CHAPTER 4.4 Pyroclastic Density Currents

Pyroclastic density currents (PDCs) are hot mixtures of gases and volcanic rock of diverse size, nature, or density, capable of flowing over long distances at velocities of tens to hundreds of kilometers per hour. They typically originate from the gravitational collapse of explosive eruption columns, lava domes or lava-flow fronts, unstable upper-flank material or from explosive lateral blasts. PDCs are produced from volcanic eruptions across many orders of magnitude in size and remain one of the deadliest volcanic hazards. In the last decade, significant progress in understanding PDC internal dynamics and associated hazards has been made thanks to major advances in numerical modeling and experimental studies. This chapter outlines what is known about the nature and behavior of PDCs based on observations, experiments, theory, and models; briefly reviews the main approaches used to characterize PDCs and their deposits; and finally highlights recent advances that constrain, test and enhance PDC models.