Editing Pyroclastic flow (section)

==Size and effects==
[[File:PyroclasticFlow.jpg|thumb|Building remnant in Francisco Leon destroyed by pyroclastic surges and flows during eruption of [[El Chichon]] volcano in Mexico in 1982. Reinforcement rods in the concrete were bent in the direction of the flow.]]
[[Image:Pyroclastic Flow St. Helens.jpg|thumb|A scientist examines pumice blocks at the edge of a pyroclastic flow deposit from [[Mount St. Helens]]]]
[[File:Pompeii Garden of the Fugitives 02.jpg|thumb|The casts of some victims in the so-called "Garden of the Fugitives", [[Pompeii]]]]
Flow volumes range from a few hundred cubic meters to more than {{convert|1000|km3|cumi}}. Larger flows can travel for hundreds of kilometres, although none on that scale has occurred for several hundred thousand years. Most pyroclastic flows are around {{convert|1|to(-)|10|km3|cumi|spell=in|frac=4}} and travel for several kilometres. Flows usually consist of two parts: the ''basal flow'' hugs the ground and contains larger, coarse boulders and rock fragments, while an extremely hot [[ash plume]] lofts above it because of the turbulence between the flow and the overlying air, admixing and heating cold atmospheric air causing expansion and convection.<ref>Myers and Brantley (1995). Volcano Hazards Fact Sheet: Hazardous Phenomena at Volcanoes, USGS Open File Report 95-231</ref> Flows can deposit less than 1 meter to 200 meters in depth of loose rock fragment.<ref>{{Cite web |title=Pyroclastic flows move fast and destroy everything in their path {{!}} U.S. Geological Survey |url=https://www.usgs.gov/programs/VHP/pyroclastic-flows-move-fast-and-destroy-everything-their-path |access-date=2024-09-12 |publisher=United States Geological Survey}}</ref>

The [[kinetic energy]] of the moving cloud will flatten trees and buildings in its path. The hot gases and high speed make them particularly lethal, as they will incinerate living organisms instantaneously or turn them into carbonized fossils: 
* The [[Ancient Rome|Ancient Roman]] cities of [[Pompeii]] and [[Herculaneum]] (now in Italy), for example, were engulfed by pyroclastic surges of [[Mount Vesuvius]] in AD 79 with many lives lost.<ref>{{cite book |last=Weller |first=Roger |title=Mount Vesuvius, Italy. |publisher=Cochise College Department of Geology |year=2005 |access-date=15 October 2010 |url=http://skywalker.cochise.edu/wellerr/students/mount-vesuvius2/vesuvius.htm |archive-url=https://web.archive.org/web/20101023185623/http://skywalker.cochise.edu/wellerr/students/mount-vesuvius2/vesuvius.htm |archive-date=23 October 2010 |url-status=dead }}</ref>
* The 1902 eruption of [[Mount Pelée]] destroyed the [[Martinique]] town of [[Saint-Pierre, Martinique|St. Pierre]]. Despite signs of impending eruption, the government deemed St. Pierre safe due to hills and valleys between it and the volcano, but the pyroclastic flow charred almost the entirety of the city, killing all but three of its 30,000 residents.{{citation needed|date=July 2020}}
* A pyroclastic surge killed [[volcanologist]]s [[Harry Glicken]] and [[Katia and Maurice Krafft]] and 40 other people on [[Mount Unzen]], in Japan, on June 3, 1991. The surge started as a pyroclastic flow and the more energised surge climbed a spur on which the Kraffts and the others were standing; it engulfed them, and the corpses were covered with about {{convert|5|mm|in|frac=8|abbr=on}} of ash.<ref>Sutherland, Lin. Reader's Digest Pathfinders Earthquakes and Volcanoes. New York: Weldon Owen Publishing, 2000.</ref>
* On June 25, 1997, a pyroclastic flow travelled down Mosquito Ghaut on the [[Caribbean]] island of [[Montserrat]]. A large, highly energized pyroclastic surge developed. This flow could not be restrained by the Ghaut and spilled out of it, killing 19 people who were in the Streatham village area (which was officially evacuated). Several others in the area suffered severe burns.{{citation needed|date=July 2020}}

===Interaction with water===
Testimonial evidence from the [[1883 eruption of Krakatoa]], supported by experimental evidence,<ref name=Freundt2003>{{cite journal
  | title = Entrance of hot pyroclastic flows into the sea: experimental observations
  | journal = [[Bulletin of Volcanology]] 
  | volume = 65
  | pages = 144–164
  | year = 2003
  | bibcode = 2002BVol...65..144F
  | last1 = Freundt
  | first1 = Armin
  | issue = 2 
 | doi = 10.1007/s00445-002-0250-1| s2cid = 73620085 
 }}</ref> shows that pyroclastic flows can cross significant bodies of water. However, that might be a [[pyroclastic surge]], not flow, because the density of a gravity current means it cannot move across the surface of water.<ref name=Freundt2003/> One flow reached the [[Sumatra]]n coast as far as {{convert|48|km|nmi|frac=2|abbr=off}} away.<ref>Camp, Vic. "KRAKATAU, INDONESIA (1883)". How Volcanoes Work. Department of Geological Sciences, San Diego State University, 31 Mar. 2006. Web. 15 Oct. 2010. [http://www.geology.sdsu.edu/how_volcanoes_work/Krakatau.html] {{Webarchive|url=https://web.archive.org/web/20141216203501/http://www.geology.sdsu.edu/how_volcanoes_work/Krakatau.html|date=2014-12-16}}.</ref>

A 2006 BBC documentary film, ''Ten Things You Didn't Know About Volcanoes'',<ref>{{IMDb title|qid=Q130302251|id=tt1027751|title=Ten Things You Didn't Know About Volcanoes (2006)}}</ref> demonstrated tests by a research team at [[Kiel University]], Germany, of pyroclastic flows moving over the water.<ref>[http://cat.inist.fr/?aModele=afficheN&cpsidt=14575991 Entrance of hot pyroclastic flows into the sea: experimental observations], [[INIST]].</ref> When the reconstructed pyroclastic flow (stream of mostly hot ash with varying densities) hit the water, two things happened: the heavier material fell into the water, precipitating out from the pyroclastic flow and into the liquid; the temperature of the ash caused the water to evaporate, propelling the pyroclastic flow (now only consisting of the lighter material) along on a bed of steam at an even faster pace than before.

During some phases of the Soufriere Hills volcano on Montserrat, pyroclastic flows were filmed about {{convert|1|km|nmi|frac=2|abbr=on}} offshore. These show the water boiling as the flow passes over it. The flows eventually built a delta, which covered about {{convert|1|km2|acre|sigfig=2|abbr=on}}. Another example was observed in 2019 at [[Stromboli]] when a pyroclastic flow traveled for several hundreds of meters above the sea.<ref>{{Cite web|first1=Sandro|last1=de Vita|first2=Mauro A.|last2=Di Vito|first3=Rosella|last3=Nave|date=2019-09-05|title=Quando un flusso piroclastico scorre sul mare: esempi a Stromboli e altri vulcani|url=https://ingvvulcani.com/2019/09/05/quando-un-flusso-piroclastico-scorre-sul-mare-esempi-a-stromboli-e-altri-vulcani/|access-date=2021-10-04|website=INGV vulcani|language=it-IT}}</ref>

A pyroclastic flow can interact with a body of water to form a large amount of mud, which can then continue to flow downhill as a [[lahar]]. This is one of several mechanisms that can create a lahar.{{citation needed|date=July 2020}}

===On other celestial bodies===
In 1963, NASA astronomer [[Winifred Cameron]] proposed that the lunar equivalent of terrestrial pyroclastic flows may have formed sinuous [[rille]]s on the [[Moon]]. In a lunar volcanic eruption, a pyroclastic cloud would follow local relief, resulting in an often sinuous track. The Moon's [[Schroter's Valley|Schröter's Valley]] offers one example.<ref>
{{cite journal | last1 = Cameron | first1 = W. S. | year = 1964 
| title = An Interpretation of Schröter's Valley and Other Lunar Sinuous Rills 
| journal = [[Journal of Geophysical Research]] | volume = 69 | issue = 12
| pages = 2423–2430 | doi = 10.1029/JZ069i012p02423 
| bibcode=1964JGR....69.2423C
}}
</ref>{{Primary source inline|date=July 2019}}
Some volcanoes on [[Mars]], such as [[Tyrrhenus Mons]] and [[Hadriacus Mons]], have produced layered deposits that appear to be more easily eroded than lava flows, suggesting that they were emplaced by pyroclastic flows.<ref>{{cite book |last1=Zimbelman |first1=James R. |last2=Garry |first2=William Brent |last3=Bleacher |first3=Jacob Elvin |last4=Crown |first4=David A. |editor1-last=Sigurdsson |editor1-first=Haraldur |editor2-last=Houghton |editor2-first=Bruce |editor3-last=McNutt |editor3-first=Steve |editor4-last=Rymer |editor4-first=Hazel |editor5-last=Stix |editor5-first=John |title=The Encyclopedia of Volcanoes |date=2015 |publisher=Zimbelman |location=Amsterdam |isbn=978-0-12-385938-9 |pages=717–728 |edition=Second |chapter-url=https://www.sciencedirect.com/science/article/pii/B9780123859389000419 |chapter=Volcanism on Mars}}</ref>