Chapter 5 - Pyroclastic Density Current Hazards and Risk

Abstract

Pyroclastic density currents (PDCs) represent a formidable challenge for volcanology. This is true in terms of scientific understanding of their dynamics, and also in terms of assessment of their hazard and risk. These phenomena occurred in the famous, lethal 79 AD Pompeii eruption of Mt. Vesuvius, although recognition in “modern” times dates from observations made in 1902 at Montagne Pelée. Major progress in understanding has developed in the last few decades, due both to direct observations and improved modeling capability. Currently, PDC generation and propagation mechanisms are deeply investigated by field reconstructions, and also via detailed experimental and modeling studies. In this chapter we review the current status of knowledge on the dynamics of PDCs, and highlight the key processes and impacts as revealed by recent eruptive events. Some current approaches and modeling studies aimed at PDC hazard assessment are then illustrated, with specific reference to short-to-medium term hazard assessments carried out at the Soufriere Hills volcano at Montserrat (West Indies, UK), and to long-term assessments at the high-risk Vesuvius volcano and Campi Flegrei caldera (Italy). We conclude this review with remarks on the current and evolving state of knowledge of this dangerous volcanic phenomenon, and implications on the challenges for hazards mitigation. Significant limitations exist in our current ability to accurately forecast zones at risk from some PDCs, and in practice, hazard evaluations require cautious good judgment and not over-reliance on computations based on oversimplified algorithms and inputs.