Updated earthquake density video added (uses satellite image as background). 12.04.2021
Geldingadalur – Where Are We at Now?
Since we last wrote, the new volcano at Geldingadalur has continued to erupt with a lava output rate between 5 m3 per second and 10 m3 per second, filling the Geldingadalur valley with more lava. The University of Iceland has confirmed that the early lava erupted has a magnesium content of 8.5%, a low titanium dioxide content and is more depleted in rare earth elements (low HREE to LREE ratio) than earlier historic lavas, indicating that it is a more primitive lava sourced from the lithospheric mantle at a depth of between 17 km and 20 km.
On 5 April 2021 at around midday, a new fissure opened up about 700 m north east of the original eruption site. The fissure, spotted by a sightseeing helicopter, was quickly confirmed by the RUV.is webcam monitoring Geldingadalur. Fortunately, no-one was in the vicinity at the time due to bad weather and sheer good luck; the site had been open to visitors at the time. The fissure is around 200 m long. Lava from the fissure is flowing into the Meradalir valley.
At around midnight on 6 April 2021, a second fissure opened up between the earlier fissure and the original eruption site. This had been preceded by a landslip earlier in the day. Lava from this fissure is now flowing into both the Geldingadalur and Meradalir valleys, linking the eruption sites. It is believed that the three eruption sites belong to the same fissure.
Unfortunately, one of the webcams set up by mbl.is to monitor the Geldingadalur cones was lost; its last image is shown below. We thank mbl.is for providing the webcam; we viewed its images with a lot of interest.
Like the original eruption site, neither fissure opening was heralded by an increase in seismicity in the immediate vicinity.
Seismicity Post the Initial Eruption
We have updated our earthquake plots for the period 19.03.2021 to 06.04.2021. We can confirm that there is very little earthquake activity in the vicinity of Geldingadalur. The fissures are not giving any seismic warning; seismic activity near Keilir dominates. It is perhaps surprising that magma has not made its way to the surface north east of Fagradalsfjall; does magma finds it easier to make its way through older fault-ridden Pleistocene rock that has not been covered in tougher historic lavas?
We have also tried our hand at making a video of the earthquake density plots by month from 2008 to 6 April 2021. Months are numbered from January 2008 (Month 1) to April 2021 (Month 160, which only has 6 days). If you make it all the way through, you will see that Fagradalsfjall has had several swarms, albeit much smaller than the current one. Enjoy!
As noted in earlier posts, for up-to-date advice and status, check out IMO or the Department for Civil Protection and Emergency, links below.
The Armchair Volcanologist
© Copyright remains with the author; all rights reserved, 2021.
Icelandic Met Office: https://en.vedur.is/ (English site)
Icelandic Met Office: https:// vedur.is/ (Icelandic site)
Reykjavik Grapevine: https://grapevine.is/