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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 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 Antilles Other 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 karst 1. 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 karst Karsts are a key source of information on landform evolution and climate change The caves contain important archaeological and palaeontological material Karsts host various endangered plant and animal species, both underground and on the surface Recreational value of karst Karsts offer opportunities for caving, which has become a popular recreational activity This contributes to tourism THREATS TO KARST SYSTEMS Drawing of water within karst areas disturbs the hydrological system The water level and the water quality are threatened Moisture within the cave microclimate is affected The plant and animal species in the caves are subsequently affected Quarrying for precious minerals such as bauxite destroys the caves Dumping of sewage and domestic and industrial waste can lead to groundwater pollution as there is little natural filtration in karst regions