C2 Karsts

Formation of karsts

1. Carbonation

   1. CO2 dissolves in rainwater to form carbonic acid

   2. Carbonic acid dissolves limestone, bicarbonate removed in solution

2. Surface solution of limestone

   1. Weathering and water erosion at the surface causes surface solution of limestone

   2. Limestone has to low porosity (spaces) but high perviousness (permeability) so that water flows along joints and bedding planes to widen these lines of weakness

3. Underground solution

   1. Precipitation that infiltrates and percolates forms groundwater, cause water table to rise

   2. Geomorphic processes widen joints and bedding planes to form karst landforms over time

4. Reprecipitation

   1. Water from solution of limestone contains high concentration of dissolved limestone

   2. When water emerges into cave, CO2 diffuses out and water crystallises on rock surfaces of cave, leading to stalactites and stalagmites

Dolines (aka sinkholes)

• Natural depressions that form when water-saturated soil becomes too heavy, roof of existing voids in soil collapses

• Weathering of limestone beneath the surface, associated slumping of soil into the space created

Cockpit / Cone Karsts

• Roughly equally spaced conical hills and deep dolines

• Forms a continuous terrain of steep slopes and significant relief

• Egg box topography (star shaped depressions)

Formation

• Found mainly in humid tropics

• Rapidly decomposing vegetal matter increases acidity of water, leads to rapid enlargement of dolines

• Water erosion by streams occur along joints, streams flow towards lowest depression

• In humid tropics, water table tends to be shallow and enlarges laterally more than deepen

Tower Karsts

• Towers are steep, big, have height-diameter ratio

• Common feature is sharp rise from surrounding plains

Formation

• Develops when cockpit karsts undergo further weathering and erosion, lowering the floor vertically until base level for erosion is reached

• Lateral weathering and erosion becomes dominant to etch base of limestones

Caves

• Underground solutional openings through which subsurface water circulates

• Wet or dry depends on whether it is below or above water table

Formation

• When groundwater moves through limestone along joints and bedding planes and dissolves the rock, causing cracks and fissures to develop into large cavaties

Speleothem

• Stalactites → ceiling

• Stalagmites → ground

• Stalagmites are thicker and more irregular because of splash effect

Formation

• Water from solution of limestone contains high concentrations of dissolved limestone, CO2 leaves the water and diffuses into cave atmosphere due to concentration difference, water is supersaturated with calcite and crystallises on rock surface of cave

Factors influencing formation of Karsts

1. Climate (high temp and high precip)

2. Geology (limestone, low porosity and high perviousness, bedding planes and lines of weaknesses)

3. Human activities (CC, acid rain)

4. Tectonic Hazards (mass movements)

5. Depth of water table (low WT → gentler gradient, high WT → steeper gradient)