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Physical Geography: Karst Landscapes - Coggle Diagram
Physical Geography: Karst Landscapes
Area of exposed limestone
Effects of chemical weathering
Permeable nature of limestone
Carbon dioxide mixes with rainwater, makes weak carbonic acid
Dissolves calcium carbonate in limestone, weakens and widens joints and bedding planes
Limestone pavement, freeze-thaw action active on exposed rock
Processes: carbonation, solution
Exposed area of limestone
Surface karst feature
Rugged and bare landscape with flat areas of rock surface
Carbonation active
Dissolves permeable limestone, creating clints and grikes
Hollows called karren form on the surface of clints
Fluting occurs when the water runs off the edge
Joints further enlarged by hydraulic action and abrasion
Lack of surface drainage features
The Burren, Co. Clare
Covers approximately 360 km2 of north-west Co. Clare
Formed during the carboniferous period, 350 MYA
Formed of limestone rock plateau
Features include
Limestone pavements
Subsurface and dripstone features
Example: Aillwee Cave, Poulnabrone dolmen
Swallow holes, e.g. Pollnagollum in the Burren, Co. Clare
Processes: carbonation, solution, hydraulic action, abrasion
River disappears underground
River flows over area of impermeable rock until it reaches area of permeable rock such as limestone
Grikes enlarge overtime
River swallowed underground
Dry valley left downstream
When river reappears at the surface, it is called a river of resurgence
Other surface features: dolines, turloughs, limestone terraces
Subsurface landforms
Caves, e.g. Aillwee Cave, Burren
Processes: carbonation, hydraulic action, abrasion, solution
Cave or cavern opening underground
Enlarged by underground rivers
Caves form below zone of saturation
Carbonation, hydraulic action, solution and abrasion all active
If the water table drops, new caves will form at lower levels
Old dry caves often become tourist attractions
Dripstone features, e.g. Aillwee Cave, Burren
Processes: carbonation, solution
Stalactites, stalagmites, pillars, curtains, straws
Carbonation is active on permeable limestone
Tiny specks of calcite are left behind
Stalactites – icicle-shaped mineral formations that hang from the ceiling
Stalagmites form on the floor below, and are often wider due to splash effect
If they meet, pillars/columns form
If droplets run along a crack in a thin sheet they form a curtain
If thin hollow tubes form on the cave ceiling they are called straws
The cycle of erosion in a karst topography
Three stages:
Youthful
Rivers flowing on the surface
Erosion of impermeable rock
Then erosion of permeable rock (limestone)
Chemical weathering (carbonation)
Formation of swallow holes
Mature
Dry valleys on the surface
Rivers have disappeared underground
Roof of caves collapse, creating dolines
If these dolines join, they create larger depressions called uvalas
Old age
Weathering
Almost complete removal of limestone
Older more resistant rock left prominent – hums
Rivers once again flow over the surface