The 2023 lava of Fagradalsfjall

The rock is composed of vesicular glass and microphenocrysts and microlites of plagioclase, olivine, clinopyroxene and spinel (Fig. 1). These minerals commonly form glomerophyric intergrowths and some of them show chemical zonation. Macrocrysts (>1 mm in length) of plagioclase and olivine were also observed by naked eyes and under a stereomicroscope.

Fig.1: Backscattered electron image of a fresh lava sample collected on 10th of July 2023.

The tholeiitic basalt glass contains ~7.5 wt% MgO and 1.44 wt% of TiO2; with a K2O/TiO2 ratio of 0.26.

This is similar to the glass compositions determined for the 2022 lavas. The SO2 content of the degassed groundmass glass is 276+/-35 ppm, whereas the SO2 content in the undegassed melt inclusions is between 1900-2160 ppm.

Based on the chemical composition of the glass, we estimate a lava temperature of ~1190 °C (Putirka 2008), which is similar to the 2021 and 2022 lava temperatures.