Asolutional cave,solution cave, orkarst cave is acave usually formed in a soluble rock likelimestone (Calcium carbonateCaCO3). It is the most frequently occurring type of cave. It can also form in otherrocks, includingchalk,dolomite,marble,salt beds, andgypsum.[1]
Bedrock is dissolved bycarbonic acid in rainwater,groundwater, orhumic acids from decaying vegetation, that seeps throughbedding planes,faults,joints, and the like. Over time, the surface terrain breaks up intoclints separated by grikes and punctuated bysinkholes into which streams may disappear, crevices expand as the walls are dissolved to become caves or cave system. These may turn into large caverns ordolines when the roof collapses.[2]
The portions of a solutional cave that are below thewater table or the local level of the groundwater are flooded.[3]
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The largest and most abundant solutional caves are located in limestone. Limestone caves are often adorned withcalcium carbonate formations produced through slow precipitation. These includeflowstones,stalactites,stalagmites,helictites,soda straws,calcite rafts, andcolumns. These secondary mineral deposits in caves are called "speleothems".[2][5][6]
Limestone dissolves under the action of rainwater and groundwater charged with H2CO3 (carbonic acid) and naturally occurringorganic acids. The dissolution process produces a distinctive landform known as "karst", characterized bysinkholes and underground drainage. Solutional caves in this landform—topography are often called karst caves.
Lechuguilla Cave inNew Mexico and nearbyCarlsbad Caverns 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 ofpetroleum 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 to the surface.
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