Caves are formed by various geologic processes and can be the cave and the light pdf sizes. These may involve a combination of chemical processes, erosion from water, tectonic forces, microorganisms, pressure, and atmospheric influences. Isotopic dating techniques can be applied to cave sediments, in order to determine the timescale when geologic events may have occurred to help form and shape present day caves. Caves can be classified in various other ways as well, including active vs.
Over time cracks enlarge to become caves and cave systems. The largest and most abundant solutional caves are located in limestone. The acid then dissolves the limestone from below, rather than from above, by acidic water percolating from the surface. Hot liquid lava continues to flow under that crust, and if most of it flows out, a hollow tube remains. Lava caves include but are not limited to lava tubes. Other caves formed through volcanic activity include rift caves, lava mold caves, open vertical volcanic conduits, and inflationary caves. 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. Corrasional or erosional caves are those that form entirely by erosion by flowing streams carrying rocks and other sediments. These can form in any type of rock, including hard rocks such as granite.
Generally there must be some zone of weakness to guide the water, such as a fault or joint. A subtype of the erosional cave is the wind or aeolian cave, carved by wind-born sediments. Many caves formed initially by solutional processes often undergo a subsequent phase of erosional or vadose enlargement where active streams or rivers pass through them. Glacier caves are formed by melting ice and flowing water within and under glaciers. 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 of stone.