Editing Rhyolite (section)

==Geology==
Due to their high content of silica and low [[iron]] and [[magnesium]] contents, rhyolitic [[magmas]] form highly viscous [[lava]]s.<ref name="philpotts-ague-2009"/>{{rp|23–26}} As a result, many eruptions of rhyolite are highly explosive, and rhyolite occurs more frequently as [[pyroclastic rock]] than as [[lava flow]]s.<ref name="fisher-schmincke-1984">{{cite book |last1=Fisher |first1=Richard V. |last2=Schmincke |first2=H.-U. |title=Pyroclastic rocks |date=1984 |publisher=Springer-Verlag |location=Berlin |isbn=3540127569}}</ref>{{rp|22}} Rhyolitic ash flow [[tuff]]s are the only volcanic product with volumes rivaling those of [[flood basalt]]s.<ref name="philpotts-ague-2009"/>{{rp|77}} Rhyolites also occur as [[breccia]]s or in [[lava dome]]s, [[volcanic plug]]s, and [[dike (geology)|dikes]].<ref>{{cite journal |last1=Hanson |first1=Richard E. |last2=Schweickert |first2=Richard A. |title=Chilling and Brecciation of a Devonian Rhyolite Sill Intruded into Wet Sediments, Northern Sierra Nevada, California |journal=The Journal of Geology |date=1 November 1982 |volume=90 |issue=6 |pages=717–724 |doi=10.1086/628726|bibcode=1982JG.....90..717H |s2cid=128948336 }}</ref><ref>{{cite journal |last1=Spell |first1=Terry L. |last2=Kyle |first2=Philip R. |title=Petrogenesis of Valle Grande Member rhyolites, Valles Caldera, New Mexico: Implications for evolution of the Jemez Mountains Mgmatic System |journal=Journal of Geophysical Research: Solid Earth |date=1989 |volume=94 |issue=B8 |pages=10379–10396 |doi=10.1029/JB094iB08p10379|bibcode=1989JGR....9410379S }}</ref><ref name="philpotts-ague-2009"/>{{rp|71–72}} Rhyolitic lavas erupt at a relatively low temperature of {{convert|800|to|1000|°C|abbr=on}}, significantly cooler than basaltic lavas, which typically erupt at temperatures of {{convert|1100|to|1200|°C|abbr=on}}.<ref name="philpotts-ague-2009"/>{{rp|20}}

Rhyolites that cool too quickly to grow [[crystals]] form a natural glass or vitrophyre, also called [[obsidian]].<ref>{{cite book |last1=Raymond |first1=Loren A. |title=Petrology : the study of igneous, sedimentary, metamorphic rocks |date=1997 |publisher=McGraw-Hill Companies, Inc |location=Dubuque, IA |isbn=0697413403 |page=27 |edition=Complete customized version}}</ref> Slower cooling forms microscopic crystals in the lava and results in textures such as flow [[foliation (geology)|foliations]], [[spherulite|spherulitic]], [[Nodule (geology)|nodular]], and [[lithophysa]]l structures. Some rhyolite is highly [[Vesicular texture|vesicular]] [[pumice]].<ref name="blatt-tracy-1996-55-74"/>

[[Peralkaline rock|Peralkaline]] rhyolites (rhyolites unusually rich in alkali metals) include [[comendite]] and [[pantellerite]].<ref>{{cite journal |last1=Mbowou|first1=Gbambie Isaac Bertrand|last2=Lagmet|first2=Claudial|last3=Nomade|first3=Sébastien|last4=Ngounoun|first4=Ismaïla|last5=Déruelle|first5=Bernard|last6=Ohnenstetter|first6=Daniel|title=Petrology of the Late Cretaceous peralkaline rhyolites (pantellerite and comendite) from Lake Chad, Central Africa|journal=[[Journal of Geosciences]]|year=2012|volume=57|page=127|doi=10.3190/jgeosci.118|issn=1802-6222|doi-access=free}}</ref> Peralkalinity has significant effects on [[lava morphology|lava flow morphology]] and [[mineralogy]], such that peralkaline rhyolites can be 10–30 times more fluid than typical [[calc-alkaline]] rhyolites. As a result of their increased fluidity, they are able to form small-scale flow folds, [[lava tube]]s and thin dikes. Peralkaline rhyolites erupt at relatively high temperatures of more than {{convert|1200|°C|abbr=on}}. They comprise [[bimodal volcanism|bimodal]] [[shield volcano]]es at [[hotspot (geology)|hotspot]]s and [[rift]]s (e.g. [[Rainbow Range (Chilcotin Plateau)|Rainbow Range]], [[Ilgachuz Range]] and [[Level Mountain]] in [[British Columbia]], Canada).<ref>{{cite book|last=Wood|first=Charles A.|author2=Kienle, Jürgen |pages=123. 131, 132, 133 |url=https://books.google.com/books?id=eyDRib-FJh4C|title=Volcanoes of North America: United States and Canada|year=1990|publisher=[[Cambridge University Press]]|location=[[Cambridge]], England|isbn=0-521-43811-X}}</ref>

Eruptions of rhyolite lava are relatively rare compared to eruptions of less felsic lavas. Only four eruptions of rhyolite have been recorded since the start of the 20th century: at the [[St. Andrew Strait]] volcano in [[Papua New Guinea]] and [[Novarupta]] volcano in [[Alaska]] as well as at [[Chaitén]] and [[Cordón Caulle]] volcanoes in southern [[Chile]].<ref name="Wilson_2011">{{cite conference | url=https://ui.adsabs.harvard.edu/abs/2011AGUFM.V42A..01W/abstract | title=Insights Into the Workings of Rhyolitic Explosive Eruptions and Their Magmatic Sources | publisher=[[American Geophysical Union]] | access-date=27 October 2020 | last=Wilson | first=C.J. | journal=AGU Fall Meeting Abstracts | year=2011 | volume=2011 | pages=V42A–01 | bibcode=2011AGUFM.V42A..01W | conference=American Geophysical Union Fall Meeting 2011 | id=abstract id. V42A-01}}</ref><ref name="Magnall_etal_2017">{{cite journal | title=Emplacing a Cooling-Limited Rhyolite Lava Flow: Similarities with Basaltic Lava Flows | first1=N. | last1=Magnall | first2=M.R. | last2=James | first3=H. | last3=Tuffen | first4=C. | last4=Vye-Brown | journal=Frontiers in Earth Science | year=2017 | volume=5 | page=44 | doi=10.3389/feart.2017.00044| bibcode=2017FrEaS...5...44M | s2cid=12887930 | doi-access=free }}</ref> The eruption of Novarupta in 1912 was the largest volcanic eruption of the 20th century,<ref name="Fierstein1998">{{cite journal |author=Fierstein, Judy |author-link=Judy Fierstein |last2=Hildreth |first2=Wes |author-link2=Wes Hildreth |author3=Hendley, James W. II |author4=Stauffer, Peter H. |year=1998 |title=Can Another Great Volcanic Eruption Happen in Alaska? |url=http://pubs.usgs.gov/fs/fs075-98/ |journal=U.S. Geological Survey Fact Sheet 075-98 |version=Version 1.0 |publisher=[[United States Geological Survey]] |access-date=September 10, 2008}}</ref> and began with explosive volcanism that later transitioned to effusive volcanism and the formation of a rhyolite dome in the vent.<ref name="nguyen-etal-2014">{{cite journal |last1=Nguyen |first1=Chinh T. |last2=Gonnermann |first2=Helge M. |last3=Houghton |first3=Bruce F. |title=Explosive to effusive transition during the largest volcanic eruption of the 20th century (Novarupta 1912, Alaska) |journal=Geology |date=August 2014 |volume=42 |issue=8 |pages=703–706 |doi=10.1130/G35593.1|bibcode=2014Geo....42..703N |s2cid=129328343 |url=https://pdfs.semanticscholar.org/94f8/c9017db99bb31c3d11edd42de0d5e04be424.pdf |archive-url=https://web.archive.org/web/20200219110722/https://pdfs.semanticscholar.org/94f8/c9017db99bb31c3d11edd42de0d5e04be424.pdf |url-status=dead |archive-date=2020-02-19 }}</ref>