Limestone

 

You are required to be able to explain the formation of underground and surface limestone features. You will also be required to identify various features on an O.S map.

Checklist

  • Name examples of Limestone areas in the British Isles.
  • Describe the factors that influence limestone scenery: rock structure, permeability & carbonation and solution
  • Explain, with the aid of a diagram and reference to appropriate processes the following Surface Features… Limestone Pavements, Shakeholes, Swallowholes, Potholes
  • Describe and explain the occurrence of Intermittent Drainage.
  • Explain, with the aid of a diagram and reference to appropriate processes the following Underground Features…Caves, Gorges, Stalagmites, Stalactites, Limestone Pillars, Gours.
  • Explain, with the aid of a diagram and reference to appropriate processes, the formation of Glaciokarstic Features such as Scars
  • Identify features on O.S

Some Key Terms

  • Carbonation – Carbon dioxide and rainwater combine to form a weak acid, when this falls on limestone the rainwater reacts with the calcium carbonate in the limestone to form calcium bicarbonate, which is soluble and the limestone becomes weathered.
  • Clints – Large blocks of limestone in limestone pavements.
  • Gorges – Steep sided gap in the landscape. Can form when the roof of a cavern collapses or can be the result of erosion by meltwater streams.
  • Grykes – Deep joints that separate large blocks of limestone in a limestone pavement (clints). Formed by chemical weathering.
  • Impermeable – Water cannot pass through impermeable rock.
  • Intermittent Drainage – Streams flow over surface of impermeable rock then disappear when they meet permeable limestone. The drainage is interrupted.
  • Karst – Exposed limestone clearly seen on the surface is often referred to as karst scenery.
  • Limestone Pillar – As the name suggests this is a pillar of limestone found in underground caves. It occurs when stalagmites and stalactites join.
  • Permeable – Water can pass through the rock e.g. limestone
  • Scars – Steep exposed outcrop of limestone, due to exposure it faces weathering through the processes of frost-shattering resulting in rockfalls and scree slopes.
  • Stalactites – Found hanging from the roof of a cavern, these are deposits of calcite formed due to water evaporating and leaving behind these deposits in an ‘icicle’ shape.
  • Stalagmites – Found on the floor of a cavern, these are deposits of calcite formed due to water dripping onto the floor and evaporating to leave behind deposits of limestone that grow upwards.

Example Exam Questions

  1. Describe the evidence that suggests that area A (shown on map), is an area of Carboniferous Limestone. (8 marks). Tips: Identify various features shown on the map and ensure you name them and provide grid references, you can also make general comments about the area that suggests it is limestone.
  2. Choose one of the carboniferous limestone features you mentioned in Q1, and with the aid of annotated diagrams, explain its formation. (6 marks) Tips: Ensure you include a fully annotated diagram, include the processes involved e.g. explain the process of carbonation, and ensure your written answer is well structured and takes the reader through the formation process step by step.

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