A pyroclastic flow with a mechanism that generates nuee ardente deposits of block and ash which are generated by dome collapse caused by a gas driven explosion. St. Helens, Skamania County, Washington August 7, 1980 n. pl. The speed of these flows, as well as the extremely high â¦ These mixtures of ash, lava blebs and broiling gas â¦ Define pyroclastic. A pyroclastic flow from Mayon in the Philippines, seen on September 23, 1984. Information and translations of pyroclastic flow in the most comprehensive dictionary definitions resource on the web. adj. Pumice flow. âThe pyroclastic deposits mainly consist of block-and-ash, blast, tephra fallout and secondary pyroclastic flow deposits.â âAnd they also say there's a potential danger from pyroclastic flows.â A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at velocities of 100 km/h (62 mph) on average but is capable of reaching speeds up to 700 km/h (430 mph). pyroclastic synonyms, pyroclastic pronunciation, pyroclastic translation, English dictionary definition of pyroclastic. nuée ardente eruption of Mt. Pyroclastic flow synonyms, Pyroclastic flow pronunciation, Pyroclastic flow translation, English dictionary definition of Pyroclastic flow. Definition of pyroclastic flow in the Definitions.net dictionary. Heavy debris falls rapidly from the sky and flows down the flanks of the volcano, mostly as pumice. Pyroclastic flows are the signature fireworks of the most explosive kinds of volcanic eruptions. Meaning of pyroclastic flow. âThe pyroclastic deposits mainly consist of block-and-ash, blast, tephra fallout and secondary pyroclastic flow deposits.â âAnd they also say there's a potential danger from pyroclastic flows.â On the margins of pyroclastic flows, death and serious injury to people and animals may result from burns and inhalation of â¦ Other pyroclastic flows result from the collapse of an eruption column, the vertical mass of debris and gas that jets above an explosive volcano vent. In fact, this type of flow is sometimes known as a âpumice flow.â Composed chiefly of rock fragments or particles of volcanic origin, such as pumice, obsidian, or volcanic ash. Pyroclastic flows vary considerably in size and speed, but even relatively small flows that move less than 5 km (3 mi) from a volcano can destroy buildings, forests, and farmland. What does pyroclastic flow mean? A pyroclastic flow with a mechanism involving the collapse of an eruption column. Soufriere type. Pyroclastic flow, the fast-moving hot gases, ash, and cinders expelled from a volcano. I've labeled the main parts of a pyroclastic, with the leading surge, main body and accompanying ash cloud. Pyroclastic flows are a very dangerous phenomenon that occur during some volcanic eruptions. A pyroclastic flow (also known scientifically as a pyroclastic density current ) is a fast-moving current of superheated gas and rock (collectively known as tephra), which reaches speeds moving away from a volcano of up to 700 km/h (450 mph).