Processes and

Landforms in Limestone

Environment

28/10/2014

Learning Outcome

Describe the characteristics of limestone as a rock

Describe the chemical weathering process of limestone

Factors affecting the development of limestone

landscapes

Account for the importance of limestone environments

LIMESTONE ROCK CHARACTERISTICS

Limestone is a sedimentary rock consisting of more than 50% calcium carbonate (calcite - CaCO3). There are many different types of limestone formed through a variety of processes.

Limestone may form inorganically or by biochemical processes. There are many types of limestone because of the variety of conditions under which it is produced. Coral reefs are examples of limestone produced in the form of the skeletons of the coral invertebrate animals.

Chalk is another form of biochemically produced limestone. Chalk is a soft, porous rock made up of the skeletal parts of microscopic marine organisms. It produces the white cliffs of Dover, England.

Coquina is the name given to limestone in the form of poorly cemented shells and shell fragments.

The stalactites and stalagmites in caves are mostly composed of limestone of inorganic origin. Sometimes called dripstone, this limestone is more formally called travertine.

Another form of limestone of inorganic origin is oolitic limestone, limestone formed from small spherical grains called ooids. These grains form on small particles suspended in shallow marine waters.

Carboniferous limestone is an example of a pervious rock, as it allows water to flow through the joints and bedding planes. This is a well-cemented rock of low porosity, and occurring in thick beds. As they have prominent vertical joints, they can be easily spilt into blocks for use as building stone. It is a very tough rock, and is commonly used as roadstone, but can also be used for cement making because it is often quite pure, and as a source of calcium carbonate for the chemical industry.

Limestone rock dissolves slowly in carbonic acid (carbon dioxide and rainwater) creating a range of distinctive landforms.

Most weathering takes place between the blocks where the acidic rainwater can penetrate: The main processes, which affect it, are carbonation and solution.

Due to the pervious nature of the rock, drainage is usually underground and can only be seen where the limestone meets an area of impermeable rock. This process can be seen in the appearance of natural springs and is known as resurgence.

CHEMICAL WEATHERING PROCESS OF

LIMESTONE

Weathering or denudation in a limestone region is affected by carbonation, and this process is fundamental to the understanding of the region's physical geography.

Limestone, or calcium carbonate (CaCO3), is a sedimentary rock formed by the compressing of the remains of dead sea creatures.

Weathering of the rock is made easy by the fact that limestone contains bedding planes (horizontal cracks) and joints (vertical cracks) allowing water to pass through the rock. The chemical weathering of limestone, or carbonation, occurs when the rock is attacked by rainwater. This occurs when rain takes in carbon dioxide as it passes through the atmosphere. Carbon dioxide (CO2) dissolves in rainwater (H2O) then forms weak carbonic acid (H2CO3)

Carbonic acid is especially effective at dissolving limestone. It reacts with the calcium carbonate (CaCO3) in the limestone. This forms calcium bicarbonate (Ca(HCO3)2), which is soluble in water. This solution percolates through rock. It removes the calcium carbonate. When the carbonic acid seeps through limestone underground, it can open up huge cracks or hollow out vast networks of caves. 

The chemical equation for this process is CaCO3+ H2CO3 = Ca(HCO3)2, i.e., Limestone + Carbonic acid

(rainwater) = Calcium Bicarbonate (soluble limestone)

FACTORS AFFECTING THE DEVELOPMENT OF

LIMESTONE LANDSCAPES

FACTORS AFFECTING LIMESTONE LANDSCAPES

Purity

Solubility of Limestone - percent calcite

Climate - Temperature and Moisture

Structure and Lithology - joints, fractures, porosity

Water

Vegetation- acidity (pH) of groundwater

Atmospheric CO2 - affects solubility of Carbonates

Time

FACTORS AFFECTING LIMESTONE LANDSCAPES

Purity

Solubility of Limestone - percent calcite

Climate - Temperature and Moisture

Structure and Lithology - joints, fractures, porosity

Water

Vegetation- acidity (pH) of groundwater

Atmospheric CO2 - affects solubility of Carbonates

Time

IMPORTANCE OF LIMESTONE

ENVIRONMENTS

IMPORTANCE OF UNDERSTANDING KARST SYSTEMS

Karst landscapes make up about 10% of the Earth’s surface

They are most abundant in tropical humid regions but also

occur in temperate, tropical, alpine and polar environments

A quarter of the world’s population depend on water

supplied from karst areas

However, karst systems are vulnerable to groundwater

pollution due to the relatively rapid water flow and the lack

of a natural filtration system

Local drinking water supplies risk being contaminated as a

result

PROTECTING KARST RESOURCES IN THE CARIBBEAN

The Caribbean has one of the world’s premier karst landscapes (which make up more than half of the total land area of the region)

About 90% of the karst is in the Greater AntillesOther significant areas are in the Bahamas,

Anguilla, Antigua, the Cayman Islands, the Virgin Islands, Guadeloupe, Barbados, Trinidad and Tobago, and the Netherlands Antilles

Most countries have adopted conservative strategies in the establishment of parks, reserves and sanctuaries encompassing karst landscapes

Regionally, there are 121 protected karst areas, covering 14.3% of the total karst

Economic value of karst1. Agriculture

• Some karst regions have rich and highly productive soils

• The caves may be used for specialised agricultural activities such as fish breeding, mushroom growing and cheese production

• In Southeast Asia, limestone caves are an important source of bird’s nest

2. Industry• Limestone is an important raw material for

steel-making and cement• It is also used to reduce some forms of

industrial pollution, e.g. by removing sulphur dioxide from gases

3. Tourism• Annually, about 20

million people worldwide visit limestone caves

• The Green Grotto Caves in Jamaica, Harrison’s Cave in Barbados and Gasparee Caves in Trinidad are tourist attractions

• Tourism is an important source of income for the residents in karst areas

Harrison's Cave

Gasparee Caves

Scientific value of karstKarsts are a key source of information on landform

evolution and climate changeThe caves contain important archaeological and

palaeontological materialKarsts host various endangered plant and animal

species, both underground and on the surface

Recreational value of karstKarsts offer opportunities for caving, which has

become a popular recreational activityThis contributes to tourism

THREATS TO KARST SYSTEMSDrawing of water within karst areas disturbs

the hydrological systemThe water level and the water quality are

threatenedMoisture within the cave microclimate is

affectedThe plant and animal species in the caves are

subsequently affectedQuarrying for precious minerals such as bauxite

destroys the cavesDumping of sewage and domestic and

industrial waste can lead to groundwater pollution as there is little natural filtration in karst regions