A. limestone is below the water table, then lowering of the water table, then water dripping from the ceilingB. lowering of the water table, then water dripping from the ceiling, then limestone is below the water tableC. water dripping from the ceiling, then lowering of the water table, then limestone is below the water tableD. none of the above
Solutional caves are the most frequently occurring caves and such caves form in rock that is soluble, such as limestone, but can also form in other rocks, including chalk, dolomite, marble, salt, and gypsum. Rock is dissolved by natural acid in groundwater that seeps through bedding-planes, faults, joints and so on. Over geological epochs cracks expand to become caves or cave systems. The largest and most abundant solutional caves are located in limestone. 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. Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation. These include flowstones, stalactites, stalagmites, helictites, soda straws and columns. These secondary mineral deposits in caves are called speleothems. The portions of a solutional cave that are below the water table or the local level of the groundwater will be flooded. The world's most spectacularly decorated cave is generally regarded to be Lechuguilla Cave in New Mexico. 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.
