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Answer: A spring occurs when an aquifer fills to the point where groundwater spills out into a lake or river or onto the land surface. It forms where the side of a hill, a valley bottom, a lakebed, or other excavation intersects groundwater at or below the local water table.

Sizes

Springs range in size from intermittent seeps, which flow only after much rain, to huge pools flowing hundreds of millions of gallons daily. Large springs are rare but small ones are found in many different places.

How rock shapes springs

Springs may be formed in any sort of rock. In Missouri, the largest springs are formed in limestone and dolomite, two types of rock found in the karst topography of the Ozarks. Both fracture relatively easily.

• Weak carbonic acid, formed by rainwater percolating through organic matter in the soil, enters these fractures and dissolves bedrock.
• When it reaches a horizontal crack or a layer of non-dissolving rock such as sandstone or shale, it begins to cut sideways.
• As the process continues, the water hollows out more rock, eventually admitting an airspace, at which point the spring stream can be considered a cave.

Springs under the sea

Springs are not limited to the Earth's surface. Scientists have discovered hot springs at depths of up to 2.5 kilometers in the oceans, generally along mid-ocean rifts. The hot water, over 300 degrees Celsius, is rich in minerals and sulfur, which results in a unique ecosystem.

In the water cycle

Groundwater can return to the surface through natural discharge into rivers, the ocean, and from springs.

Claims

• id: C1 claim: Springs may be formed in any sort of rock. source: S1 evidence: "Springs may be formed in any sort of rock."
• id: C2 claim: Large springs are rare but small ones are found in many places. source: S1 evidence: "Large springs are rare but small ones are found in many different places."
• id: C3 claim: Below ground, liquid water is stored as groundwater in aquifers. source: S2 evidence: "Deeper below ground, liquid water is stored as groundwater in aquifers."

Sources

• [S1] Springs and the Water Cycle. USGS. https://www.usgs.gov/special-topics/water-science-school/science/springs-and-water-cycle . License: US government work, public domain. Accessed 2026-11-04.
• [S2] Water cycle. USGS. https://www.usgs.gov/special-topics/water-science-school/science/water-cycle . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_9rhxah9b,
  author = {{iinventedlight}},
  title = {{Springs: where groundwater reaches the surface}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/springs/},
  note = {Permanent ID iil:note:9rhxah9b. License: CC-BY-4.0.},
}

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