Underground caves are typically formed by the dissolution of rock by water containing carbon dioxide, creating cavities. Their evolution can continue through the action of water that sculpts and enlarges the cavities over time.
Caves are formed when rainwater, slightly acidic, seeps through rock for a long time. This water slowly dissolves certain rocks, especially those composed of limestone, giving rise to underground cavities. Little by little, these tiny spaces grow, connect, and form increasingly vast underground passages. This phenomenon occurs mainly in areas where the subsoil is rich in carbonate rocks, namely limestones or dolomites. Sometimes, it is not slow dissolution but rather physical erosion that creates caves, as in cases where rivers or waves carve into softer rocks. Some caves even appear as a result of cooled lava flows that leave behind solid natural tunnels.
Most underground caves are formed through the action of water, especially when it seeps into the ground. As it flows underground, water collects carbon dioxide (CO2), turning into a slightly acidic solution. Over time, this mildly acidic water gradually erodes certain rocks like limestone or gypsum. This is known as chemical erosion. Sometimes, caves also emerge due to mechanical erosion: vigorously flowing water digs, tears away, and transports sediments, widening the passages. More rarely, volcanic processes or even tectonic movements cause the formation of underground cavities. But overall, it's primarily a story of water patiently doing its work beneath our feet!
Some caves, the most well-known, are karst caves, formed by the action of water that gradually dissolves limestone. You mostly find spectacular stalactites and stalagmites there. Others, called volcanic caves, form when lava hardens on the surface while hot lava continues its path below, leaving tunnels behind. Additionally, there are glacial caves, carved by meltwater in ice, often beautiful and bluish. Finally, some caves are created by marine erosion: they are called marine caves, sculpted by waves on rocky coastlines. Each has its own particular style that mainly depends on its origin, climate, or the rocks present.
Several elements influence the evolution of underground caves. The quantity and acidity of infiltrated water play a significant role, as it is responsible for dissolving the rock and gradually enlarging the cavities. The type of rock also matters a lot: some, like limestone, erode easily, while others withstand the test of time better. The climate and regular weather changes directly affect the rates of water infiltration, speeding up or slowing down the formation of a cave. Finally, one can also point to the initial geological structure: faults, cracks, or existing fractures facilitate and direct the development of underground cavities.
Initially, it is primarily rainwater, filled with carbon dioxide absorbed at the surface, that seeps into the ground and slowly attacks the limestone. Over time, small cracks become larger, gradually deepening and forming narrow galleries. Little by little, these galleries expand, the water continues to dissolve the rock, and the spaces sometimes transform into large chambers or deep cavities. Later on, mineral-laden water slowly drips from the ceiling or along the walls, depositing these minerals and forming characteristic structures such as stalactites and stalagmites. Eventually, once the water changes course or drops in level, the cave stabilizes; the mineral formations may continue to develop slowly, sometimes not, and the cavity becomes accessible, more or less permanently, to other natural phenomena or living organisms.
The deepest known chasm today is the Veryovkina Cave in Georgia, which reaches a staggering depth of over 2,200 meters, equivalent to about seven stacked Eiffel Towers!
The longest cave discovered to date is Mammoth Cave, located in the United States in Kentucky. It has over 650 kilometers of explored passages, and new galleries continue to be discovered there every year!
Some creatures have evolved exclusively in underground caves: they have neither eyes nor pigmentation, like certain species of fish and salamanders, fully adapted to this dark environment.
In caves, the temperature remains stable throughout the year, generally around the regional average annual outdoor temperature. This thermal stability explains why, historically, humans have used them as places for storage or refuge.
The diversity of rock formations, such as stalactites, stalagmites, and columns, is linked to various factors: the mineralogical composition of the rocks, the climatic conditions of the region, the flow rate of the water, and the time elapsed during which they formed. These factors influence the size, shape, and diversity of the concretions that can be admired in an underground cave.
Sure. Here’s the translation: "Yes. Some caves harbor a diverse fauna, perfectly adapted to this dark and humid environment. For example, one can find bats, depigmented fish, amphibians, as well as various insects and microorganisms that are specific to caves, known as troglobitic organisms."
Even if the water found in some caves appears to be pure, it is not always safe to drink. This water may contain bacteria, excessive concentrations of minerals, or contaminants from the surface. It is essential to treat or test the water before direct consumption.
Some external indicators can signal the presence of an underground cave, such as collapses, sinkholes (circular depressions), emerging underground springs, or visible openings on cliff faces. However, only a thorough examination conducted by specialists can definitively confirm the actual existence of a significant underground cavity.
No. Although many caves are equipped and secured for visitors, some natural caves pose serious risks: risks of falls, sudden flooding, or disorientation. It is recommended to always visit caves with an experienced guide and to follow all necessary safety precautions.
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