Tilling, Robert I. Branch of Igneous and Geothermal Processes, U.S. Geological Survey, Menlo Park, California.
Last reviewed:December 2019
- Fall processes and deposits
- Flowage processes and deposits
- Related Primary Literature
- Additional Reading
Rocks formed by the accumulation of fragmental volcanic materials (also called pyroclasts) ejected during explosive eruptions. Pyroclasts can vary widely in origin, fragment size and shape, composition, texture, structure (such as their arrangement in the resulting deposit) and other properties (see table). Despite such differences, all pyroclastic materials and the great variety of pyroclastic rocks they form share a common, unifying attribute—all are produced by explosive volcanic activity. Pyroclastic deposits are included under a broader category of volcaniclastic deposits, comprising all fragmented volcano-derived material. In some cases, the explosive fragmentation is caused by the interaction of water with hot volcanic ejecta, producing hydrovolcanic materials, which are commonly regarded as pyroclastic sensu lato and will be discussed as such. See also: Caldera; Pyroclast; Volcano
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