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Turrialba is an active volcano of the Cordillera Volcanica Central in Costa Rica, which is currently experiencing a renewal of the eruptive activity after ~150 years of eruptive quiescence. Because of its explosive eruptive records in the recent geological history and the proximity with the metropolitan area of San Jose, this volcano poses serious threats to the population and economy of the area. In this study, we investigated the andesitic products of an explosive event (VEI 4) that occurred at Turrialba volcano ~2 ka, which we referred to as “El Retiro” eruption. Results from field observations, textural and chemical analyses indicate that the El Retiro eruption was characterized by two main pulses separated by a low energy activity. The eruption was fed by a homogeneous andesitic magma batch that crystallized along a P-T path of 0.1–400 MPa and 1050–1145 °C. The vesicle number density of pumiceous clasts ranges between 107 and 108 cm−3, in agreement with previous data from subplinian eruptions. The magma batch underwent decompression rates and pre-fragmentation velocities of 0.40–0.95 MPa s−1 and 23–37 m s−1, respectively. A marked textural variability within each stratigraphic layer has been also observed. This potentially suggests a horizontal zonation of the magma column, a condition that may have induced velocity gradients and high viscosity contrasts in the conduit leading to magma fragmentation. The observed pulsating behavior translates into mass eruption rate fluctuations that can be related to changes in magma volatile contents. Further explosive eruptions with characteristics similar to those observed for El Retiro, cannot be excluded at Turrialba volcano. This denotes the importance of investigating eruption dynamics at the conduit, providing key information to rigorously assess the volcanic risk in populated areas.

Southern Italy is a most active tectonic and volcanic setting comprising active (Stromboli, Vulcano) or dormant (Lipari) volcanic islands in the Aeolian Arc, and the majestic Etna volcano (together with the Campanian volcanoes). They have attracted the attention of a great number of volcanologists and can be rightfully considered the cradle of the scientific discipline of Volcanology. In the Aeolian Arc, the main features are the incessant and rhythmic Strombolian exlosive activity of Stromboli and the Sciara del Fuoco collapse, together with the deposits of historical Vulcanian eruptions of Vulcano and its present-day intense fumarolic activity. The well-known Rocche Rosse obsidian lava flow and Mt. Pilato pumice are the traces of the Middle Ages activity of Lipari. On Etna, the geology of the valle del Bove depression and the summit craters and NE-Rift, and the 2001, 2002-03 and the 2011-2017 eruptive fissures and lava flow fields give an idea of the variability of its eruptive scenarios. The spectacular geology of these volcanoes and the INGV real-time monitoring network are the bases to discuss the main aspects of volcanic hazard and risk mitigation in case of future eruptions in a highly-urbanized territory characterized by intense tourism exploitation during the summer.