Solutional cave

Hydrogen sulfide dissolution in Lechuguilla Cave, New Mexico

A solutional cave is a cave usually formed in the soluble rock limestone. It is the most frequently occurring type of cave. It can also form in other rocks, including chalk, dolomite, marble, salt beds, and gypsum.

Process

Bedrock is dissolved by natural acid in groundwater that seeps through bedding-planes, faults, joints and so on. Over geological epochs these openings expand as the walls are dissolved to become caves or cave systems.

The portions of a solutional cave that are below the water table or the local level of the groundwater will be flooded.

Limestone caves

The largest and most abundant solutional caves are located in limestone. Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation. These include flowstones, stalactites, stalagmites, helictites, soda straws, calcite rafts and columns. These secondary mineral deposits in caves are called speleothems.

Carbonic acid dissolution

Limestone dissolves under the action of rainwater and groundwater charged with H₂CO₃ (carbonic acid) and naturally occurring organic acids. The dissolution process produces a distinctive landform known as karst, characterized by sinkholes, and underground drainage. Solutional caves in this landform—topography are often called karst caves.

Hydrogen sulfide dissolution

Lechuguilla Cave in New Mexico is generally considered the world's most spectacularly decorated cave. Lechuguilla and nearby Carlsbad Cavern are now believed to be examples of another type of solutional cave. They were formed by H₂S (hydrogen sulfide) gas rising from below, where reservoirs of oil give off sulfurous fumes. This gas mixes with ground water and forms H₂SO₄ (sulfuric acid). The acid then dissolves the limestone from below, rather than from above, by acidic water percolating from the surface.

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