Explaining the origin of deposit-derived pyroclastic density currents

Abstract Pyroclastic density currents (PDCs) generated by the collapse of incandescent volcanic deposits represent a widespread but poorly understood hazard at active volcanoes. Their dynamics remain less constrained than those of dome- or column-collapse PDCs. In this study, we analyse two contrasting events at the Fuego and Arenal volcanoes using a two-dimensional limit-equilibrium slope stability modelling approach. The Fuego-type event reflects a purely gravitational end-member, whereby steep, hot deposits collapse without external triggering. In contrast, the Arenal-type event involves moderate internal pressurisation, likely related to shallow magma ascent or lava ponding. These processes can generate small-volume PDCs from spatter blankets and crater rims, features which are often overlooked in hazard scenarios, as well as from lava domes and flows, even in the absence of magma thrust. Our findings extend the recognised range of PDC-forming mechanisms and emphasise the importance of considering the mechanical failure of hot volcanic deposits when evaluating hazards, particularly at persistently active volcanoes with no obvious precursors to eruption.