Formation of karst cave

CaCO3 Calcium carbonate has the property that when it meets water with dissolved CO2, it will become soluble calcium bicarbonate [Ca (HCO3) 2] CaCO3+CO2+H2O = Ca (HCO3) 2. If the water in which calcium bicarbonate is dissolved is heated or the pressure is suddenly reduced, the calcium bicarbonate dissolved in water will decompose and become calcium carbonate again. While releasing carbon dioxide. Ca (HCO _ 3) _ 2 = CaCO _ 3 ↓+CO2 ↑+H2O, the above reactions occur constantly in nature, thus forming various landscapes in caves.

The formation of karst caves is the result of long-term dissolution of groundwater in limestone areas. Insoluble calcium carbonate in limestone can be converted into slightly soluble calcium bicarbonate under the action of water and carbon dioxide. Due to the different calcium content and erosion degree of each part of limestone layer, it is gradually dissolved and divided into independent, changeable, steep and beautiful peaks and caves, and the landscape is strange. For example, the world-famous Guilin Cave and Beijing Shihua Cave are masterpieces created by the slow erosion of water and carbon dioxide. When water dissolved with calcium bicarbonate drips from the top to the bottom of the cave, the solubility of carbon dioxide will decrease and calcium carbonate will be precipitated due to the evaporation of water or the decrease of pressure and the change of temperature. After millions of years of accumulation, these sediments gradually formed stalactites, stalagmites and so on. If water with dissolved calcium bicarbonate drips from the top of the cave, with the evaporation of water and carbon dioxide, the precipitated calcium carbonate will accumulate into stalactites, stone curtains and stone flowers. When stalactites at the top of the cave are connected with stalagmites on the ground, strange stone pillars will be formed.

In nature, rainwater containing dissolved carbon dioxide will partially dissolve limestone strata and convert calcium carbonate into soluble calcium bicarbonate.

Calcium carbonate+carbon dioxide +H2O = calcium bicarbonate 2

When heating or pressure drops suddenly, the dissolved calcium bicarbonate will decompose and become calcium carbonate precipitation again.

Ca(HCO3)2==== CaCO3↓+CO2↑+H2O

Nature has repeatedly repeated the above reactions for a long time. Thus, various strange and spectacular caves are formed, such as Seven Star Rock in Guilin, Seven Star Rock in reed flute cave and Zhaoqing. There are various stalactites and stalagmites in the cave, which are formed by calcium carbonate deposited after decomposition of calcium bicarbonate.

Natural river water or well water often contains impurities such as calcium bicarbonate, magnesium bicarbonate, calcium sulfate and magnesium sulfate. If the content is large, this kind of water is called hard water. Hard water is not suitable for industrial water, because it will be decomposed by heat in the boiler, leading to poor heat conduction, waste of fuel and even accidents. Hard water is not suitable for drinking either. Long-term drinking will cause digestive system and urinary system diseases. Washing clothes with hard water has poor washing effect.

Karst refers to the landform where soluble rocks, especially carbonate rocks (such as limestone and gypsum) are dissolved and sometimes deposited by running water containing carbon dioxide. They are usually strange in shape, including caves, stone buds, stone gullies, stone forests, caves, underground rivers and cliffs. There are often many strange peaks in this landform area.

This landform is found in Guangxi, Yunnan, Guizhou and other places in China. This is how the grotesque grottoes presented by the famous Guilin landscape were formed.

Formerly known as karst, it originated from a place name in the former Yugoslavia.

Surface water plays an important role in the erosion of sediments or rocks passing by during the movement, including the transportation of debris under the action of hydrodynamic force, the chemical dissolution of rocks or sediments by water, and the abrasion of debris during transportation. Karst landform is the result of groundwater erosion on carbonate rocks. Under the action of water flow, steep coast, curved gullies, suspended valleys with high ice erosion and magnificent grand canyons have been formed. "Drops of water pierce the stone" is also a portrayal of the chemical erosion of water.

The formation of karst caves is the result of long-term dissolution of groundwater in limestone areas. The main component of limestone is calcium carbonate (CaCO3), which reacts with carbon dioxide in the presence of water to generate calcium bicarbonate [Ca(HCO3)2], which is soluble in water, so it forms a cavity and gradually expands. This phenomenon is most typical in the karst plateau along the Adriatic Sea in Yugoslavia, so this terrain in limestone area is often called karst terrain.

According to its development and evolution, karst can be divided into the following six types.

1) Surface water dissolves along the joint surface or fracture surface in limestone, forming a karst ditch (or karst trough), and the limestone originally distributed in layers is divided into stone pillars or stalagmites by the karst ditch.

2) Surface water permeates and dissolves downward along limestone cracks, and a sinkhole is formed when the depth exceeds100m. ..

3) The groundwater falling from the sinkhole flows laterally to the aquifer, forming a karst cave.

4) With the formation of underground caves, the surface collapses, and those with large collapse depth and small area are called collapse funnels, while those with small depth and large area are called collapse ponds.

5) Long-term joint action of groundwater dissolution and collapse forms slopes and valleys and natural bridges.

6) When the ground rises, the original caves and underground rivers are taken out of the ground and turned into dry valleys and stone forests, and the dissolution of groundwater continues under the old caves and underground rivers. The stone forest in Lunan, Yunnan Province is the product of the first stage (ditch-dissolving stage), and the natural scenery here is particularly charming because of the touching legend of Ashima girl. Elephant trunk mountain in Guilin was formed when the primitive underground river was exposed to the surface. In Guangxi, you can often see this kind of cave exposed to the surface, commonly known as "fairy mirror" or "fairy mirror".

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