Karst Processes and Landforms

South China

Karst landforms are produced by weathering and erosion in regions of carbonate rocks and evaporites. The processes involved are collectively described as karstification, and happened mainly below the ground surface.

Karst found mostly in limestone (rock with at least 50% carbonate minerals), depends on:

1) permeability & porosity

2) secondary porosity along fractures, joints, faults, etc

3) bedding thickness

4) available relief

Surficial Landforms

1) Closed depressions - dolines/sinks/sinkholes; solutional collapse: uvalas & poljes:

2) Karst valleys - allogenic valleys; blind valley; pocket valley; dry valleys

3) Minor solution features: karren

Surficial Landforms

1) Closed depressions - dolines/sinks/sinkholes; solutional collapse: uvalas & poljes

Doline: A general term for a closed depression in an area of karst

topography that is formed either by solution of the surficial limestone or by collapse of underlying caves.

Surficial Landforms

1) Closed depressions - dolines/sinks/sinkholes; solutional collapse: uvalas & poljes

Doline: A general term for a closed depression in an area of karst

topography that is formed either by solution of the surficial limestone or by collapse of underlying caves.

Surficial Landforms

1) Closed depressions - dolines/sinks/sinkholes; solutional collapse: uvalas & poljes

Doline

Surficial Landforms

1) Closed depressions - dolines/sinks/sinkholes; solutional collapse: uvalas & poljes

Doline

Surficial Landforms

1) Closed depressions - dolines/sinks/sinkholes; solutional collapse: uvalas & poljes

An uvala is a collection of multiple smaller individual sinkholes that

coalesce into a compound sinkhole. These landforms are often shallow and irregular in their overall shape, due to the merging of smaller sinkholes.

Surficial Landforms

1) Closed depressions - dolines/sinks/sinkholes; solutional collapse: uvalas & poljes

A poljes is an elongated basin having a flat floor and steep walls, formed

the coalescence of several sinkholes

Surficial Landforms

2) Karst valleys - allogenic valleys; pocket valley; dry valleys

Allogenic valley is a karst valley incised by a watercourse originating on impervious rock with a volume sufficient for it to traverse a limestone area on the surface. The valley is incised from the limestone contact and with the passage of time the river is increasingly likely to pass underground as the waters enlarge joints.

Surficial Landforms

2) Karst valleys - allogenic valleys; blind valley; dry valleys

Blind valley is a deep, narrow, flat bottomed valley with an abrupt ending. Such valleys arise in karst landscapes, where a layer of permeable rock lies above an impermeable substrate. They are created by a stream flowing within the permeable rock and eroding it from within, until the rock above collapses opening up a steep narrow valley which is then further eroded by the stream running across the impermeable valley floor.

Surficial Landforms

2) Karst valleys - allogenic valleys; blind valley; dry valleys

Dry valley is a valley found in no longer has a surface flow of water because the water sinks through the limestone and flows underground in caverns .

Surficial Landforms

3) Minor solution features:

Karren are minor forms of karst due to solution of rock on its surface.

Subsurface Features/Landforms Caves form by the dissolution of limestone. Rainwater picks up carbon dioxide from the air, and more especially from the soil (where micro-organisms and the decay of organic matter generate high levels of carbon dioxide), combining to form carbonic acid. As this acidic water percolates through the limestone, it gradually enlarges the bedding planes, joints and fissures within the rock, eventually creating caves.

Underground water flow Water flowing though the limestone will follow the line of least resistance, which generally means along bedding planes, joints and fault lines. Over time, the water generally enlarges the major joints and bedding planes within the rock to form a cave. Local geology has an important role to play in determining the style and type of cave formed.

Phreatic: below groundwater table (saturated).

Vadose zone): surface to top of groundwater (Unsaturated).

Cave Deposits Once cave has been formed, it may become partially or totally infilled with cave deposits. Two major types of deposit are stalactites and stalagmites (speleothems).

Once percolating water reaches the underlying cave atmosphere, which has generally lower levels of carbon dioxide, it degasses and by doing so, becomes supersaturated with calcium carbonate, which is deposited as speleothem. A variety of different types of speleothem can develop, but the majority are composed of calcite. Near the entrances to many caves, evaporation of the drip waters can enhance stalagmite deposition, which is why many of the caves are almost choked by calcite near their entrances.

Cave Deposits Once cave has been formed, it may become partially or totally infilled with cave deposits. Two major types of deposit are stalactites and stalagmites (speleothems).

Once percolating water reaches the underlying cave atmosphere, which has generally lower levels of carbon dioxide, it degasses and by doing so, becomes supersaturated with calcium carbonate, which is deposited as speleothem. A variety of different types of speleothem can develop, but the majority are composed of calcite. Near the entrances to many caves, evaporation of the drip waters can enhance stalagmite deposition, which is why many of the caves are almost choked by calcite near their entrances.

Cave sediments Many caves have thick deposits of a coarse gravels, or thick deposits of silt and laminated clays, with climate having a big effect on the amount of sediment in transport. In todays warm, wet interglacial climates, hillsides are often rapidly eroding, washing much sediment that makes its way into cave systems.

Speleothem 18O records

The relative age of a cave deposits sometimes measured by palaeomagnetic analysis. Through time, the Earths magnetic north pole has wandered around by several degrees, periodically flipping from north to south and back again. These fluctuations in the magnetic field have been independently dated using other methods. The last time the magnetic pole reversed was 780,000 years ago, and before that, about 910,000 years ago. These changes in the Earths magnetic field are recorded in the sediments found throughout the caves.

Clay particles deposited in still water will preferentially align themselves to the prevailing magnetic field at the time of deposition. Thus by taking carefully oriented cores of fine grained, clay rich sediment, it is possible using a magnetometer to determine the direction (and thus polarity) of the magnetic pole when the sediment was deposited. The most recent sediments will be aligned towards the current North Pole, whereas older sediments preserve will preserve evidence of former pole positions.

Tower karst

Tropical Karst all temperate landforms are present, but the landscape is dominated by

residual hills rather than the closed depressions of temperate karst higher temperature, total precipitation, & precipitation intensity produce

rapid & prolonged corrosion rapid plant growth & decay combine with extreme microbial activity to

supercharge infiltrating water with CO2 and intensify the solution process cone karst, tower karst, phytokarst

Tropical Karst Cone karst or kegelkarst (conical hill karst), this is a landscape

of star-shaped hollows surrounded by steep, rounded hills, and found in tropical karst country. The cockpits, now floored with alluvium, are the hollows, or dolines, formed by the solution of limestone. They can be 100m deep and usually contain a streamsink. The classic area of cockpit karst is found in Jamaica.

Tropical Karst Cone karst or kegelkarst

Tropical Karst Cone karst Tower karst are steep or vertical sided limestone towers each 30-300 m

high. Towers originate as residual cones and are then steepened by water table undercutting from surround alluviated plains.

By far the most extensive and best developed tower karst is the Guangxi province of southern China Many towers are riddled with relict caves at high levels, and with active caves through their bases.

Tropical Karst Cone karst Tower karst

Tropical Karst Cone karst Cockpits Tower karst Phytokarst a type of small scale solutional sculpturing or karren which

forms with the assistance of certain algae and other micro-organisms. Filamentous algae bore their way into limestone to produce black-coated, jagged pinnacles marked by delicate, lacy dissection that lacks any gravitational orientation.

Cave management (or mismanagment)