Editing Stratovolcano

{{Short description|Type of conical volcano composed of layers of lava and tephra}}
{{Use dmy dates|date=October 2024}}

[[File:Rainier20200906.jpg|thumb|upright=1.35|[[Mount Rainier]], a {{convert|14411|ft|m|0|order=flip|abbr=on}} stratovolcano, the highest point in the US state of Washington]]
[[File:Broken Top rock layers.jpg|thumb|upright=1.35|Exposed internal structure of alternating layers of [[lava]] and [[pyroclastic rock]] in the [[Erosion|eroded]] [[Broken Top]] stratovolcano in [[Oregon]]]]

A '''stratovolcano''', also known as a '''composite volcano''', is a typically [[Volcanic cone|conical]] [[volcano]] built up by many alternating layers ([[Stratum|strata]]) of hardened [[lava]] and [[tephra]].<ref>{{USGS|url=http://pubs.usgs.gov/gip/volc/types.html|title=Principal Types of Volcanoes|access-date=19 January 2009}}</ref> Unlike [[shield volcano]]es, stratovolcanoes are characterized by a steep profile with a summit crater and explosive eruptions.<ref>{{Cite web|title=Types of volcano|url=https://www.bgs.ac.uk/discovering-geology/earth-hazards/volcanoes/how-volcanoes-form/#:~:text=Stratovolcanoes%20are%20more%20likely%20to,rocks%20in%20different%20tectonic%20settings.|access-date=24 October 2024|publisher=British Geological Survey}}</ref> Some have collapsed summit craters called [[caldera]]s.<ref>{{Cite web|title=Volcanoes: Principal Types of Volcanoes|url=https://pubs.usgs.gov/gip/volc/types.html|access-date=24 October 2024|publisher=United States Geological Survey}}</ref> The [[lava]] flowing from stratovolcanoes typically cools and solidifies before spreading far, due to high [[viscosity]]. The [[magma]] forming this lava is often [[felsic]], having high to intermediate levels of [[silica]] (as in [[rhyolite]], [[dacite]], or [[andesite]]), with lesser amounts of less viscous [[mafic]] [[magma]].<ref>{{Cite book|url=https://www.springer.com/gp/book/9783642258923|title=Teide Volcano: Geology and Eruptions of a Highly Differentiated Oceanic Stratovolcano|date=2013|publisher=Springer-Verlag|isbn=978-3-642-25892-3|editor-last=Carracedo|editor-first=Juan Carlos|series=Active Volcanoes of the World|location=Berlin Heidelberg|editor-last2=Troll|editor-first2=Valentin R.}}</ref> Extensive [[felsic]] lava flows are uncommon, but can travel as far as 8&nbsp;km (5&nbsp;mi).<ref>{{Cite web|title=Lava flows destroy everything in their path {{!}} U.S. Geological Survey|url=https://www.usgs.gov/programs/VHP/lava-flows-destroy-everything-their-path|access-date=24 October 2024|publisher=United States Geological Survey}}</ref>

The term ''composite volcano'' is used because strata are usually mixed and uneven instead of neat layers.<ref>{{Cite web|title=Composite Volcanoes (Stratovolcanoes) (U.S. National Park Service)|url=https://www.nps.gov/articles/000/composite-volcanoes.htm|access-date=24 October 2024|publisher=National Park Service}}</ref> They are among the most common types of volcanoes;<ref name=":0">{{Cite web|date=28 September 2024|title=Stratovolcano {{!}} Shape, Examples, & Facts {{!}} Britannica|url=https://www.britannica.com/science/stratovolcano|access-date=24 October 2024|website=Encyclopædia Britannica}}</ref> more than 700 stratovolcanoes have erupted lava during the [[Holocene Epoch]] (the last 11,700 years),<ref name="GVP_Holocene_Composite">{{cite web|url=https://volcano.si.edu/volcanolist_holocene.cfm|title=Holocene Volcano List|publisher=[[Smithsonian Institution]] [[Global Volcanism Program]]|work=Volcanoes of the World (version 5.2.4)|date=21 Oct 2024|access-date=3 November 2024}}</ref> and many older, now extinct, stratovolcanoes erupted lava as far back as [[Archean]] times.<ref name="GVP_Pleistocene_Composite">{{cite web|url=https://volcano.si.edu/volcanolist_pleistocene.cfm|title=Pleistocene Volcano List|publisher=[[Smithsonian Institution]] [[Global Volcanism Program]]|work=Volcanoes of the World (version 5.2.4)|date=21 Oct 2024|access-date=3 November 2024}}</ref><ref>{{cite journal|url=https://publications.gc.ca/Collection-R/GSC-CGC/M42E/581/GSC_B581.pdf|title=Back River Volcanic Complex: An Archean Stratovolcano, Nunavut-Northwest Territories|last=Lambert|first=M.B.|journal=Geological Survey of Canada Bulletin 581|year=2005}}</ref> Stratovolcanoes are typically found in [[Subduction|subduction zones]] but they also occur in other geological settings. Two examples of stratovolcanoes famous for catastrophic eruptions are [[Krakatoa]] in [[Indonesia]] (which erupted in [[1883 eruption of Krakatoa|1883]] claiming 36,000 lives)<ref>{{Cite web|date=25 August 2017|title=On This Day: Historic Krakatau Eruption of 1883|url=https://www.ncei.noaa.gov/news/day-historic-krakatau-eruption-1883|access-date=24 October 2024|publisher=National Centers for Environmental Information (NCEI)}}</ref> and Mount [[Vesuvius]] in [[Italy]] (which erupted in [[Eruption of Mount Vesuvius in 79|79]] A.D killing an estimated 2,000 people).<ref>{{Cite web|title=Vesuvius Erupts|url=https://www.amnh.org/exhibitions/permanent/planet-earth/why-are-there-ocean-basins-continents-and-mountains/explosive-volcanism/vesuvius-erupts|publisher=American Museum of Natural History}}</ref> In modern times, [[Mount St. Helens]] (1980) in [[Washington (state)|Washington State]], US, and [[Mount Pinatubo]] (1991) in the [[Philippines]] have erupted catastrophically, but with fewer deaths.<ref name=":0" />

The existence of stratovolcanoes on other bodies of the [[Solar System]] has not been conclusively demonstrated.<ref>{{cite book|last1=Barlow|first1=Nadine|title=Mars : an introduction to its interior, surface and atmosphere|date=2008|publisher=Cambridge University Press|location=Cambridge, UK|isbn=9780521852265}}</ref> [[Zephyria Tholus]] is one of two mountains in the [[Aeolis quadrangle|Aeolis region]] of Mars that have been proposed as possible stratovolcanoes.<ref name=mars>{{cite journal|last1=Stewart|first1=Emily M.|last2=Head|first2=James W.|title=Ancient Martian volcanoes in the Aeolis region: New evidence from MOLA data|journal=Journal of Geophysical Research|date=1 August 2001|volume=106|issue=E8|pages=17505|doi=10.1029/2000JE001322|bibcode=2001JGR...10617505S|doi-access=free}}</ref>

==Distribution==
[[File:Subduction-en.svg|thumb|upright=1.5|Cross-section of subduction zone and associated stratovolcanoes]]

Stratovolcanoes are common at [[subduction]] zones, forming chains and clusters along [[Plate tectonics|plate tectonic]] boundaries where an [[oceanic crust]] plate is drawn under a [[continental crust]] plate (continental arc volcanism, e.g. [[Cascade Range]], [[Andes]], [[Campanian volcanic arc|Campania]]) or another [[oceanic crust]] plate ([[island arc]] volcanism, e.g. [[Japan]], [[Philippines]], [[Aleutian Islands]]).<ref>{{Cite web|title=How volcanoes form|url=https://www.bgs.ac.uk/discovering-geology/earth-hazards/volcanoes/how-volcanoes-form-2/|access-date=25 October 2024|publisher=British Geological Survey|language=en-GB}}</ref>

Stratovolcanoes also occur in some other geological settings, for example as a result of [[intraplate volcanism]] on oceanic islands far from plate boundaries. Examples are [[Teide]] in the [[Canary Islands]],<ref name="Cas_etal_2022">{{cite journal|title=Tenerife, a complex end member of basaltic oceanic island volcanoes, with explosive polygenetic phonolitic calderas, and phonolitic-basaltic stratovolcanoes|last1=Cas|first1=R.A.F.|last2=Wolff|first2=J.A.|last3=Martí|first3=J.|last4=Olin|first4=P.H.|last5=Edgar|first5=C.J.|last6=Pittari|first6=A.|last7=Simmons|first7=J.M.|journal=Earth-Science Reviews|year=2022|volume=230|article-number=103990|doi=10.1016/j.earscirev.2022.103990|bibcode=2022ESRv..23003990C |hdl=10261/267257|hdl-access=free}}</ref> and [[Pico do Fogo]] in [[Cape Verde]].<ref name="Carvalho_etal_2022">{{cite journal|title=3D-ambient noise surface wave tomography of Fogo volcano, Cape Verde|last1=Carvalho|first1=J.|last2=Silveira|first2=G.|last3=Dumont|first3=S.|last4=Ramalho|first4=R.|journal=Journal of Volcanology and Geothermal Research|year=2022|volume=432|article-number=107702|doi=10.1016/j.jvolgeores.2022.107702|bibcode=2022JVGR..43207702C }}</ref> 
Stratovolcanoes have formed in continental [[rift]]s. Examples in the [[East African Rift]] are [[Ol Doinyo Lengai]] in Tanzania,<ref name="OlDoinyoGVP">{{cite web|url=https://volcano.si.edu/volcano.cfm?vn=222120|title=Ol Doinyo Lengai|publisher=[[Smithsonian Institution]]|work=[[Global Volcanism Program]], Volcanoes of the World, version 5.2.4|date=21 October 2024|access-date=5 December 2024}}</ref> and [[Longonot]] in Kenya.<ref name="LongonotGVP">{{cite web|url=https://volcano.si.edu/volcano.cfm?vn=222100|title=Longonot|publisher=[[Smithsonian Institution]]|work=[[Global Volcanism Program]], Volcanoes of the World, version 5.2.4|date=21 October 2024|access-date=5 December 2024}}</ref>

==Formation==
[[Subduction|Subduction zone]] volcanoes form when [[hydrous]] [[mineral]]s are pulled down into the mantle on the slab. These hydrous minerals, such as [[chlorite]] and [[Serpentine subgroup|serpentine]], release their water into the [[Earth's mantle|mantle]] which decreases its [[melting point]] by 60 to 100&nbsp;°C. The release of water from [[hydrate]]d minerals is termed "[[dewatering]]", and occurs at specific pressures and temperatures for each mineral, as the plate descends to greater depths.<ref>{{Citation|last1=Schmidt|first1=A.|last2=Rüpke|first2=L. H.|last3=Morgan|first3=J. P.|last4=Hort|first4=M.|date=1 December 2001|title=How Large a Feedback Effect Does Slab Dewatering Have on Itself ?|journal=AGU Fall Meeting Abstracts |url=https://ui.adsabs.harvard.edu/abs/2001AGUFM.T41C0871S/abstract|volume=2001|pages=T41C–0871|bibcode=2001AGUFM.T41C0871S }}</ref> This allows the [[Earth's mantle|mantle]] to partially melt and generate [[magma]]. This is called [[flux melting]]. The magma then rises through the [[Crust (geology)|crust]], incorporating silica-rich crustal rock, leading to a final [[intermediate composition]]. When the magma nears the top surface, it pools in a [[magma chamber]] within the crust below the stratovolcano.<ref>{{Cite web|title=4 Igneous Processes and Volcanoes – An Introduction to Geology|url=https://opengeology.org/textbook/4-igneous-processes-and-volcanoes/|access-date=25 October 2024|language=en}}</ref>

The processes that trigger the final eruption remain a question for further research. Possible mechanisms include:<ref name=":3">{{cite journal|last1=Cañón-Tapia|first1=Edgardo|title=Volcanic eruption triggers: A hierarchical classification|journal=Earth-Science Reviews|date=February 2014|volume=129|pages=100–119|doi=10.1016/j.earscirev.2013.11.011|bibcode=2014ESRv..129..100C}}</ref>

* [[Igneous differentiation|Magma differentiation]], in which the lightest, most silica-rich magma and volatiles such as water, [[halogen]]s, and [[sulfur dioxide]] accumulate in the uppermost part of the magma chamber. This can dramatically increase pressures.<ref>{{Cite web|last=Nelson|first=Stephan|date=14 September 2015|title=Volcanoes, Magma, and Volcanic Eruptions|url=https://www2.tulane.edu/~sanelson/Natural_Disasters/volcan&magma.htm|publisher=Tulane University}}</ref>
* [[Fractional crystallization (geology)|Fractional crystallization]] of the magma. When [[anhydrous]] [[mineral]]s such as [[feldspar]] crystallize out of the magma, this concentrates volatiles in the remaining liquid, which can lead to a second boiling that causes a [[Phase (matter)|gas phase]] (carbon dioxide or water) to separate from the liquid magma and raise magma chamber pressures.<ref>{{cite journal|last1=Wech|first1=Aaron G.|last2=Thelen|first2=Weston A.|last3=Thomas|first3=Amanda M.|title=Deep long-period earthquakes generated by second boiling beneath Mauna Kea volcano|journal=Science|date=15 May 2020|volume=368|issue=6492|pages=775–779|doi=10.1126/science.aba4798|pmid=32409477|bibcode=2020Sci...368..775W|s2cid=218648557}}</ref><ref>{{Cite journal|last1=Garcia-Arias|first1=Marcos|last2=Stevens|first2=Gary|date=15 April 2017|title=Phase equilibrium modelling of granite magma petrogenesis: B. An evaluation of the magma compositions that result from fractional crystallization|url=https://www.sciencedirect.com/science/article/abs/pii/S002449371630319X|journal=Lithos|series=Eighth Hutton Symposium on Granites and Related Rocks|volume=277|pages=109–130|doi=10.1016/j.lithos.2016.09.027|bibcode=2017Litho.277..109G |issn=0024-4937}}</ref>
* Injection of fresh magma into the magma chamber, which mixes and heats the cooler magma already present. This could force volatiles out of solution and lower the density of the cooler magma, both of which increase pressure. There is considerable evidence for magma mixing just before many eruptions, including magnesium-rich [[olivine]] crystals in freshly erupted silicic [[lava]] that show no reaction rim. This is possible only if the [[lava]] erupted immediately after mixing since olivine rapidly reacts with silicic magma to form a rim of [[pyroxene]].<ref>{{Cite journal|last1=Scandone|first1=Roberto|last2=Cashman|first2=Katharine V.|last3=Malone|first3=Stephen D.|date=30 January 2007|title=Magma supply, magma ascent and the style of volcanic eruptions|url=https://www.sciencedirect.com/science/article/abs/pii/S0012821X06008181|journal=Earth and Planetary Science Letters|volume=253|issue=3|pages=513–529|doi=10.1016/j.epsl.2006.11.016|bibcode=2007E&PSL.253..513S |issn=0012-821X}}</ref>
* Progressive melting of the surrounding [[country rock (geology)|country rock]].<ref name=":3" />

These internal triggers may be modified by external triggers such as [[sector collapse]], [[earthquake]]s, or [[Phreatomagmatic eruption|interactions with groundwater]]. Some of these triggers operate only under limited conditions. For example, sector collapse (where part of the flank of a volcano collapses in a massive [[landslide]]) can only trigger the eruption of a very shallow magma chamber. Magma differentiation and [[thermal expansion]] also are ineffective as triggers for eruptions from deep magma chambers.<ref name=":3" />

==Hazards==
{{Main|Volcanic hazard}}
[[File:Etna from 2900m.jpg|thumb|Mount Etna on the island of [[Sicily]], in southern Italy]]
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| footer            = [[Mount Fuji]] on [[Honshu]] (top) and [[Mount Unzen]] on [[Kyushu]] (bottom), two of [[Japan]]'s stratovolcanoes
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In [[recorded history]], explosive eruptions at [[Subduction|subduction zone]] ([[Convergent boundary|convergent-boundary]]) volcanoes have posed the greatest hazard to civilizations.<ref name="dynearth">{{USGS|title=Plate tectonics and people|last1=Kious|first1=W. Jacquelyne|last2=Tilling|first2=Robert I.|url=http://pubs.usgs.gov/gip/dynamic/tectonics.html}}</ref> [[Subduction|Subduction-zone]] stratovolcanoes, such as [[Mount St. Helens]], [[Mount Etna]] and [[Mount Pinatubo]], typically erupt with explosive force because the [[magma]] is too [[Viscosity|viscous]] to allow easy escape of [[volcanic gas]]es.<ref>{{Cite web|title=Types of volcano|url=https://www.bgs.ac.uk/discovering-geology/earth-hazards/volcanoes/how-volcanoes-form/#:~:text=NASA%20Earth%20Observatory.-,Stratovolcano,a%20volcano%20with%20steep%20sides.|access-date=24 October 2024|publisher=British Geological Survey}}</ref> As a consequence, the tremendous internal pressures of the trapped volcanic gases remain and intermingle in the pasty [[magma]].  Following the breaching of the [[Volcanic vent|vent]] and the opening of the crater, the [[magma]] degasses explosively. The magma and gases blast out with high speed and full force.<ref name="dynearth"/>

Since 1600 [[Common Era|CE]], nearly 300,000 people have been killed by [[volcanic eruptions]]. Most deaths were caused by [[pyroclastic flow]]s and [[lahar]]s, deadly hazards that often accompany explosive eruptions of [[Subduction|subduction-zone]] stratovolcanoes.<ref name="dynearth" /> Pyroclastic flows are swift, avalanche-like, ground-sweeping, incandescent mixtures of hot volcanic debris, fine [[Volcanic ash|ash]], fragmented [[lava]], and superheated gases that can travel at speeds over {{convert|150|km/h|sigfig=1|abbr=on}}.<ref name="dynearth" /> Around 30,000 people were killed by pyroclastic flows during the [[1902 eruption of Mount Pelée]] on the island of [[Martinique]] in the [[Caribbean]].<ref name="dynearth"/> During March and April 1982, [[El Chichón]] in the State of [[Chiapas]] in southeastern [[Mexico]], erupted 3 times, causing the worst volcanic disaster in that country's history and killied more than 2,000 people in pyroclastic flows.<ref name="dynearth"/>

Two [[Decade Volcanoes]] that erupted in 1991 provide examples of stratovolcano hazards. On 15 June, Mount Pinatubo erupted and caused an [[Volcanic ash|ash cloud]] to shoot 40&nbsp;km (25&nbsp;mi) into the air. It produced large [[pyroclastic surge]]s and [[lahar]] floods that caused a lot of damage to the surrounding area.<ref name="dynearth" /> Mount Pinatubo, located in [[Central Luzon]] just 90&nbsp;km (56&nbsp;mi) west-northwest of [[Manila]], had been dormant for six centuries before the 1991 eruption. This eruption was one of the 2nd largest in the 20th century.<ref name=":1">{{Cite web|title=The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines, Fact Sheet 113-97|url=https://pubs.usgs.gov/fs/1997/fs113-97/|access-date=24 October 2024|publisher=United States Geological Survey}}</ref> It produced a large [[volcanic ash]] cloud that affected global temperatures, lowering them in areas as much as .5&nbsp;°C.<ref name=":1" /> The [[volcanic ash]] cloud consisted of 22 million tons of [[Sulfur dioxide|SO<sub>2</sub>]] which combined with water droplets to create [[sulfuric acid]].<ref name="dynearth" /> In 1991 Japan's [[Mount Unzen]] also erupted, after 200 years of inactivity. It's located on the island of [[Kyushu]] about 40&nbsp;km (25&nbsp;mi) east of [[Nagasaki]].<ref name="dynearth" /> Beginning in June, a newly formed lava dome repeatedly collapsed. This generated a pyroclastic flow that flowed down the mountain's slopes at speeds as high as 200&nbsp;km/h (120&nbsp;mph).<ref name="dynearth" /> The 1991 eruption of Mount Unzen was one of the worst volcanic disasters in Japan's history, once killing more than 15,000 people in 1792.<ref>{{Cite web|title=Mount Unzen eruption of 1792 {{!}} Volcanic Disaster, Deceit & Death {{!}} Britannica|url=https://www.britannica.com/event/Mount-Unzen-eruption-of-1792|access-date=24 October 2024|website=Encyclopædia Britannica}}</ref>

The [[eruption of Mount Vesuvius in 79 AD]] is the most famous example of a hazardous stratovolcano eruption. It completely smothered the nearby ancient cities of [[Pompeii]] and [[Herculaneum]] with thick deposits of [[pyroclastic surge]]s and [[pumice]] ranging from 6–7 meters deep. Pompeii had 10,000–20,000 inhabitants at the time of eruption.<ref>{{Cite web|date=25 September 2024|title=Pompeii {{!}} History, Volcano, Map, Population, Ruins, & Facts {{!}} Britannica|url=https://www.britannica.com/place/Pompeii#ref5859|access-date=25 September 2024|website=Encyclopædia Britannica}}</ref> [[Mount Vesuvius]] is recognized as one of the most dangerous of the world's volcanoes, due to its capacity for [[Plinian eruption|powerful explosive eruptions]] coupled with the high population density of the surrounding [[Metropolitan City of Naples|Metropolitan Naples]] area (totaling about 3.6 million inhabitants).<ref>{{Cite journal|last=Rolandi|first=G.|date=January 2010|title=Volcanic hazard at Vesuvius: An analysis for the revision of the current emergency plan|url=https://linkinghub.elsevier.com/retrieve/pii/S0377027309003254|journal=Journal of Volcanology and Geothermal Research|volume=189|issue=3–4|pages=347–362|doi=10.1016/j.jvolgeores.2009.08.007|bibcode=2010JVGR..189..347R }}</ref>

===Ash===
{{main|Volcanic ash}}
[[File:Ashfall from Pinatubo, 1991.jpg|thumb|Snow-like blanket of [[Mount Pinatubo]]'s ashfall deposits in a parking lot on [[Clark Air Base]] (15 June 1991)]]

In addition to potentially affecting the climate, [[volcanic ash]] clouds from [[explosive eruption]]s pose a serious hazard to [[aviation]].<ref name="dynearth"/> [[Volcanic ash]] clouds consist of silt- or sand-sized pieces of rock, mineral, [[volcanic glass]]. Volcanic ash grains are jagged, abrasive, and don't dissolve in water.<ref name=":22">{{Cite web|title=Ash Fall—A "Hard Rain" of Abrasive Particles {{!}} USGS Volcano Fact Sheet|url=https://pubs.usgs.gov/fs/fs027-00/|access-date=16 October 2024|publisher=United States Geological Survey}}</ref> For example, during the 1982 eruption of [[Galunggung]] in [[Java]], [[British Airways Flight 9]] flew into the ash cloud, causing it to sustain temporary engine failure and structural damage.<ref>{{Cite web|title=Global Volcanism Program {{!}} Report on Galunggung (Indonesia) – June 1982|url=https://volcano.si.edu/showreport.cfm?doi=10.5479/si.GVP.SEAN198206-263140|access-date=24 October 2024|publisher=Global Volcanism Program|doi=10.5479/si.gvp.sean198206-263140}}</ref> Although no crashes have happened due to ash, more than 60, mostly [[commercial aircraft]], have been damaged. Some of these incidents resulted in emergency landings.<ref name=":05">{{Cite web|title=Plate tectonics and people [This Dynamic Earth, USGS]|url=https://pubs.usgs.gov/gip/dynamic/tectonics.html|access-date=25 September 2024|publisher=United States Geological Survey}}</ref><ref name="dynearth"/> [[Volcanic ash|Ashfalls]] are a threat to health when inhaled and are also a threat to property. A square yard of a 4-inch thick volcanic ash layer can weigh 120–200 pounds and can get twice as heavy when wet. Wet ash also poses a risk to electronics due to its [[Electrical conductor|conductive]] nature.<ref name=":22"/> Dense clouds of hot volcanic ash can be expelled due to the collapse of an [[Eruption column|eruptive column]], or laterally due to the partial collapse of a [[volcanic edifice]] or [[lava dome]] during [[explosive eruption]]s. These clouds are known as [[pyroclastic surge]]s and in addition to volcanic ash, they contain hot [[lava]], [[pumice]], [[Volcanic rock|rock]], and volcanic gas. Pyroclastic surges flow at speeds over 50&nbsp;mph and are at temperatures between 200&nbsp;°C – 700&nbsp;°C. These surges can cause major damage to property and people in their path.<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=16 October 2024|publisher=United States Geological Survey}}</ref>

===Lava===
{{main|Lava}}
[[File:Mayon 0052.jpg|right|thumb|[[Mayon|Mayon Volcano]] in [[Philippines]] extruding lava flows during its eruption on 29 December 2009]]

[[Lava|Lava flows]] from stratovolcanoes are generally not a significant threat to humans or animals because the highly [[Viscosity|viscous]] [[lava]] moves slowly enough for everyone to evacuate. Most deaths attributed to lava are due to related causes such as [[explosion]]s and [[asphyxia]]tion from [[toxic gas]].<ref name=":12">{{Cite web|title=Lava flows destroy everything in their path|url=https://www.usgs.gov/programs/VHP/lava-flows-destroy-everything-their-path|access-date=16 October 2024|publisher=United States Geological Survey}}</ref> [[Lava|Lava flows]] can bury homes and farms in thick [[volcanic rock]] which greatly reduces property value.<ref name=":12" /> However, not all stratovolcanoes erupt viscous and sticky lava. [[Nyiragongo]], near [[Lake Kivu]] in [[central Africa]], is very dangerous because its [[magma]] has an unusually low [[Silicate|silica content]], making it much less viscous than other stratovolcanoes. Low [[viscosity]] lava can generate massive [[lava fountain]]s, while lava of thicker viscosity can solidify within the vent, creating a [[volcanic plug]]. Volcanic plugs can trap [[volcanic gas]] and create pressure in the magma chamber, resulting in violent eruptions.<ref>{{Cite web|title=Eruption styles|url=https://www.bgs.ac.uk/discovering-geology/earth-hazards/volcanoes/eruption-styles/|access-date=24 October 2024|publisher=British Geological Survey}}</ref> Lava is typically between 700 and 1,200&nbsp;°C (1,300–2,200&nbsp;°F).<ref>{{Cite web|date=23 September 2024|title=Lava {{!}} Types, Composition, Temperature, & Facts {{!}} Britannica|url=https://www.britannica.com/science/lava-volcanic-ejecta|access-date=24 October 2024|website=Encyclopædia Britannica}}</ref>

===Volcanic bombs===
{{main|Volcanic bomb}}

[[Volcanic bomb]]s are masses of unconsolidated rock and lava that are ejected during an eruption. Volcanic bombs are classified as larger than 64mm (2.5 inches). Anything from 2 to 64mm is classified as [[lapilli]].<ref name=":03">{{Cite web|title=Volcanic Bombs: Overview|url=https://www.sandatlas.org/volcanic-bomb/|access-date=24 October 2024|website=sandatlas.org}}</ref> When erupted, volcanic bombs are still molten and partially cool and solidify on their descent. They can form ribbon or oval shapes that can also flatten on impact with the ground.<ref>{{Cite web|title=Bomb {{!}} Explosive Eruption, Pyroclastic Flow, Ash Cloud {{!}} Britannica|url=https://www.britannica.com/science/bomb-volcanic-ejecta|access-date=24 October 2024|website=Encyclopædia Britannica}}</ref> Volcanic bombs are associated with [[Strombolian eruption|Strombolian]] and [[Vulcanian eruption|Vulcanian]] eruptions and [[basaltic lava]]. Ejection velocities ranging from 200 to 400&nbsp;m/s have been recorded causing volcanic bombs to be destructive.<ref name=":03" />

===Lahar===
{{main|Lahar}}

[[Lahar]]s (from a [[Javanese language|Javanese]] term for volcanic mudflows) are a mixture of volcanic debris and water. Lahars can result from heavy rainfall during or before the eruption or interaction with ice and snow. Meltwater mixes with volcanic debris causing a fast moving mudflow. Lahars are typically about 60% sediment and 40% water.<ref name=":04">{{Cite web|title=Volcanic hazards|url=https://www.bgs.ac.uk/discovering-geology/earth-hazards/volcanoes/volcanic-hazards/|access-date=24 October 2024|publisher=British Geological Survey}}</ref> Depending on the abundance of volcanic debris the lahar can be fluid or thick like concrete.<ref name=":13">{{Cite web|title=Plate tectonics and people [This Dynamic Earth, USGS]|url=https://pubs.usgs.gov/gip/dynamic/tectonics.html|access-date=24 October 2024|publisher=United States Geological Survey}}</ref> [[Lahar]]s have the strength and speed to flatten structures and cause great bodily harm, gaining speeds up to dozens of kilometers per hour.<ref name=":04" /> In the [[Armero tragedy|1985 eruption]] of [[Nevado del Ruiz]] in [[Colombia]], [[Pyroclastic surge]]s melted snow and ice atop the 5,321&nbsp;m (17,457&nbsp;ft) high Andean volcano. The ensuing lahar killed 25,000 people and flooded the city of [[Armero]] and nearby settlements.<ref name=":13" />

=== Volcanic gas ===
{{Main|Volcanic gas}}
As a volcano forms, several different [[Volcanic gas|gases]] mix with [[magma]] in the volcanic chamber. During an eruption the gases are then released into the [[atmosphere]] which can lead to toxic human exposure. The most abundant of these [[Volcanic gas|gases]] is [[Water|H<sub>2</sub>O]] ([[water]]) followed by [[Carbon dioxide|CO<sub>2</sub>]] ([[carbon dioxide]]), [[Sulfur dioxide|SO<sub>2</sub>]] ([[sulfur dioxide]]), [[Hydrogen sulfide|H<sub>2</sub>S]] ([[hydrogen sulfide]]), and [[Hydrogen fluoride|HF]] ([[hydrogen fluoride]]).<ref name=":04"/> If at concentrations of more than 3% in the air, when breathed in [[Carbon dioxide|CO<sub>2</sub>]] can cause dizziness and difficulty breathing. At more than 15% concentration [[Carbon dioxide|CO<sub>2</sub>]] causes death. [[Carbon dioxide|CO<sub>2</sub>]] can settle into depressions in the land, leading to deadly, odorless pockets of gas.<ref name=":06">{{Cite web|title=Volcanic gases can be harmful to health, vegetation and infrastructure {{!}} U.S. Geological Survey|url=https://www.usgs.gov/programs/VHP/volcanic-gases-can-be-harmful-health-vegetation-and-infrastructure|access-date=24 October 2024|publisher=United States Geological Survey}}</ref> [[Sulfur dioxide|SO<sub>2</sub>]] classified as a respiratory, skin, and eye irritant if come into contact with. It is known for its pungent egg smell and role in ozone depletion and has the potential to cause acid rain downwind of an eruption.<ref name=":06" /> [[Hydrogen sulfide|H<sub>2</sub>S]] has an even stronger odor than [[Sulfur dioxide|SO<sub>2</sub>]] as well as being even more toxic. Exposure for less than an hour at concentrations of over 500 ppm causes death.<ref name=":06" /> [[Hydrogen fluoride|HF]] and similar species can coat [[ash]] particles and once deposited can poison soil and water.<ref name=":06" /> Gases are also emitted during volcanic degassing, which is a passive release of [[gas]] during periods of dormancy.<ref name=":06" />

==Eruptions that affected global climate==
[[File:Ausbruch des Pinatubo 1991.jpg|thumb|Mount Pinatubo's 1991 eruption ash cloud seen from Clark Airbase. 12 June 1991]]
As per the above examples, while eruptions like [[Mount Unzen]] have caused deaths and local damage, the impact of the June 1991 eruption of [[Mount Pinatubo]] was seen globally.<ref name=":05"/> The eruptive columns reached heights of 40&nbsp;km and dumped 17 megatons of SO<sub>2</sub> into the lower [[stratosphere]].<ref name=":14">{{Cite web|title=Self|url=https://pubs.usgs.gov/pinatubo/self/|access-date=25 October 2024|publisher=United States Geological Survey}}</ref> The [[aerosol]]s that formed from the [[sulfur dioxide]] (SO<sub>2</sub>), [[carbon dioxide]] (CO<sub>2</sub>), and other [[Volcanic gas|gases]] dispersed around the world. The [[Sulfur dioxide|SO<sub>2</sub>]] in this cloud combined with water (both of volcanic and atmospheric origin) and formed [[sulfuric acid]], blocking a portion of the sunlight from reaching the [[troposphere]].<ref name=":05" /> This caused the global temperature to decrease by about 0.4&nbsp;°C (0.72&nbsp;°F) from 1992 to 1993. These [[aerosol]]s caused the [[ozone layer]] to reach the lowest concentrations recorded at that time.<ref name=":14" /> An eruption the size of Mount Pinatubo affected the weather for a few years; with warmer winters and cooler summers observed.<ref name=":14" />

A similar phenomenon occurred in the April 1815, the eruption of [[Mount Tambora]] on [[Sumbawa]] island in [[Indonesia]]. This eruption is recognized as the most powerful eruption in recorded history.<ref name=":05" /> Its eruption cloud lowered global temperatures as much as 0.4 to 0.7&nbsp;°C.<ref name=":2">{{Cite web|date=24 October 2024|title=This Day In History: Mount Tambora Explosively Erupts in 1815|url=https://www.nesdis.noaa.gov/news/day-history-mount-tambora-explosively-erupts-1815|access-date=25 October 2024|website=National Environmental Satellite, Data, and Information Service|language=en}}</ref> In the year following the eruption, most of the Northern Hemisphere experienced cooler temperatures during the summer. In the [[Northern Hemisphere|northern hemisphere]], 1816 was known as the "[[Year Without a Summer]]". The eruption caused crop failures, food shortages, and floods that killed over 100,000 people across Europe, Asia, and North America.<ref name=":2" />

==List==
{{main|List of stratovolcanoes}}

==See also==
* {{annotated link|Cinder cone}}
* {{annotated link|Mountain formation}}
* {{annotated link|Orogeny}}
* {{annotated link|Pyroclastic shield}}

==References==
{{reflist}}

{{Volcanoes}}

{{Authority control}}

[[Category:Stratovolcanoes| ]]
[[Category:Volcanic landforms]]