Sequatchie Cave Earthcache EarthCache

Secondary caves are formed inside the rock after the rock itself has formed by processes such as solution and erosion.

Sea caves are found along coasts around the world. A special case is littoral caves, which are formed by wave action in zones of weakness in sea cliffs. Often these weaknesses are faults, but they may also be dykes or bedding-plane contacts. Some wave-cut caves are now above sea level because of later uplift. Elsewhere, in places like Thailand's Phang Nga Bay, solutional caves have been flooded by the sea and are now subject to littoral erosion. Sea caves are generally around 5–50m in length but may exceed 300m.

Glacier cave in Big Four Glacier, Big Four Mountain, Washington, ca. 1920.Glacier caves occur in ice and under glaciers, formed by melting. They are also influenced by the very slow flow of the ice which tends to close the caves again. (These are sometimes called ice caves, though this term is properly reserved for caves which contain year-round ice formations). Solutional caves may form anywhere with rock which is soluble, and are most prevalent in limestone, but can also form in other material, including chalk, dolomite, marble, granite, salt, sandstone, fossilized coral and gypsum. The most common process of cave formation is karstification, which is the solution of rocks by rain water. Fracture caves are formed when layers of more soluble minerals such as gypsum dissolve out from between layers of less soluble rock. These rocks fracture and collapse in blocks. Talus caves are the openings between rocks that have fallen down into a pile, often at the bases of cliffs.

Speleothems in Hall of the Mountain Kings, Ogof Craig a Ffynnon, South Wales.Anchihaline caves are caves, usually coastal, containing a mixture of freshwater and saline water (usually sea water). They occur in many parts of the world, and often contain highly specialized and endemic faunas. 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, sinking streams, and underground drainage. Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation, including the most common and well-known stalactites and stalagmites. These secondary mineral deposits in caves are called speleothems. The world's most spectacularly decorated cave is generally regarded to be Lechuguilla Cave (New Mexico, USA).

Lechuguilla and nearby Carlsbad Caverns are now believed to be examples of another type of solutional cave. They were formed by acid rising from below, where reservoirs of oil give off sulfurous fumes, rather than by acidic water percolating from the surface.