View source for Geyser

=== Eruptions ===
{{Multiple image
|perrow = 2
|total_width=300
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|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|article-number=e2019GL085266 |doi-access=free }}</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>