A block and ash flow or block-and-ash flow is a flowing mixture of
volcanic ash and large (>26 cm) angular
blocks[1] commonly formed as a result of a
gravitational collapse of a
lava dome or
lava flow.[2] Block and ash flows are a type of
pyroclastic flow and as such they form during
volcanic eruptions.[3] In contrast to other types of pyroclastic flows, block and ash flows do not contain pumice[4] and the volume of block and ash flow deposits is usually small.[2] Block and ash flow deposits have densities in the range of 1600 to 2000 kg/m3, two to five times greater than ash fall deposits.[2] Some blocks in block and ash flow deposits may have thin and shiny coatings of carbon derived from
charcoal formed from vegetation trapped by the flow.[5]
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abcPyle, David M. (2015). "Chapter 13 – Sizes of Volcanic Eruptions". In
Sigurdsson, Haraldur (ed.). Encyclopedia of Volcanoes (2nd ed.). Amsterdam: Academic Press. pp. 257–264.
ISBN978-0-12-385938-9.