Rosa Anna Corsaro

Coupled textural and compositional characterization of basaltic scoria: Insights into the transition from Strombolian to fire fountain activity at Mount Etna, Italy

Strombolian and fire fountain activities represent a common expression of explosive basaltic eruptions. However, the transition between these two eruptive styles and their source mechanisms are still debated. We use textural and compositional studies to characterize pyroclastic material from both the Strombolian and Hawaiian-style fire fountain phases of the January–June 2000 Etna activity. We find that basaltic scoria presents distinctive textural and compositional features that reflect different modes of magma vesiculation and crystallization in the two eruptive regimes. Overall, magma that forms Strombolian scoria is far more crystallized, less vesicular, and more evolved, indicating strong volatile depletion and longer residence time before being erupted. Fire fountain scoria indicates a fast-rising magma with evidence of moderate syneruptive volatile exsolution. The new textural and compositional data set is integrated with previous volcanological and geophysical investigations to provide further insights into the dynamics of fire fountains, and to frame the transition from Strombolian explosions to fire fountain activity into a model that may apply to future eruptions at Mount Etna as well as other active basaltic volcanoes.

Dynamics of Magmas at Mount Etna

The mineralogical, petrographic, geochemical and isotopic data collected in recent years on the entire Etnean succession have been examined in order to recognize the most important compositional variations and to relate them to important changes in parameters that control the genesis and transport of magmas. Building on this data set, the most important ideas on magmatic processes and magma dynamics in the plumbing system of Mt.Etna are summarized. Interpretative models presented by various research teams indicate that the geochemical characters of Etnean magmas have changed and are still changing. Moreover, even if depth of formation, melting processes and first stages of differentiation of Etnean magmas are still largely unconstrained, the sources and compositional evolution are influenced by the complicated geodynamic environments in which the volcano developed. Multi-stage, polybaric, fractional crystallization of phenocryst-forming minerals is the main process responsible for the differentiation of Etnean magmas, but at shallow depths, contamination, mainly by interaction with fluids or rocks belonging to the sedimentary basement, plays an important role. Both petrologic and geophysical data demonstrate that magma ascent and depth of magma storage are largely controlled by buoyancy, and exclude the present-day occurrence of large active crustal reservoirs. Finally, recent studies of Etnean explosive activity show the most violent eruptions have been fed by both evolved and pristine magmas. Consequently the pre-eruptive volatile content, devolatilisation and magma degassing rate during ascent are processes that must be adequately considered to evaluate the dynamics of magmas within this volcano and their relationship to eruptive style.

Paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna during the last 225 ka inferred from the volcanic succession of the ‘Timpe’, Acireale, Sicily

Abstract The tectonic escarpments locally known as ‘Timpe’ cut a large sector of the eastern flank of Etna, and allow an ancient volcanic succession dating back to 225 ka to be exposed. Geological and volcanological investigations carried out on this succession have allowed us to recognize relevant angular unconformities and volcanic features which are the remnants of eruptive fissures, as well as important changes in the nature, composition and magmatic affinity of the exposed volcanics. In particular, the recognition in the lower part of the succession of important and unequivocal evidence of ancient eruptive fissures led us to propose a local origin for these volcanics and to revise previous interpretations which attributed their westward-dipping to the progressive tectonic tilting of strata. These elements led us to reinterpret the main features of the volcanic activity occurring since 250 ka BP and their relationship with tectonic structures active in the eastern flank of Etna. We propose a complex paleo-environmental and volcano-tectonic evolution of the southeastern flank of Mt. Etna, in which the Timpe fault system played the role of the crustal structure that allowed the rise and eruption of magmas in the above considered time span.

Multidisciplinary investigation on a lava fountain preceding a flank eruption: The 10 May 2008 Etna case

A multidisciplinary approach integrating a wide data set ranging from bulk rock compositions of the erupted products to volcanic tremor, long-period events, and tilt and gravity signals is used to investigate the source depth and magma dynamics of the 10 May 2008 lava fountain at Southeast crater (SEC) of Mount Etna. The investigation was undertaken in the framework of the previous 2007 explosive activity as well as the subsequent effusive eruption beginning 13 May 2008 and lasting up to July 2009. All the data concur in indicating that the 10 May lava fountain was generated by the fragmentation of a foam layer trapped at the top of a shallow reservoir, about 1500–1700 m below the summit of SEC. The shift from the episodic strombolian/lava fountain activity occurring in 2007 at SEC to the more powerful 10 May 2008 lava fountain is explained by the intrusion of a new more primitive magma into the shallow reservoir. Data also indicate that an attempted magma intrusion east of the summit area occurred during the 10 May fire fountain. This event caused the fracturing and weakening of the surrounding rocks and created a preferential pathway for the penetration of the magma that, only 3 days later, started to feed the 2008–2009 effusive eruption.

Textural evidence of peperites inside pillow lavas at Acicastello Castle Rock (Mt. Etna, Sicily)

Globular and microglobular peperites, with mingled sediment in millimetric to decimetric domains, are described from inside pillow lavas at Acicastello Castle Rock, Mt. Etna, Sicily for the first time. The peperites now comprise basalt and minor remnants of fine-grained detrital material, with smectite and zeolite crystallised during late hydrothermal activity. We propose that peperites formed when the magma, ascending towards the surface, intruded and intermixed with the unconsolidated wet Pleistocene bluish marly clays of the substrate. Subsequently they were transported by the uprising magma from the source region towards the surface, where they are preserved in pillow lavas.