Limestone Landscapes: Processes (SQA National 5 Geography): Revision Note

Specification checklist

This page covers what you need to know from the SQA National 5 geography specification to answer questions on:

• Landscape types

  • Limestone - limestone pavements, potholes/swallow holes, caverns, stalactites and stalagmites, intermittent drainage

Processes of limestone erosion

• Limestone is a sedimentary rock

• Layers of sediment are compacted together until they become solid rock

  • Limestone is formed from the tiny shells and skeletons of dead sea creatures

• Solution is the main type of erosion

  • The main chemical component of limestone is calcium carbonate (alkali)

  • Rainwater is a weak carbonic acid, which reacts with the calcium carbonate

  • Limestone, therefore, dissolves by carbonation weathering

  • Rock particles are washed away in solution

Formation of a limestone pavement

• Limestone was laid down in horizontal layers called beds, separated by bedding planes

  • It contains vertical cracks called joints

• Acidic rainwater is a weak carbonic acid

  • This reacts with limestone as it passes through the permeable rock, dissolving it

  • The joints become deeper and wider to form gaps called grykes

• In between the grykes are rectangular blocks of limestone called clints

  • The resulting pattern of block-like rock is called a limestone pavement

Formation of potholes/swallow holes

• Surface streams or rainwater do not flow far over exposed limestone as they rapidly seep into the rock.

  • When the water flows over the limestone, it enlarges the joints in the rock through chemical weathering called solution and carbonation

  • Water can therefore easily seep through the rock layers. 

• Eventually, a surface stream will disappear down a hole and flow along underground channels.

  • The resulting hole in the surface of the landscape is called a swallow hole (potholes)

Formation of stalactites and stalagmites

• When water flows underground, it contains dissolved limestone called calcium carbonate

• Water may drip from the roof of a cavern

• When this happens, some water evaporates and tiny amounts of solid calcite are deposited on the cavern roof

  • These deposits build up over a very long period and form features called stalactites, which hang down from the ceiling of a cavern

  • Some of the water dripping from the roof of the cavern may also drop on the floor, where it evaporates

  • The splash spreads the deposit of calcite on the cavern floor to create short and stumpy features called stalagmites

• Occasionally, stalagmites and stalactites meet to form a rock pillar 

Intermittent drainage

• If limestone has a layer of impermeable rock above it, then it is capped

  • Surface streams form because the water cannot infiltrate

• When the surface streams reach limestone, the water will disappear from the surface, as limestone is permeable

  • This will occur because water may seep through joints, or streams may disappear down swallow holes

• The underground stream will flow down through the limestone until it reaches impermeable rock

  • It will re-emerge at the surface (called a resurgence) because it cannot flow through the rock below.