pyroclastic flow

plural pyroclastic flows

1. countablegeographyA dense flow of volcanic ash, dust, rocks and debris that cascades at high speed down the slope of a volcano during an eruption.

   Most of the material was erupted in the most dangerous way as ‘pyroclastic flows’: incredibly hot volcanic fragments all buoyed up with gas that can travel fasted than a speeding car in pulse after pulse.

   2011, Richard Fortey, The Earth, Folio Society, page x

   Synonyms: pyroclastic density current, PDC, pyroclastic surge

2. uncommonuncountablenatural sciencesUsed other than figuratively or idiomatically: see pyroclastic, flow: flow (uncountable) of pyroclastic particles.

   Viscous debris flow is different not only from inertial debris flow but also from granular flow, pyroclastic flow and snow avalanche, because the effect of inelastic collision of particles does not play an important role in viscous debris flow.

   2001, T. Takahashi, “Mechanics and simulation of snow avalanches, proclastic flows and debris flows”, in W.D. McCaffrey, B.C. Kneller, and J. Peakall, editors, Special Publications of the International Association of Sedimentologists, volume 31: Particulate Gravity Currents, Blackwell Science, page 39