Block and ash flow

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Outcrop of a block and ash flow in the Tschicoma Formation, New Mexico, US

A block and ash flow or block-and-ash flow is a flowing mixture of

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]

References

  1. ^ "Glossary - Block and ash flow". volcanoes.usgs.gov. United States Geological Survey. Retrieved 22 October 2018. Flow of ash and angular rock fragments larger than 26 cm or 10 in.
  2. ^
    ISBN 978-0-12-385938-9
    .
  3. doi:10.1016/S0377-0273(98)00128-0
    .
  4. ^ "Block-and-ash flow deposit or lithic breccia?". Sandsatlas. Retrieved October 22, 2018.
  5. doi:10.1017/S0016756808005359
    .
  6. ^ "Block-and-ash flow deposits". Sandsatlas. Retrieved October 22, 2018.


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