Английская Википедия:Block and ash flow
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]
Volcanoes known for their production of block and ash flows since the 1990s include Mount Unzen in Japan, Mount Merapi in Java and Soufrière Hills in the Lesser Antilles.[6]
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