Editing Caldera (section)

===Explosive caldera eruptions===
{{Further|Explosive eruption}}
Explosive caldera eruptions are produced by a magma chamber whose [[magma]] is rich in [[silica]]. Silica-rich magma has a high [[viscosity]], and therefore does not flow easily like [[basalt]].<ref name="philpotts-ague-2009" />{{rp|23–26}} The magma typically also contains a large amount of dissolved gases, up to 7 [[wt%]] for the most silica-rich magmas.<ref>{{cite book |last1=Schmincke |first1=Hans-Ulrich |title=Volcanism |date=2003 |publisher=Springer |location=Berlin |isbn=9783540436508 |pages=42–43}}</ref> When the magma approaches the surface of the Earth, the drop in [[confining pressure]] causes the trapped gases to rapidly bubble out of the magma, fragmenting the magma to produce a mixture of [[volcanic ash]] and other [[tephra]] with the very hot gases.{{sfn|Schmincke|2003|pp=155–157}}

The mixture of ash and volcanic gases initially rises into the atmosphere as an [[eruption column]]. However, as the volume of erupted material increases, the eruption column is unable to [[Entrainment (hydrodynamics)|entrain]] enough air to remain buoyant, and the eruption column collapses into a tephra fountain that falls back to the surface to form [[pyroclastic flows]].{{sfn|Schmincke|2003|p=157}} Eruptions of this type can spread ash over vast areas, so that ash flow [[tuff]]s emplaced by silicic caldera eruptions are the only volcanic product with volumes rivaling those of [[flood basalt]]s.<ref name="philpotts-ague-2009" />{{rp|77}} For example, when [[Yellowstone Caldera]] last erupted some 650,000 years ago, it released about 1,000&nbsp;km<sup>3</sup> of material (as measured in dense rock equivalent (DRE)), covering a substantial part of [[North America]] in up to two metres of debris.<ref name="USGSFS3024">{{cite web|first1=Jacob B. |last1=Lowenstern |first2=Robert L. |last2=Christiansen |first3=Robert B. |last3=Smith |first4=Lisa A. |last4=Morgan |first5=Henry |last5=Heasler |title=Steam Explosions, Earthquakes, and Volcanic Eruptions—What's in Yellowstone's Future? – U.S. Geological Survey Fact Sheet 2005–3024 |publisher=[[United States Geological Survey]] |date=May 10, 2005|url=http://pubs.usgs.gov/fs/2005/3024/}}</ref>

Eruptions forming even larger calderas are known, such as the [[La Garita Caldera]] in the [[San Juan Mountains]] of [[Colorado]], where the {{convert|5000|km3}} [[Fish Canyon Tuff]] was blasted out in eruptions about 27.8&nbsp;million years ago.<ref name=livescience>{{cite web | url=http://www.livescience.com/11113-biggest-volcanic-eruption.html|title=What's the Biggest Volcanic Eruption Ever?| publisher=livescience.com | date=10 November 2010 | access-date=2014-02-01}}</ref><ref>{{cite journal |last1=Best |first1=Myron G. |last2=Christiansen |first2=Eric H. |last3=Deino |first3=Alan L. |last4=Gromme |first4=Sherman |last5=Hart |first5=Garret L. |last6=Tingey |first6=David G. |title=The 36–18 Ma Indian Peak–Caliente ignimbrite field and calderas, southeastern Great Basin, USA: Multicyclic super-eruptions |journal=Geosphere |date=August 2013 |volume=9 |issue=4 |pages=864–950 |doi=10.1130/GES00902.1 |bibcode=2013Geosp...9..864B |doi-access=free }}</ref>

{{anchor|Outflow sheet}}
The caldera produced by such eruptions is typically filled in with tuff, [[rhyolite]], and other [[igneous rock]]s.<ref name="troll-etal-2000">{{Cite journal|last1=Troll|first1=Valentin R.|last2=Emeleus|first2=C. Henry|last3=Donaldson|first3=Colin H.|date=2000-11-01|title=Caldera formation in the Rum Central Igneous Complex, Scotland|url=https://doi.org/10.1007/s004450000099|journal=Bulletin of Volcanology|language=en|volume=62|issue=4|pages=301–317|doi=10.1007/s004450000099|bibcode=2000BVol...62..301T|s2cid=128985944|issn=1432-0819|url-access=subscription}}</ref> The caldera is surrounded by an '''outflow sheet''' of ash flow tuff (also called an '''ash flow sheet''').<ref>{{cite journal |last1=Best |first1=Myron G. |last2=Christiansen |first2=Eric H. |last3=Deino |first3=Alan L. |last4=Grommé |first4=C. Sherman |last5=Tingey |first5=David G. |title=Correlation and emplacement of a large, zoned, discontinuously exposed ash flow sheet: The 40 Ar/ 39 Ar chronology, paleomagnetism, and petrology of the Pahranagat Formation, Nevada |journal=Journal of Geophysical Research: Solid Earth |date=10 December 1995 |volume=100 |issue=B12 |pages=24593–24609 |doi=10.1029/95JB01690|bibcode=1995JGR...10024593B }}</ref><ref>{{cite journal |last1=Cook |first1=Geoffrey W. |last2=Wolff |first2=John A. |last3=Self |first3=Stephen |title=Estimating the eruptive volume of a large pyroclastic body: the Otowi Member of the Bandelier Tuff, Valles caldera, New Mexico |journal=Bulletin of Volcanology |date=February 2016 |volume=78 |issue=2 |pages=10 |doi=10.1007/s00445-016-1000-0|bibcode=2016BVol...78...10C |s2cid=130061015 }}</ref>

If magma continues to be injected into the collapsed magma chamber, the center of the caldera may be uplifted in the form of a ''[[resurgent dome]]'' such as is seen at the [[Valles Caldera]], [[Lake Toba]], the San Juan volcanic field,<ref name="smith-bailey-1968">{{cite journal |last1=Smith |first1=Robert L. |last2=Bailey |first2=Roy A. |title=Resurgent Cauldrons |journal=Geological Society of America Memoirs |date=1968 |volume=116 |pages=613–662 |doi=10.1130/MEM116-p613}}</ref> [[Galán|Cerro Galán]],<ref>{{cite journal |last1=Grocke |first1=Stephanie B. |last2=Andrews |first2=Benjamin J. |last3=de Silva |first3=Shanaka L. |title=Experimental and petrological constraints on long-term magma dynamics and post-climactic eruptions at the Cerro Galán caldera system, NW Argentina |journal=Journal of Volcanology and Geothermal Research |date=November 2017 |volume=347 |pages=296–311 |doi=10.1016/j.jvolgeores.2017.09.021|bibcode=2017JVGR..347..296G |doi-access=free }}</ref> [[Yellowstone Caldera|Yellowstone]],<ref>{{cite journal |last1=Tizzani |first1=P. |last2=Battaglia |first2=M. |last3=Castaldo |first3=R. |last4=Pepe |first4=A. |last5=Zeni |first5=G. |last6=Lanari |first6=R. |title=Magma and fluid migration at Yellowstone Caldera in the last three decades inferred from InSAR, leveling, and gravity measurements |journal=Journal of Geophysical Research: Solid Earth |date=April 2015 |volume=120 |issue=4 |pages=2627–2647 |doi=10.1002/2014JB011502|bibcode=2015JGRB..120.2627T |doi-access=free |hdl=11573/779666 |hdl-access=free }}</ref> and many other calderas.<ref name="smith-bailey-1968"/>

Because a silicic caldera may erupt hundreds or even thousands of cubic kilometers of material in a single event, it can cause catastrophic environmental effects. Even small caldera-forming eruptions, such as [[Krakatoa]] in 1883<ref>{{cite journal |last1=Schaller |first1=N |last2=Griesser |first2=T |last3=Fischer |first3=A |last4=Stickler |first4=A. and |last5=Brönnimann |first5=S. |year=2009 |title=Climate effects of the 1883 Krakatoa eruption: Historical and present perspectives |journal=VJSCHR. Natf. Ges. Zürich |volume=154 |pages=31–40 |url=https://www.researchgate.net/publication/255700466 |access-date=29 December 2020}}</ref> or [[Mount Pinatubo]] in 1991,<ref>{{cite journal |last1=Robock |first1=A. |title=PINATUBO ERUPTION: The Climatic Aftermath |journal=Science |date=15 February 2002 |volume=295 |issue=5558 |pages=1242–1244 |doi=10.1126/science.1069903|pmid=11847326 |s2cid=140578928 }}</ref> may result in significant local destruction and a noticeable [[Volcanic winter|drop in temperature]] around the world. Large calderas may have even greater effects. The ecological effects of the eruption of a large caldera can be seen in the record of the [[Lake Toba]] eruption in [[Indonesia]].

At some points in [[geological time]], rhyolitic calderas have appeared in distinct clusters. The remnants of such clusters may be found in places such as the [[Eocene]] [[Rùm#Geology|Rum]] Complex of Scotland,<ref name="troll-etal-2000"/> the San Juan Mountains of Colorado (formed during the [[Oligocene]], [[Miocene]], and [[Pliocene]] epochs) or the [[Saint Francois Mountain Range]] of [[Missouri]] (erupted during the [[Proterozoic]] eon).<ref>{{cite book |last1=Kisvarsanyi |first1=Eva B. |title=Geology of the Precambrian St. Francois Terrane, Southeastern Missouri |date=1981 |publisher=Missouri Department of Natural Resources, Division of Geology and Land Survey |oclc=256041399 }}{{page needed|date=November 2019}}</ref>

====Valles====
[[File:Valle Caldera, New Mexico.jpg|thumb|Valle Caldera, New Mexico]]
{{Main|Valles Caldera}}
For their 1968 paper<ref name="smith-bailey-1968"/> that first introduced the concept of a resurgent caldera to geology,<ref name="cole-etal-2005"/> R.L. Smith and R.A. Bailey chose the Valles caldera as their model. Although the Valles caldera is not unusually large, it is relatively young (1.25 million years old) and unusually well preserved,<ref>{{cite journal |last1=Goff |first1=Fraser |last2=Gardner |first2=Jamie N. |last3=Reneau |first3=Steven L. |last4=Kelley |first4=Shari A. |last5=Kempter |first5=Kirt A. |last6=Lawrence |first6=John R. |title=Geologic map of the Valles caldera, Jemez Mountains, New Mexico |journal=New Mexico Bureau of Geology and Mineral Resources Map Series |date=2011 |volume=79 |bibcode=2011AGUFM.V13C2606G |url=https://geoinfo.nmt.edu/publications/maps/geologic/gm/79/  |access-date=18 May 2020}}</ref> and it remains one of the best studied examples of a resurgent caldera.<ref name="cole-etal-2005"/> The ash flow tuffs of the Valles caldera, such as the [[Bandelier Tuff]], were among the first to be thoroughly characterized.<ref>{{cite journal |last1=Ross |first1=Clarence S. |last2=Smith |first2=Robert L. |title=Ash-flow tuffs: Their origin, geologic relations, and identification |journal=U.S. Geological Survey Professional Paper |series=Professional Paper |date=1961 |volume=366 |page=7 |doi=10.3133/pp366|doi-access=free |bibcode=1961usgs.rept....7R |hdl=2027/ucbk.ark:/28722/h26b1t |hdl-access=free }}</ref>

====Toba====
{{Main|Lake Toba|Toba catastrophe theory}}

About 74,000 years ago, this Indonesian volcano released about {{convert|2800|km3}} [[dense-rock equivalent]] of ejecta. This was the largest known eruption during the ongoing [[Quaternary]] period (the last 2.6&nbsp;million years) and the largest known explosive eruption during the last 25&nbsp;million years. In the late 1990s, [[anthropologist]] Stanley Ambrose<ref>{{cite web | url=http://www.anthro.illinois.edu/people/ambrose | title=Stanley Ambrose page | publisher=University of Illinois at Urbana-Champaign | access-date=20 March 2014}}</ref> proposed that a [[volcanic winter]] induced by this eruption reduced the human population to about 2,000–20,000 individuals, resulting in a [[population bottleneck]]. More recently, [[Lynn Jorde]] and [[Henry Harpending]] proposed that the human species was reduced to approximately 5,000–10,000 people.<ref>[http://www.bbc.co.uk/science/horizon/1999/supervolcanoes_script.shtml Supervolcanoes], [[BBC2]], 3 February 2000</ref> There is no direct evidence, however, that either theory is correct, and there is no evidence for any other animal decline or extinction, even in environmentally sensitive species.<ref>{{cite journal |last1=Gathorne-Hardy |first1=F.J |last2=Harcourt-Smith |first2=W.E.H |title=The super-eruption of Toba, did it cause a human bottleneck? |journal=Journal of Human Evolution |date=September 2003 |volume=45 |issue=3 |pages=227–230 |doi=10.1016/s0047-2484(03)00105-2 |pmid=14580592 |bibcode=2003JHumE..45..227G }}</ref> There is evidence that human habitation continued in [[India]] after the eruption.<ref>{{cite journal |last1=Petraglia |first1=M. |last2=Korisettar |first2=R. |last3=Boivin |first3=N. |last4=Clarkson |first4=C. |last5=Ditchfield |first5=P. |last6=Jones |first6=S. |last7=Koshy |first7=J. |last8=Lahr |first8=M. M. |last9=Oppenheimer |first9=C. |last10=Pyle |first10=D. |last11=Roberts |first11=R. |last12=Schwenninger |first12=J.-L. |last13=Arnold |first13=L. |last14=White |first14=K. |title=Middle Paleolithic Assemblages from the Indian Subcontinent Before and After the Toba Super-Eruption |journal=Science |date=6 July 2007 |volume=317 |issue=5834 |pages=114–116 |doi=10.1126/science.1141564 |pmid=17615356 |bibcode=2007Sci...317..114P |s2cid=20380351 }}</ref>

[[File:La Cumbre - ISS.JPG|thumb|right|Satellite photograph of the summit caldera on [[Fernandina Island]] in the [[Galápagos Islands|Galápagos]] [[archipelago]]]]
[[File:Nemrut Caldera aerial.jpg|thumb|right|Oblique aerial photo of [[Nemrut (volcano)|Nemrut Caldera]], Van Lake, Eastern Turkey]]