A pyroclastic flow is the flow of volcanic ash, gases and fragments following a volcanic eruption. Ash is considered to be pyroclastic because it is a fine dust made up of volcanic rock. https://www.nationalgeographic.org/encyclopedia/pyroclastic-flow We also describe the eruption style and the deposits of different kinds of pyroclastic falls, flows and surges, based on studies of Quaternary volcanoes. The speed of these flows, as well as the extremely high … Pyroclastic rocks (derived from the Greek: πῦρ, meaning fire; and κλαστός, meaning broken) are clastic rocks composed of rock fragments produced by explosive volcanism and erupted as individual particles. Pyroclastic flows are a type of pyroclastic density current consisting of heterogeneous mixtures of hot volcanic particles and gas flowing due to gravity with a higher density than that of air. Basically, pyroclastic flows are fluidized masses of gases, rocks, and ash that can exit out of a volcano and travel away from the volcano across the land. They are incredibly hot and can travel faster than a moving vehicle in some cases. The following kinds of pyroclastic surge deposits (the general name for all types of low-concentration pyroclastic flows, named on the basis of origin and/or place in sequence), have been indentified: Surges are less dense, they move more quickly and can surmount topography such as hills and ridges. One of the most spectacular forms of pyroclastic deposit are the ignimbrites, deposits formed by the high-temperature gas-and-ash mix of a pyroclastic flow event. The materials in the flow can be heated from as low as 100 degrees all the way up 800 degrees Fahrenheit. Pyroclasts of different sizes are classified as volcanic bombs, lapilli, and volcanic ash. Pyroclastic flows originated in both ways at Mount St. Helens on May 18, but flows of mappable volume were of the latter type. Pyroclastic flows are a mixture of hot gas along with volcanic matter, like ash and rock fragments, she said. Pyroclastic flows. The individual rock fragments are known as pyroclasts.Pyroclastic rocks are a type of volcaniclastic deposit. Pyroclastic flow A pyroclastic flow is a ground-hugging avalanche of hot ash, pumice, rock fragments, and volcanic gas that rushes down the side of a volcano as fast as 100 km/hour or more. Pyroclastic flows are a very dangerous phenomenon that occur during some volcanic eruptions. The flows were entirely restricted to a small fan-shaped zone that flares northward from the summit crater. pyroclastic flow deposits has significant implications with respect to eruption and flow mechanics. In this introductory chapter on pyroclastic rocks we set out the differences between these three basic types of deposit. 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