pyroclastic flow UK /paɪ.ɹə(ʊ)ˌklæ.stɪk ˈfləʊ/US /ˈpaɪ.ɹoʊ.klæ.stɪk floʊ/ noun1 •A dense flow of volcanic ash, dust, rocks and debris that cascades at high speed down the slope of a volcano during an eruption. formspyroclastic flows
