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Geldingadalir Eruption on the Reykjanes Peninsula

The eruption that started March 19th ein the Geldingadalir valley at Fagradalsfjall on the Reykjanes Peninsula of Iceland is the first to occur within the area since the year 1240. No one can predict for how long it will proceed, but it has been found that the lava is rather hot, or between 1180-1190°C, as can be seen here: https://www.mbl.is/frettir/innlent/2021/03/22/likist_dyngjugosbergi/

The lava is therefore of the category found in shield volcanoes. Therefore the possibility that this eruption will go on for some time can not be ruled out. The crater of Thrainsskjoldur (Þráinsskjöldur) is found nearby, a large shield volcano covering the central parts of the peninsula. Now we consider this as the smallest eruptions we have seen in Iceland. If this is really an effusive eruption of ‘shield volcano category’, it surely comes as a surprise.

The dyke of Geldinigadalir eruption.

The dyke extends about 8 km over the theoretical area of the seismic zone as extended from South Iceland Seismic Zone over the Reykjanes Peninsula, bending towards the Reykjanes Ridge. It is assumed according to the model that the main part of magma is originated from NW, and when the dyke propagates to the SW, it encounters the division line of the polygon.

The different composition of this lava compared with the lavas erupted around 1000 years ago, can be explained according to this model with influx through the ductile mantle (below the brittle crust) from the NW division line of the Reykjanes polygon, reaching underneath the dyke into a conduit leading to the eruption site at Geldingadalir.

The material of the dyke might have propagated from the NW, and outflow could be found into the mantle at the SW end of the dyke. At least, no clue of either depletion or accumulation of magma within the earth is being measured for the moment.

The position of eruption is marked here: https://www.mbl.is/frettir/innlent/2021/03/19/upptok_gossins_eru_i_geldingadal/

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