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How Caves Form in Limestone

That is such a common question on ‘Answers’ I wrote this single reply! The technical terms are introduced by capital initials.

Most of the world’s caves are in Limestone.

Caves need three materials: a soluble rock like Limestone or Gypsum, water and Carbon-dioxide (CO2).

Their host limestone also needs to be of appropriate physical structure and raised into hills, then subjected to reasonably consistent precipitation for many tens or hundreds of thousands of years.

Limestone is a sedimentary rock of which the world’s greater proportion was laid down in warm, relatively shallow, seas. The rock was laid in horizontal layers – Beds – separated by Bedding-planes which generally reflect geologically-brief changes in the environment. The suite of beds is known as a Formation, generally named after its “type area”.

Later continental uplift (tectonic processes) raise the formation along with its underlying rocks, usually tilting and folding it to at least some extent in the process. Since most rocks are brittle they cannot take much stress, and limestone beds crack into grids of fine fractures called Joints. The uplift and folding often also causes Faulting – major breaks with the rock mass one side of the Fault Plane being raised, lowered or moved horizontally past that on the opposite side. (Note: Plane – the “Fault Line” sometimes misused as a political metaphor is that of the fault-plane cutting the land surface.)

Now we have the hills, next we need rain-water that has absorbed atmospheric CO2 to create Carbonic Acid (weak, natural soda water in fact!). It may be augmented by acids from the soil, too. This solvent permeates through all those joints, bedding-planes and faults; flowing very, very slowly under considerable pressure applied by its depth, from its sinks on the surface to its springs at the base of the formation. In doing so, it dissolves the limestone (chemical weathering), creating meshes of tiny micro-conduits that over many tens of thousands of years coalesce and capture each other to form cave passages.

Once this happens, the rate of erosion can increase – though still to perhaps only a few millimetres per thousand years under generally temperate climates.

A cave, or a series within a cave system, that still carries its formative stream is called “Active”, and is still being developed.

Surface changes such as the valley floor being lowered by erosion, or down-cutting within the cave by its stream, changes the water’s route and the original, now dried-out, stream-way is called “Fossil” or “Abandoned”. Such passages may be filled with silt left by floods as the main flow gradually abandons them; or may become richly decorated with Speleothems – calcite deposits such as stalactites and stalagmites precipitated from ground-water still oozing through the joints in the limestone above the cave. In time such passages may start to break down as there is no stream to dissolve away slabs falling from the roof as permeating ground-water attacks the rock above.

In the end, surface lowering of the landscape as a whole, breaches and destroys the cave. Nothing is permanent in Nature!

Caves in limestone are also parts of Karst Landscape. i.e. a landscape developed by the dissolution of limestone, giving surface features like Dolines, Limestone Pavement, and in the tropics, distinctive hills such as those represented in Chinese Willow-pattern images. ‘Karst’ is from the Slavic word ‘Kras’, the name for its world type-area.

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The above is purely an introduction to a vastly more complex and subtle series of processes, of course, and you need to refer to appropriate text-books on geology and cave studies to learn them.

The scientific study of caves is Speleology – embracing geology, hydrology, Biology, Archaeology and other disciplines.

Simply visiting caves to enjoy them for their scenery and the physical and mental challenges they present, is called Caving, though you can’t study a cave unless you can negotiate its obstacles. The enthusiasts are simply Cavers throughout the English-speaking world – you see “spelunkers” sometimes on ‘Answers’ but it's an old slang word not found in caving literature.

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When limestone dissolves what happenns to the dissolved material?

When limestone dissolves, the dissolved material forms ions, primarily calcium and bicarbonate ions, in the water. These ions can then be carried away by the water through rivers or groundwater. Over time, this process can lead to the formation of caves and sinkholes.


What forms when limestone found in the earth has been eatin away?

When limestone is eaten away, it forms various features such as sinkholes, caves, and underground tunnels. This process occurs due to the dissolution of the limestone by acidic groundwater. The result is the creation of unique and sometimes expansive underground landscapes.


When the roof of a cave wears away and the ground sinks in it forms a what?

When the roof of a cave wears away and the ground sinks in, it forms a sinkhole. Sinkholes are depressions or holes in the ground that are typically caused by the collapse of surface material into underground caves or voids.


Is water in caves acidic?

Water in caves can vary in acidity depending on factors such as the rock composition and interactions with organic matter. In some caves, groundwater can become acidic due to the presence of minerals like sulfuric acid from rock weathering processes. However, not all water in caves is necessarily acidic, and some may be neutral or even slightly alkaline.


What forms when limestone bedrock dissolves under many layers of soil?

When limestone bedrock dissolves under layers of soil, it can lead to the formation of karst landscapes, which include features such as sinkholes, caves, and underground drainage systems. This process occurs due to chemical weathering, primarily involving the reaction between carbonic acid in rainwater and calcium carbonate in limestone. As the limestone dissolves, it creates voids and cavities that can eventually collapse, reshaping the surface landscape. Additionally, the dissolved minerals can contribute to groundwater systems and mineral deposits.

Related Questions

When limestone dissolves what happenns to the dissolved material?

When limestone dissolves, the dissolved material forms ions, primarily calcium and bicarbonate ions, in the water. These ions can then be carried away by the water through rivers or groundwater. Over time, this process can lead to the formation of caves and sinkholes.


What forms when limestone found in the earth has been eatin away?

When limestone is eaten away, it forms various features such as sinkholes, caves, and underground tunnels. This process occurs due to the dissolution of the limestone by acidic groundwater. The result is the creation of unique and sometimes expansive underground landscapes.


What forms when underground layers of limestone are dissolved by ground water?

Karst topography forms when underground layers of limestone are dissolved by groundwater. This process creates unique landforms such as sinkholes, caves, and underground drainage systems. The dissolution of limestone occurs due to its chemical composition and the acidic nature of groundwater.


When limestone on the surface is dissolved by ground water it forms?

When limestone on the surface is dissolved by groundwater, it forms features such as caves, sinkholes, and disappearing streams, through a process known as karst topography. This occurs because limestone is a rock that can easily be dissolved by the slightly acidic nature of groundwater, creating these unique geological formations over time.


What forms when groundwater erodes limestone?

Caves.


What are the three causes of sinkholes in Florida?

Florida has a lot of porous limestone underneath the surface. It can hold lots of water in underground aquifers. As groundwater flows through the limestone, it forms an eroded landscape called karst, known for caves, springs and sinkholes.


How does ground water create certain features?

Groundwater can create certain features on the Earth's surface through erosion and deposition. The slow movement of groundwater can dissolve and carry away rock material, creating caves, sinkholes, and caverns. When groundwater deposits minerals as it flows through the ground, it can form features like stalactites and stalagmites in caves.


How does groundwater create cave?

Groundwater can dissolve rock, typically limestone or dolomite, over time as it flows through cracks and fractures underground. This process forms caves through a combination of chemical weathering and erosion, creating underground voids and passages that we see as caves.


Which is required for karst topography to form?

Karst topography forms in regions with soluble bedrock like limestone or dolomite that is prone to dissolution by groundwater. The presence of abundant rainwater, which is slightly acidic, plays a key role in dissolving the bedrock and creating the unique features of karst landscapes such as sinkholes, caves, and underground drainage systems.


What is formed when groundwater mixes with carbon dioxide from air?

When groundwater mixes with carbon dioxide from the air, it forms carbonic acid. This weak acid can dissolve minerals in the ground and lead to the formation of underground caves, sinkholes, and other karst landscapes over long periods of time.


What is groundwater that forms caves like?

Acidic ground water (rain-water that has absorbed atmospheric carbon dioxide to form carbonic acid) forms caves by dissolving the limestone as it flows through the joints & other discontinuities in the rock mass.


What type of weathering creates karst topography?

Karst topography is created by chemical weathering, specifically by the dissolution of soluble rocks such as limestone and dolomite. This process forms features like sinkholes, caves, and underground drainage systems.