Watch CineCalidad. Pyroclastic flows (also known as a pyroclastic cloud or pyroclastic wave) are the devastating result of some volcanic eruptions. They are fluid bodies, composed of hot gas and pyroclasts (gray and stone) that can travel at speeds of up to 160 km per hour. In this case, the eruption is Cinema Marginal and the pyroclastic flows are called Ozualdo R. Candeias.