Destructiveness of pyroclastic surges controlled by turbulent fluctuations

Abstract

Pyroclastic surges from volcanoes can be lethal hazards that are capable of obliterating reinforced buildings. However, to date, there are no measurements inside these currents to quantify the dynamics of this important hazard process. Here we show, through large-scale experiments and the first field measurement of pressure inside pyroclastic surges, that dynamic pressure energy is mostly carried by large-scale coherent turbulent structures and gravity waves. These perpetuate down-current as c. 1–20 successive high-pressure pulses per minute, with pressure maxima that exceed mean values traditionally estimated for hazard assessments. This discovery, which is also applicable to powder snow avalanches, explains the destructiveness of real-world flows and necessitates a re-evaluation of hazard models that aim to forecast and mitigate volcanic hazard impacts globally.