Triggering and emplacement mechanisms of Pyroclastic Density Currents in basic volcanic systems.

Volcanic systems erupting mafic magmas are well known for producing predominantly effusive or weak explosive activity chiefly because of the physical and chemical properties of the magma itself. Even basic volcanoes in some cases can however give rise to extra-ordinary explosive phenomena with varying energy, producing occasionally also pyroclastic density currents (PDCs), which represent potential threat to populations living close the eruptive center or to visitors who frequent these volcanoes. Recently, this kind of phenomenon has been observed at several basic volcanoes, including Volcàn de Fuego (Guatemala), Stromboli (Italy) and especially Mount Etna (Italy), where several dozen PDCs have been observed and documented during the last decades. Although some of these PDCs have similarities with the classic processes characterizing volcanic systems erupting more evolved magmas, some of the mechanisms giving rise to the formation of these events have never been observed elsewhere and are still poorly studied. In this work we present an analysis of the triggering and emplacement mechanisms of the most important PDCs produced in recent years, using some case studies among the previously mentioned volcanoes. This type of approach could therefore be essential for a more detailed assessment of the hazards related to this type of phenomena, in order to reducing volcanic risk, especially in areas densely populated and/or frequented by tourists.