Pyroclastic density currents at mafic volcanic systems: insights from four decades of observations at Mount Etna volcano, Southern Italy

Pyroclastic Density Currents (PDCs) have long been considered rare in mafic volcanic systems. However, over the past century, such events have been widely documented at several mafic volcanoes worldwide and, in particular, at Mount Etna, where more than fifty occurrences have been recorded in the last four decades. This study provides a comprehensive review of PDC events at Etna since 1986, assessing the diversity of processes responsible for their generation. The examined events reveal that PDCs at Etna may originate from multiple mechanisms, including instantaneous collapse of the pyroclastic mixture, gravitational remobilization of freshly deposited hot tephra, partial flank failure of pyroclastic cones, and explosive interactions between lava and snow or wet substrates. Several episodes also illustrate the superimposition of distinct triggering processes, highlighting the complexity of PDC initiation at this volcano. The overall increase in PDC frequency observed over recent decades is mainly related to the intensification of summit paroxysmal activity and the rapid growth and mechanical destabilization of the Southeast Crater, the most active of the four summit craters of Mount Etna. Although many PDCs showed minor runouts, larger events have reached runouts of 2–3 km in recent years, occasionally impacting some of the most frequented areas in the summit region of the volcano. These observations demonstrate that PDCs represent a non-negligible hazard at Etna, particularly in sectors frequently visited by tourists and hikers, where the sudden onset and rapid propagation of even small-volume PDCs may pose a significant threat.