Friday seminars of Institute of Earth Sciences, August 28th 2026 - Helena Albert (Professor in volcanology), a visiting researcher from the University of Barcelona

Abstract

Crystals carried by erupted magmas preserve textural and compositional evidence of the processes experienced during magma storage and transport. Petrological studies allow us to identify crystal populations and to distinguish between growth, resorption, magma mixing and the remobilisation of previously stored crystals. Thermobarometric calculations further constrain the depths and temperatures at which these processes occur, providing a framework for reconstructing the architecture and evolution of the magmatic plumbing system. Where suitable compositional gradients are preserved, diffusion modelling provides an additional temporal constraint on the recorded processes. These timescales can then be compared with seismic, geodetic and geochemical monitoring signals to investigate the relationships between magma dynamics, volcanic unrest and changes in the eruptive behaviour.

I illustrate the range of processes recorded by crystals using four complementary case studies. At Parícutin volcano (Michoacán-Guanajuato Volcanic Field, Mexico), olivine crystals from the earliest tephra display cyclic Fo, Ni and P zoning generated by strong thermochemical gradients during dike propagation. More than half of the calculated timescales are shorter than 2 days, with some as short as 0.1 day, indicating rapid magma ascent. The evolution of the zoning patterns through the eruptive sequence records a transition from unstable, convective transport during dike opening to more sustained magma flow before the change from explosive to predominantly effusive activity.

At Puig Jordà volcano (Garrotxa Volcanic Field, Spain), olivine and clinopyroxene textures and compositions challenge the conventional interpretation of direct magma ascent from the mantle in the area. Resorbed crystal cores, reverse zoning and mineral overgrowths indicate that newly ascending magma incorporated crystals from previously emplaced and partly crystallised magma batches. Thermobarometric results suggest rapid ascent from a deep zone at 900–1200 MPa, followed by interaction with magma pockets located at 600–900 MPa and a final stage at approximately 120 MPa. This multi-level architecture demonstrates that arrested intrusions and transient magma storage may occur even in volcanic fields traditionally interpreted as being fed by direct magma ascent.

The 2021 Tajogaite eruption (La Palma, Canary Islands) provides an opportunity to integrate the crystal record with continuous geophysical and geochemical monitoring. Olivine zoning, mineral and whole-rock chemistry, diffusion timescales, seismicity, deformation and gas data identify at least three pre-eruptive intrusions that progressively reactivated the system. A final intrusion, recorded 10–30 days before the eruption, triggered magma ascent, whereas subsequent syn-eruptive injections influenced magma composition and eruptive intensity. During the second half of the eruption, olivine diffusion timescales and recurrent deformation pulses indicate a transition from magma recharge and outflow to transient shallow storage.

Four olivine compositional populations and their normal and reverse zoning patterns from the historical Siete Fuentes, Fasnia and Arafo eruptions on Tenerife (1704-1705) record successive interactions between magma batches stored at different levels. Diffusion modelling identifies an initial mixing event approximately 1 year before eruption, a second event involving more mafic magmas less than 2 months before eruption, and final magma transfer, mixing and ascent during the preceding 2 weeks. Historical accounts of felt seismicity record only this final stage, demonstrating that the crystal record can extend the reconstructed unrest history beyond the signals documented at the surface.

Together, these four case studies reveal a continuum of processes ranging from stalled intrusion and multi-level storage to dike opening, rapid ascent, syn-eruptive recharge and transient shallow storage development. Their integration supports a conceptual model in which early intrusions may stall and generate transient magma pockets, progressively modifying the thermal and rheological state of the crust. Subsequent dikes can intercept and remobilise these magma bodies, facilitating magma transfer towards the surface. Although the duration and expression of unrest vary among volcanic fields, the combined petrological and monitoring records identify recurring stages operating over timescales from years and months to weeks, days and hours. Establishing the processes recorded by crystals, their spatial distribution within the plumbing system and, where possible, their timing is therefore essential for interpreting volcanic unrest and anticipating changes in monogenetic eruptive activity.

All are welcome.