Editing Pyroclastic flow (section)

{{Short description|Fast-moving current of hot gas and volcanic matter that moves away from a volcano}}
[[File:Mayon Volcano eruption at Daraga Church.jpg|thumb|Pyroclastic flows sweep down the flanks of [[Mayon Volcano]], [[Philippines]], in 2018]]
A '''pyroclastic flow''' (also known as a '''pyroclastic density current''' or a '''pyroclastic cloud''')<ref>{{cite book |last1=Branney |first1=Michael J. |last2=Kokelaar |first2=B. Peter |title=Pyroclastic Density Currents and the Sedimentation of Ignimbrites |date=2002 |publisher=Geological Society of London |isbn=978-1-86239-124-6 }}{{pn|date=January 2025}}</ref> is a fast-moving current of hot [[volcanic gas|gas]] and volcanic matter (collectively known as [[tephra]]) that flows along the ground away from a [[volcano]] at average speeds of {{convert|100|km/h|m/s mph|-1|abbr=on}} but is capable of reaching speeds up to {{convert|700|km/h|m/s mph|-1|abbr=on}}.<ref>{{Cite web|url=https://pubs.usgs.gov/gip/msh//pyroclastic.html|title=MSH Pyroclastic flow [USGS]|publisher=United States Geological Survey}}</ref> The gases and tephra can reach temperatures of about {{convert|1000|C|F|sigfig=2}}.

Pyroclastic flows are the deadliest of all [[volcanic hazard]]s<ref>{{Cite journal|last1=Auker|first1=Melanie Rose|last2=Sparks|first2=Robert Stephen John|last3=Siebert|first3=Lee|last4=Crosweller|first4=Helen Sian|last5=Ewert|first5=John|date=2013-02-14|title=A statistical analysis of the global historical volcanic fatalities record|journal=Journal of Applied Volcanology|volume=2|issue=1|pages=2|doi=10.1186/2191-5040-2-2|s2cid=44008872|issn=2191-5040|doi-access=free|bibcode=2013JApV....2....2A }}</ref> and are produced as a result of certain [[explosive eruptions]]; they normally touch the ground and hurtle downhill or spread laterally under gravity. Their speed depends upon the density of the current, the volcanic output rate, and the gradient of the slope.