Salt Questions · Science, chemistry & environment
How do salt mines form underground?
Short answer
Most underground salt formed when ancient seas or salt lakes evaporated, leaving thick layers of salt called evaporites. Over millions of years these layers were buried by sediment and preserved. Under pressure, salt can also flow upward into huge domes. Mines dig into these beds, many of them hundreds of millions of years old.
How a salt deposit forms
- 1Ancient sea or lake is cut off
- 2Water evaporates; salt crystallises
- 3Layers are buried by sediment
- 4Millions of years later: mined as rock salt
Step 1: evaporation
When an arm of the sea or a lake is cut off in a hot, dry climate, water evaporates faster than it is replaced. Minerals crystallise in order: carbonates and gypsum first, then halite (rock salt), then rarer potassium and magnesium salts.
Step 2: burial
Repeated flooding and drying can build salt layers hundreds of metres thick. Mud and sand later bury them, protecting the salt from dissolving.
Step 3: domes and folds
Salt is less dense than surrounding rock and flows slowly under pressure, rising into salt domes and pillars, common along the U.S. Gulf Coast.
Examples
The salt mined at Goderich, Ontario, and Hutchinson, Kansas, was deposited in ancient seas; the Kansas salt is about 275 million years old.
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Cite this page
For school projects and reports. Teachers often prefer the original sources too: see the list below.
The Salt Almanac. (2026, November 8). How do salt mines form underground. https://saltalmanac.com/answers/how-do-salt-mines-form-underground
“How do salt mines form underground.” The Salt Almanac, 8 Nov. 2026, saltalmanac.com/answers/how-do-salt-mines-form-underground. Accessed [today's date].
“How do salt mines form underground.” The Salt Almanac. Last modified November 8, 2026. https://saltalmanac.com/answers/how-do-salt-mines-form-underground.
Original sources
- Wikipedia. Evaporite. https://en.wikipedia.org/wiki/Evaporite
- Wikipedia. Halite. https://en.wikipedia.org/wiki/Halite
- Wikipedia. Salt dome. https://en.wikipedia.org/wiki/Salt_dome