karst definition by jennings (1985) “a terrain with distinctive landforms and drainage arising...

KarstDefinition by Jennings (1985)

“A terrain with distinctive landforms and drainage arising from greater rock solubility in natural water that is found elsewhere.”

Important Components of Definition

• A distinctive landform developed on highly soluble rocks.

– Most often, limestone.• 60 % CaCO3 before karst will start to

form.

• 90 % CaCO3 before well developed karst will form

– Evaporites (gypsum/halite)

– Quartzite (humid, tropics)

Important Components of Definition

• A unique drainage pattern resulting from the movement of most water into subsurface.

– Holokarst - Precipitation moves directly underground; little, if any, channelized flow.

– Fluviokarst - clear that karst landforms are superimposed on former fluvial landscape.

Calcite Dissolution

From Ritter et al. (1995)

Dissolution Reactionsfor Calcite

CO2 + H2O H2CO3

H2CO3 H+ + HCO3-

CaCO3 Ca2+ + CO3-2

CO3-2 + H+ HCO3

-

Equation 1

Equation 2

Equation 3

Equation 4

CaCO3 + H20 + CO2 Ca2+ + 2HCO3

-

Summary Equation

Controls on Solution Rates

• Degree of saturation: slow rates close to saturation. Change is non-linear.

• Fracture width– 1 to .1 mm: flow is laminar; dissolution rate

based on discharge of water through fracture.

– >5 mm: flow may be turbulent; dissolution rate based on rate of chemical reactions at surface of mineral grain.

– 1-5mm: varies with site conditions; combination of two.

• Other Factors: Pco2; temperature of water

Solution Rates

From Ritter et al. (1995)

Karst LandformsHumid, Temperature Climates

• Dolines (sinkholes): small, shallow depression; commonly wider than they are deep.– Solution Sinkhole: related to subcutaneous

zone

– Collapse Sinkhole: material fails into subsurface cavity previously created by dissolution

• Uvala: large closed depression formed by coalescence of one or more dolines.

• Karst Plain: A plain composed of closed depressions and subterranean drainage in karst region.

• Swallet (swallow hole): A place where water disappears underground in karst region. Swallet commonly used to describe loss of water in stream bed.

Solution Sinkhole Development

From Ritter et al. (1995)

Collapse Sinkhole

From Ritter et al. (1995)

Sinkhole Plain

From Ritter et al. (1995)

Blind and Dry Valleys

From Ritter et al. (1995)

Karst LandformsHumid, Temperature Climates

• Blind Valley: A valley that end abruptly where stream vanishes underground.

• Sinking Stream: stream that vanishes underground, usually at terminus of blind valley.

• Resurgence: point where waters from sinking stream reemerges from underground.

• Dry Valley: Valley that no longer exhibits channelized flow.

• Cave: A natural underground room or series of rooms large enough to be entered by a person.

Karst LandformsHumid, Tropical Climates

• Cockpit Karst: a conglomeration of closed depressions surrounded by conical hills - similar to cone karst where depression are star-shaped.

• Tower karst: Type of karst characterized by isolated, steep-walled hills separated by flat lying plain of alluvium.

Cave Shapes(Reach Scale)

From Ritter et al. (1995)

Cave Patterns

From Ritter et al. (1995)

Cave Characteristics

• Vadose Caves

– Flow always moves downward along easiest route

– Governed largely by rock structure

– Dominated by canyons and shafts

– Caves tend not to converge unless forced to by rock structure

• Phreatic Caves

– Caves may descend well below water table and then rise to level of water table

– Tend to cut across rock structure

– Dominated by elliptical tubes

– Caves tend to converge , developing along hydraulic efficient paths