erosion with time, and not controlled by magma chamber pressure as is most common in the volcanic zones of Iceland.