تويت
Primary cave ,Solutional cave
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, includingchalk, 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 bysinkholes, and underground drainage. Limestone caves are often adorned withcalcium carbonate formations produced through slow precipitation. These includeflowstones, 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.[1]The world's most spectacularly decorated cave is generally regarded to beLechuguilla 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.
Some caves are formed at the same time as the surrounding rock. These are sometimes called primary caves.Lava tubes are formed through volcanic activity and are the most common 'primary' caves. The lava flows downhill and the surface cools and solidifies. The hotter lava continues to flow under that crust, and if most of the liquid lava beneath the crust flows out, a hollow tube remains, thus forming a cavity. Examples of such caves can be found on the Canary Islands, Hawaii, and many other places. Kazumura Cave near Hilo is a remarkably long and deep lava tube; it is 65.6 km long (40.8 mi).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.
