ALBERT

Description: Stromboli is well-known for its persistent, low-intensity, ordinary activity, occasionally interrupted by more violent, paroxysmal events and intermediate-scale major explosions. While the feeding system of ordinary and paroxysmal activity is largely discussed in the literature, key parameters such as magmatic source, pre-eruptive dynamics and the associated timescales remain elusive for major explosions. This information, however, is fundamental for identifying potential precursory signals and improving existing early-warning systems as well as understanding the processes that control variable eruption magnitude and intensity at open-conduit basaltic volcanoes. The 19 July 2020 eruption ejected an important amount of juvenile, deep-sourced magma providing an excellent opportunity to investigate the role of the deep feeding system activated during high-intensity activity. While geophysical parameters place this eruption at the upper limit of major explosions, similar to small-scale 2003 and 2007 paroxysms, a detailed geochemical characterisation of melt inclusions, olivine and matrix glass integrated with gas measurements highlights important differences in the feeding system dynamics. Melt inclusion volatile contents suggest a ponding zone at ⁓9.5 km b.s.l. and the activation of a shallower zone at ⁓5–6 km b.s.l.. Pre-eruptive magma and degassing dynamics appear to be controlled by deep CO〈sub〉2〈/sub〉 fluxing and magma self-mixing. Olivine Fe-Mg diffusion modelling yields time constraints that are coherent with a change in CO〈sub〉2〈/sub〉/SO〈sub〉2〈/sub〉 ratios observed in the degassing plume, indicating a system perturbation ⁓20–25 days before eruption onset. The presented geochemical-petrological datasets, integrated with monitoring observations, provide a comprehensive framework for discussing the steady-state processes crucial for eruption forecast modelling.

Description: The 2021 hybrid Tajogaite eruption of Cumbre Vieja (La Palma) was mainly effusive, with 〉70% of volume erupted as lava and simultaneous explosive activity with variable eruptive styles (e.g., Strombolian, violent Strombolian, lava fountaining, ash-poor gas puffing) depositing a widespread tephra blanket. Tephra dispersal and grainsize features indicate violent Strombolian dynamics when field-based classification schemes are used. Statistical analyses of pulsatory activity indicate short-time fluctuations amongst the observed multiple eruptive styles, suggesting rapid gas segregation and high magma ascent rate modulating magma fragmentation and conduit dynamics distributed at the different vents. Pulsatory activity and variable eruptive style affected tephra sedimentation causing unsteady tephra ground accumulation across time. Various sedimentation processes were observed, including particle aggregation (especially in case of rainy atmospheric conditions) and different types of sedimentation features (e.g., lapilli waves, ash fingers). The tephra blanket, with a volume of ~2×10〈sup〉7〈/sup〉 m〈sup〉3〈/sup〉, was mostly dispersed NE-SW due to the complex regional and local wind patterns and was subdivided into three units and eleven layers that well correlate at different distances from the vent and agree with both seismic tremor data and lava emission rates. Grainsize distributions at individual locations are unimodal, with Mdf increasing and sorting decreasing with distance from the vents. Total grainsize distributions of selected layers, units, and the whole tephra blanket are unimodal with Mdphi values between -0.5 and 1.4 phi (1.4-0.4 mm). Evidence of the Tajogaite eruption dynamics highlight the challenges of risk and crisis management associated with long-lasting basaltic pulsatory hybrid eruptions.