Magnetic characterisation of volcanic rocks from the Tajogaite eruption.

The Tajogaite eruption provides a recent example of the construction of a volcanic edifice and an opportunity to track the evolution of the volcano and its products. The eruption was active from 19 September to 13 December 2021, making its surface incursion into the Cumbre Vieja volcanic rift. Over the months, there were several eruptive vents that built a main edifice. Among its main products were tephritic and basanitic lava flows, some reaching the coast; pyroclastic materials near the cone, such as bombs; and ash ejection throughout the process.

The aim of this work is to study the mineralogical composition through the magnetic characterisation of the rocks. The lavas from the 2021 eruption have similar compositions, ranging from tephrites to basanites, emitted in the early and late stages of the eruption, respectively, with the former being richer in amphibole and the latter richer in olivine. Rocks emitted by the Tajogaite volcano are compared with those from other eruptions on the island, such as San Juan (1949) and Tacande (1480).

To this end, a methodology is employed which consists, firstly, of collecting field samples for magnetic characterisation. With the aid of a Vibrating Sample Magnetometer, the natural remanence of the samples, the first magnetisation curves and the hysteresis loops are measured.

An original contribution of this work is the use of a normalisation of the first magnetisation curves. Depending on their shape and changes in slope, compositional differences in the samples can be identified due to variations in their magnetic carriers. Therefore, we associate different curves with different rock compositions.