Editing Geyser (section)

== Geology ==
=== Form and function ===
[[File:Steamboat Geyser in Yellowstone.jpg|thumb|upright=1.1|alt=Water and steam erupting from rocky, barren ground, and fir trees in the background|[[Steamboat Geyser]] in [[Yellowstone National Park]]]]

Geysers are nonpermanent geological features. Geysers are generally associated with areas of recent [[magmatism]].<ref name=annrev>{{cite journal |url=https://www.annualreviews.org/content/journals/10.1146/annurev-earth-063016-015605 |journal=Annual Review of Earth and Planetary Sciences |volume=45 |year=2017 |title=The Fascinating and Complex Dynamics of Geyser Eruptions |first1=Shaul |last1=Hurwitz |first2=Michael |last2=Manga |issue=1 |pages=31–59 |doi=10.1146/annurev-earth-063016-015605 |bibcode=2017AREPS..45...31H}}</ref> As the water boils, the resulting pressure forces a superheated column of steam and water to the surface through the geyser's internal plumbing.<ref name=annrev/> The formation of geysers specifically requires the combination of three geologic conditions that are usually found in volcanic terrain: heat, water, and a subsurface hydraulic system with the right geometry.<ref name=annrev/>

The heat needed for geyser formation comes from [[magma]] that needs to be close to the surface of the Earth.<ref>{{Cite book |url=https://books.google.com/books?id=ljXMs4rkv3gC&q=heat+for+geyser+formation+comes+from+near+surface+magma&pg=PA127 |title=Quakes, Eruptions, and Other Geologic Cataclysms: Revealing the Earth's Hazards |last=Erickson |first=Jon |date=14 May 2014 |publisher=Infobase Publishing |isbn=9781438109695}}</ref> For the heated water to form a geyser, a plumbing system (made of [[fracture]]s, [[ground fissure|fissures]], porous spaces, and sometimes cavities) is required. This includes a reservoir to hold the water while it is being heated.<ref name=annrev/>

Geysers tend to be coated with [[geyserite]], or [[siliceous sinter]]. The water in geysers comes in contact with hot [[silica]]-containing rocks, such as [[rhyolite]]. The heated water dissolves the silica. As it gets closer to the surface, the water cools and the silica drops out of solution, leaving a deposit of [[amorphous]] [[opal]]. Gradually the opal anneals into [[quartz]], forming geyserite.  Geyserite often covers the microbial mats that grow in geysers. As the mats grow and the silica is deposited, the mats can form up to 50% of the volume of the geyserite.<ref>{{cite web |title=Geysers—what exactly are they made of? |work=Yellowstone Volcano Observatory |publisher=USGS |url=https://www.usgs.gov/news/geysers-what-exactly-are-they-made |date=23 March 2020}}</ref>

=== Eruptions ===
{{Multiple image
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|total_width=300
|width=150
|header=[[Strokkur|Strokkur geyser]] erupting <br/>(clockwise from top left)
|image1=geyser exploding 1 large.jpg
|image2=geyser exploding 2 large.jpg
|image3=geyser exploding 3 large.jpg
|image4=geyser exploding 4 large.jpg
|caption1=Steam rises from heated water
|caption2=Pulses of water swell upward
|caption3=Surface is broken
|caption4=Ejected water spouts upward and falls back down into the pipe
}}

Geyser activity, like all hot spring activity, is caused by surface water gradually seeping down through the ground until it meets [[geothermal energy|geothermally heated]] rock.<ref name=usgs>{{cite web |url=https://www.nps.gov/subjects/geology/hot-springs.htm |title=Hot Springs/Geothermal Features |publisher=USGS |date=10 February 2020}}</ref> In non-eruptive hot springs, the heated water then rises back toward the surface by [[convection]] through porous and fractured rocks, while in geysers, the water instead is explosively forced upwards by the high [[steam]] pressure created when water boils below.<ref name=usgs/> Geysers also differ from non-eruptive hot springs in their subterranean structure: geysers have constrictions in their plumbing that create pressure build-up.<ref>{{cite web |url=https://www.nps.gov/yell/learn/nature/hydrothermal-features.htm |title=Hydrothermal features |work=Yellowstone |publisher=National Park Service |access-date=27 October 2024}}</ref>

As the geyser fills, the water at the top of the column cools off, but because of the narrowness of the channel, [[Convection|convective cooling]] of the water in the reservoir is impossible. The cooler water above presses down on the hotter water beneath, not unlike the lid of a [[pressure cooker]], allowing the water in the reservoir to become [[superheating|superheated]], i.e. to remain liquid at temperatures well above the standard-pressure boiling point.<ref name=howGeyersWork>{{cite web |archive-url=https://web.archive.org/web/20160316083033/http://www.nps.gov/yell/learn/nature/geysers.htm |archive-date=16 March 2016 |url=http://www.nps.gov/yell/learn/nature/geysers.htm |title=Geysers |work=Yellowstone |publisher=National Park Service}}</ref>

Ultimately, the temperatures near the bottom of the geyser rise to a point where boiling begins, forcing steam bubbles to rise to the top of the column. As they burst through the geyser's vent, some water overflows or splashes out, reducing the weight of the column and thus the pressure on the water below. With this release of pressure, the superheated water flashes into steam, boiling violently throughout the column. The resulting froth of expanding steam and hot water then sprays out of the geyser vent.<ref name=annrev/><ref>{{cite journal |last=Lewin |first=Sarah |title=Instant Egghead: How do geysers erupt over and over? |journal=[[Scientific American]] |year=2015 |volume=312 |issue=5 |page=27 |doi=10.1038/scientificamerican0515-27 |pmid=26336706 |url=http://www.scientificamerican.com/article/instant-egghead-how-do-geysers-erupt-over-and-over |access-date=17 May 2015|url-access=subscription }}</ref>

Eventually the water remaining in the geyser cools back to below the boiling point and the eruption ends; heated groundwater begins seeping back into the reservoir, and the whole cycle begins again. The duration of eruptions and the time between successive eruptions vary greatly from geyser to geyser; [[Strokkur]] in Iceland erupts for a few seconds every few minutes,<ref>{{cite journal |last1=Eibl |first1=EPS |last2=Hainzl |first2=S |last3=Vesely |first3=NIK |last4=Walter |first4=TR |last5=Jousset |first5=P |last6=Hersir |first6=GP |last7=Dahm |first7=T |doi=10.1029/2019GL085266 |title=Eruption Interval Monitoring at Strokkur Geyser, Iceland |journal=Geophysical Research Letters |volume=47 |issue=1 |year=2019}}</ref> while [[Grand Geyser]] in the United States erupts for up to 10&nbsp;minutes every 8–12&nbsp;hours.<ref>{{Cite web |title=Grand Geyser |archive-url=https://web.archive.org/web/20061027103300/https://www.nps.gov/archive/yell/tours/oldfaithful/grandg.htm |archive-date=27 October 2006 |url=https://www.nps.gov/archive/yell/tours/oldfaithful/grandg.htm |work=Yellowstone |publisher=National Park Service}}</ref>

=== General categorization ===

There are two types of geysers: ''fountain geysers'' which erupt from pools of water, typically in a series of intense, even violent, bursts; and ''cone geysers'' which erupt from cones or mounds of [[siliceous sinter]] (including [[geyserite]]), usually in steady jets that last anywhere from a few seconds to several minutes. [[Old Faithful Geyser|Old Faithful]], perhaps the best-known geyser at Yellowstone National Park, is an example of a cone geyser. [[Grand Geyser]], the tallest predictable geyser on Earth (although [[Geysir]] in Iceland is taller, it is not predictable), also at Yellowstone National Park, is an example of a fountain geyser.<ref>{{cite book |last=Bryan |first=T. Scott |title=The Geysers of Yellowstone |edition=Fifth |location=United States |publisher=University Press of Colorado |year=2018}}</ref>

{{multiple image
 |direction = horizontal
 |align     = left
 |width1    = 202
 |width2    = 180
 |image1    = Fountain geyser.jpg
 |image2    = Old Faithful Geyser Yellowstone National Park.jpg
 |alt1      = Geyser erupts up and blows sideways from a pool.
 |alt2      = High geyser of water erupts out of the sparsely vegetated earth.
 |footer    = [[Fountain Geyser]] erupting from the pool (left) and [[Old Faithful geyser]] (cone geyser having mound of siliceous sinter) in [[Yellowstone National Park]] erupts approximately every 91 minutes (right).
}}

There are many volcanic areas in the world that have [[hot spring]]s, [[mud pot]]s and [[fumarole]]s, but very few have erupting geysers. The main reason for their rarity is that multiple intense transient forces must occur simultaneously for a geyser to exist. For example, even when other necessary conditions exist, if the rock structure is loose, eruptions will erode the channels and rapidly destroy any nascent geysers.<ref>{{Cite thesis |last=Brown |first=Sabrina |year=2019 |title=Diatom-inferred records of paleolimnological variability and continental hydrothermal activity in Yellowstone National Park, USA |url=https://digitalcommons.unl.edu/geoscidiss/122 |type=PhD dissertation |publisher=University of Nebraska–Lincoln}}</ref>

Geysers are fragile, and if conditions change, they may go dormant or extinct. Many have been destroyed simply by people throwing debris into them, while others have ceased to erupt due to dewatering by [[geothermal power]] plants. However, the Geysir in Iceland has had periods of activity and dormancy. During its long dormant periods, eruptions were sometimes artificially induced—often on special occasions—by the addition of [[surfactant]] soaps to the water.<ref name="Pasvanoglu_etal_2000">{{cite journal |title=Geochemical Study of the Geysir Geothermal Field in Haukadalur, S. Iceland |first1=S. |last1=Pasvanoglu |first2=H. |last2=Kristmannsdóttir |first3=S. |last3=Björnsson |first4=H. |last4=Torfason |journal=Proceedings World Geothermal Congress 2000 |year=2000}}</ref>
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