Weathering (Karst landscapes)

Surface features in karst landscapes

1. Limestone pavements

2. Swallow holes

3. Disappearing streams

4. Dolines/sinkholes

Underground features of karst landscapes

1. Stalactite

2. Stalagmite

3. Pillars

4. Curtains

Limestone pavements

• Limestone pavements are extensive areas of flat limestone rock.

• The first soil cover must be removed. Then the limestone is then chemically weathered by carbonation.

• Rainwater mixes with CO² and forms a weak carbonic acid. When it falls on exposed limestone, it dissolves the calcium carbonate that keeps the rock together.

• Percolating through the permeable limestone, the carbonic acid attacks joints in the rock.

• The joints are widened and spread, making gaps in the limestone (grikes).

• Rocks of limestone called clints remain on the surface, seperated by grikes.

Swallow holes

• Swallow holes are large openings formed in river beds in limestone areas.

• Streams can erode the vertical joints/grikes in the permeable limestone via hydraulic action, abrasion and solution.

Disappearing streams

• Disappearing streams are streams of water that instantly disappear underground via swallow holes.

• They play a big role in the formation of caves and caverns underground.

Dolines/Sinkholes

• Dolines are deep hollows formed on the ground surface when a cave roof collapses.

• When a limestone cave grows upwards, layers of rocks can become too weak to support itself.

Stalactites

• Stalactites are underground features of a karst landscape that form on the roof of caves. It’s a build up of calcium carbonate deposits that grow down from the cave roof.

• A limestone feature formed in an underground cave is known as speleothem.

• The stalactites form when water filled with dissolved calcium carbonate which is known as calcite percolates through the limestone layers until it reaches the area filled cave.

• The water drips down slowly from a narrow joint opening on the cave ceiling.

• Once the water comes into contact with air-filled cave it makes a chemical reaction and reverses the original chemical reaction, forming new calcium carbonate.

• The water continues dripping down till it forms stalactites and stalagmites.

Stalagmite

• As calcium bicarbonate falls from stalactites, evaporation also affects it as it falls leaving behind calcite.

• The calcite accumulates overtime forming stalagmites that grow upwards and are larger and stronger.

Pillars

• Pillars or columns are formed when stalactites and stalagmites grow so huge they join together.

Curtains

• Curtains are formed when calcite deposits form a continuous, narrow but solid structure hanging from a cave roof. They grow down with age.