Fig. 1: Synthesizing pyroclastic density currents and dynamic pressure measurements in large-scale experiments.

a The time-variant flow structure of the experimental PDC during channel confined propagation along a proximal measurement profile, which is located at 1.8 m downstream from impact of the hot mixture of volcanic material and air with the channel. The height-time kymograph is obtained by the stacking of vertical columns of pixels recorded by a high-speed camera at the static observer location. Pixel brightness correlates positively with, both, bulk flow particle volume concentration and the abundance of highly reflective coarse-grained pumiceous glass shards and plagioclase crystals. At this location, the density current structure is fully developed comprising a leading head with a wake in its rear and a trailing density current body. The density current tail region is not shown. b Lateral view of the frontal c. 7 m of the advancing experimental PDC across the unconfined distal runout section approximately 1.5 m before buoyancy reversal. The red line shows the time-variant height of the upper flow boundary. c Snapshot of the front of the experimental PDC approaching one of the wing-shaped vertical profiles of dynamic pressure sensors. The shape of the wings is designed to reduce flow detachment and formation of a turbulent wake behind the profile. The sensing elements of the piezoelectric dynamic pressure sensors protrude, upstream from the wing, into the approaching density current.