Editing Yellowstone National Park (section)

=== Volcanism ===
[[File:Columnar basalt closeup near Tower Fall in Yellowstone.JPG|thumb|[[Basalt#Columnar basalt|Columnar basalt]] near [[Tower Fall]]; large floods of basalt and other lava types preceded mega-eruptions of superheated ash and pumice.]]
[[File:Caldera rim.jpg|thumb|Caldera rim on the horizon south of Yellowstone Lake]]
Yellowstone is at the northeastern end of the [[Snake River Plain]], a great bow-shaped arc through the mountains that extends roughly {{convert|400|mi|km|-1}} from the park to the Idaho-Oregon border.

The volcanism of Yellowstone is believed to be linked to the somewhat older volcanism of the Snake River Plain. Yellowstone is thus the active part of a [[hotspot (geology)|hotspot]] that the [[North American Plate]] has moved over in a southwest direction over time.<ref name="snake">{{cite web |url=http://tapestry.usgs.gov/features/34snakeriver.html |title=The Snake River Plain |publisher=U.S. Geological Survey |date=March 12, 2001 |access-date=March 12, 2007 |url-status=dead |archive-url=https://web.archive.org/web/20130412140625/http://tapestry.usgs.gov/features/34snakeriver.html |archive-date=April 12, 2013 }}</ref> The origin of this hotspot volcanism is disputed.<ref name=James2011/> One theory holds that a [[mantle plume]] has caused the [[Yellowstone hotspot]] to migrate, while another theory explains migrating hotspot volcanism as the result of the fragmentation and dynamics of the [[subduction|subducted]] [[Farallon Plate]] in Earth's interior.<ref name=James2011>{{cite journal |last1=James |first1=David |last2=Fouch |first2=Matthew |last3=Carlson |first3=Richard W. |last4=Roth |first4=Jeffrey |year=2011 |title=Slab Fragmentation, Edge Flow and the Origin of the Yellowstone Hotspot Track |journal=Earth and Planetary Science Letters |volume=311 |issue=1–2 |pages=124–135 |doi=10.1016/j.epsl.2011.09.007 |bibcode=2011E&PSL.311..124J }}</ref><ref name=zhou2018>{{cite journal |last1=Zhou |first1=Ying |year=2018 |title=Anomalous mantle transition zone beneath the Yellowstone hotspot track |journal=Nature Geoscience |volume=11 |issue=6 |pages=449–453 |doi=10.1038/s41561-018-0126-4 |bibcode=2018NatGe..11..449Z |s2cid=134251160 }}</ref>

The [[Yellowstone Caldera]] is the largest volcanic system in North America, and worldwide it is only rivaled by the [[Lake Toba|Lake Toba Caldera]] on [[Sumatra]]. It has been termed a "[[supervolcano]]" because the caldera was formed by exceptionally large explosive eruptions. The [[magma chamber]] that lies under Yellowstone is estimated to be a single connected chamber, about {{convert|37|mi|km}} long, {{convert|18|mi|km}} wide, and {{convert|3|to|7|mi|km}} deep.<ref name=Oskin>{{cite news |last=Oskin |first=Becky |title=Yellowstone's Volcano Bigger Than Thought |url=http://www.livescience.com/28821-yellowstone-supervolcano-bigger-plume.html |access-date=August 11, 2013 |newspaper=[[LiveScience]] |date=April 17, 2013 |url-status=live |archive-url=https://web.archive.org/web/20130702230721/http://www.livescience.com/28821-yellowstone-supervolcano-bigger-plume.html |archive-date=July 2, 2013 }}</ref> The current [[caldera]] was created by a cataclysmic eruption that occurred 640,000&nbsp;years ago, which released more than {{convert|240|mi3|km3|abbr=on}} of ash, rock and [[pyroclast]]ic materials.<ref name="640ka">{{cite web |url=http://pubs.usgs.gov/pp/pp729g |title=The Quaternary and Pliocene Yellowstone Plateau Volcanic Field of Wyoming, Idaho, and Montana |publisher=U.S. Geological Survey |date=August 27, 2001 |access-date=May 11, 2013 |url-status=live |archive-url=https://web.archive.org/web/20130512144946/http://pubs.usgs.gov/pp/pp729g/ |archive-date=May 12, 2013}}/</ref> This eruption was more than 1,000 times larger than the [[1980 eruption of Mount St. Helens]].<ref name="volcanic">{{cite web |url=http://pubs.usgs.gov/fs/fs100-03/ |title=Tracking Changes in Yellowstone's Restless Volcanic System |publisher=U.S. Geological Survey |date=January 19, 2006 |access-date=March 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070206103530/http://pubs.usgs.gov/fs/fs100-03/ |archive-date=February 6, 2007 }}</ref> It produced a caldera nearly {{cvt|5/8|mi}} deep and {{convert|45|by|28|mi|km}} in area and deposited the [[Lava Creek Tuff]], a [[welded tuff]] [[geologic formation]]. The most violent known eruption, which occurred 2.1&nbsp;million years ago, ejected {{convert|588|mi3|km3|abbr=on}} of volcanic material and created the rock formation known as the [[Huckleberry Ridge Tuff]] and the [[Island Park Caldera]].<ref name="volcanic history">{{cite web |url=http://volcanoes.usgs.gov/yvo/history.html |title=Volcanic History of the Yellowstone Plateau Volcanic Field |website=Yellowstone Volcano Observatory |publisher=U.S. Geological Survey |date=February 2, 2007 |access-date=March 12, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070318093739/http://volcanoes.usgs.gov/yvo/history.html |archive-date=March 18, 2007 }}</ref> A smaller eruption ejected {{convert|67|mi3|km3|abbr=on}} of material 1.3&nbsp;million years ago, forming the [[Henry's Fork Caldera]] and depositing the [[Mesa Falls Tuff]].<ref name="volcanic"/>

Each of the three climactic eruptions released vast amounts of ash that blanketed much of central North America, falling many hundreds of miles away. The amount of ash and gases released into the atmosphere probably caused significant impacts on world weather patterns and led to the [[extinction]] of some species, primarily in North America.<ref name="sciamerican">{{cite journal |last=Bindeman |first=Ilya N. |title=The Secrets of Supervolcanoes |journal=Scientific American |url=http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0006E0BF-BB43-146C-BB4383414B7F0000 |archive-url=https://web.archive.org/web/20071016204122/http://www.sciam.com/article.cfm?chanID=sa006&colID=1&articleID=0006E0BF-BB43-146C-BB4383414B7F0000 |archive-date=October 16, 2007 |date=June 2006 |volume=294 |issue=6 |pages=36–43 |doi=10.1038/scientificamerican0606-36 |pmid=16711358 |bibcode=2006SciAm.294f..36B |access-date=August 24, 2011 |url-access=subscription }}</ref>
[[File:Aerial image of Grand Prismatic Spring (view from the south).jpg|left|thumb|Boardwalks allow visitors to safely approach the thermal features, such as [[Grand Prismatic Spring]]]]

A subsequent caldera-forming eruption occurred about 160,000 years ago. It formed the relatively small caldera that contains the [[Yellowstone Lake|West Thumb]] of Yellowstone Lake. Since the last supereruption, a series of smaller eruptive cycles between 640,000 and 70,000&nbsp;years ago, has nearly filled in the Yellowstone Caldera with 80 different eruptions of [[rhyolite|rhyolitic]] lavas such as those that can be seen at [[Obsidian Cliff]]s and [[basalt]]ic lavas which can be viewed at [[Sheepeater Cliff]]. Lava strata are most easily seen at the Grand Canyon of the Yellowstone, where the Yellowstone River continues to carve into the ancient lava flows. The canyon is a classic [[V-shaped valley]], indicative of river-type erosion rather than erosion caused by [[glacier|glaciation]].<ref name="volcanic history"/>

Each eruption is part of an eruptive cycle that climaxes with the partial collapse of the roof of the volcano's partially emptied magma chamber. This creates a collapsed depression, called a caldera, and releases vast amounts of volcanic material, usually through fissures that ring the caldera. The time between the last three cataclysmic eruptions in the Yellowstone area has ranged from 600,000 to 800,000&nbsp;years; however, the small number of such climactic eruptions cannot be used to make an accurate prediction for future volcanic events.<ref name="time">{{cite web |url=http://volcanoes.usgs.gov/yvo/faqsfactivity.html#eruptagain |title=Questions About Future Volcanic Activity |website=Yellowstone Volcano Observatory |publisher=U.S. Geological Survey |date=February 2, 2007 |access-date=April 8, 2007 |url-status=live |archive-url=https://web.archive.org/web/20120118011434/http://volcanoes.usgs.gov/yvo/faqsfactivity.html#eruptagain |archive-date=January 18, 2012 }}</ref>