The caves

The caves are widespread on earth. People have found only a small part of them, but for the time being, very few have been studied. Caves arise mainly in the "soluble" rocks: limestones, gypsum, anhydrite, mineral salts. Other rocks, such as granites, are incomparably more resistant to weathering and the destructive effects of underground groundwater. Therefore, in them caves practically do not arise. The largest are complex systems of passageways and halls, often with a total length of up to several tens of kilometers. Caves - the object of studying speleology. A considerable contribution to the study of them makes speleoturists. Caves in the entrance part, with suitable morphology (horizontal spacious entrance) and location (close to the water) were used by ancient people as comfortable dwellings.

The caves are widespread on earth. People have found only a small part of them, but for the time being, very few have been studied

"Soluble" rocks cover huge areas: carbonate (limestone, dolomite and chalk) up to 40 million km², gypsum and anhydrite up to 7 million km², and rock salt and other salts up to 4 million km².

All phenomena of chemical and partly mechanical impact of groundwater on such rocks are called just karst. Tectonic cracks and faults play an enormous role in the formation of caves. From the maps of the caves examined, it can often be seen that the courses are confined to tectonic disturbances that can be traced on the surface.

Water not only dissolves them and takes out dissolution products, but also deposits substances. The vaults collapse, the size of the underground cavities increases even more. There are karst forms of relief: funnels, precipices, wells, caves (horizontal, inclined and vertical). Their form is diverse. In labyrinths, "bottomless" crevices and vertical wells, human life has been cut short. Even speleologists, people who are exploring caves equipped with special equipment are sometimes awaited by tragic surprises...

Underground waters are not only cold. Often they are heated to a considerable temperature. In this case, a thermokarst occurs. Calcite and gypsum are the most common building minerals in the cave. Barite, aragonite, strontianite and celestite are less common here. On Earth there is no more favorable place to study the natural crystallization of minerals than caves. Cave waters are only part of a vast "ocean" of underground, groundwater, filtered from the surface of the Earth.

Caves by their origin can be divided into five groups: tectonic, erosion, ice, volcanic and the largest group, karst.

Tectonic caves can occur in any rocks as a result of the formation of tectonic faults. As a rule, they occur in the sides of the deep valleys, deeply embedded in the plateau, when huge rock masses break off from the sides, forming cracks of sinking (sherlops). Cracks of settling usually converge with depth with a wedge. Most often, they are covered with loose deposits from the surface of the massif, but sometimes they form quite deep vertical caves with a depth of up to 100 m.

Erosion caves are formed in insoluble rocks due to mechanical erosion, that is, worked with water containing grains of solid material. Often they are formed on the seashore under the influence of the surf, but they are not large. However, it is possible the formation and caves, worked through the primary tectonic cracks, leaving streams under the ground. There are quite large (hundreds of meters long) erosion caves formed in sandstones and even granites.

Glacial caves are formed in the body of glaciers melted water. Such caves are found on many glaciers. Thawed glacial waters are absorbed by the body of the glacier along large cracks or at the intersection of cracks, forming passages sometimes traversed by humans. The length of such caves can be several hundred meters, depth - up to 100 m and more.

Volcanic caves occur during eruptions of volcanoes. The stream of lava, cooling down, is covered with a hard crust, forming a lava tube, inside which the molten rock still flows. After the eruption has already, in fact, ended, the lava flows out of the tube from the lower end, and inside the tube remains a cavity. It is clear that lava caves lie on the surface, and often the roof collapses. In addition to lava tubes, there are vertical volcanic caves - the crater volcanoes.