The lava that erupted Wednesday, 3rd August, marks the first day of a new eruption at Fagradalsfjall and is chemically similar to magmas contributing to the eruption in 2021. The MgO content of rapidly quenched glass is 7.5% by mass, and the K2O/TiO2 ratio is 0.25 (see Figure 1).
The calculated eruption temperature is 1190-1200°C and the equilibrium pressure of the mineral assemblage in the magma is consistent with storage within a dyke in the upper crust (Figure 2). New arrival of magma from the mantle over the past months beneath Fagradalsfjall, as shown by geophysical measurements, could have led to the eruption. Daily monitoring by the geochemistry group at the University of Iceland will soon reveal more about the origins of this latest episode of volcanism on Reykjanes. Further information to follow.
Figure 1. The range in the K2O/TiO2 ratio of the 2021 Fagradalsfjall magma and the K2O/TiO2 ratio of the first sample of the 2022 Fagradalsfjall eruption. The figure shows that the first sample of the 2022 eruption has similar K2O/TiO2 ratio as the final lava of the 2021 eruption.
Figure 2. Backscatter electron image of a polished sample of the new lava. It shows a highly vesicular basaltic glass with microcrysts of plagioclase, olivine, clinopyroxene and Cr-spinel. The scale bar is 100 micron long.