4D paleomagnetic and rock magnetic properties of the 2021 and 2022 Fagradalsfjall eruption products, Iceland

Understanding how paleomagnetic and rock magnetic properties vary as a function of time and space is important for acquiring reliable information about the past Earth’s magnetic field. In basalts the magnetic properties are controlled by Fe-Ti oxides precipitating from the magma. The fraction, type, and mineral and magnetic grain size and shape are determined by a complicated multiphase process through the history of the lava or tephra. The deep magmatic conditions with melt composition, temperature, pressure, and oxygen fugacity are the starting point influencing the initial magnetic mineralogy and the matrix surrounding it. The final stage of crystallization is controlled also by syn-eruptive and emplacement conditions such as viscosity, cooling rate, incorporation of water, eruption style and atmospheric oxidation. Lastly, regardless of the natural environment the magnetic mineralogy is bound to further suffer from some degree of chemical alteration and low temperature oxidation. Therefore, the magnetic properties vary considerably even within the same cooling unit, and where one samples can affect the successfulness of paleomagnetic or paleointensity study. Historical eruptions like Fagradalsfjall 2021 and 2022 provide ideal locations for case studies since we know exactly not only the direction and strength of the magnetic field, but also the geochemical properties of the lavas due to near real time analysis of the eruption products. Here we present the magnetic properties of the Fagradalsfjall 2021 and 2022 eruption products. We collected samples during the eruptions as a function of time from the fast cooled materials, such as samples from the naturally fast cooled flow tops, manually quenched samples from the molten lava, and tephra. After eruptions seized and it was safe to work on the lava, we drilled over 100 lava samples from various locations and morphologies. These samples were subjected to a battery of measurements possible at University of Iceland Paleomagnetism Laboratory slightly varying depending on the type of sample such as bulk susceptibility, low field susceptibility vs temperature, hysteresis properties, backfield coercivity distribution, First Order Reversal Curves, alternating field, and thermal demagnetization. With our preliminary results we show how the magnetic properties vary a) between different types of volcanic products, b) across the lava fields and their multiple morphologies, c) as a function of depth, and d) as a function of time from the beginning of the eruption for the rapidly quenched materials.