GLS210 Karst

Lindley Hanson, Department of Geological Sciences, Salem State College

[Geomorphology][Province Geology][GeoIndex]

Readings:

• Bloom: Chapters 8
• Jones: Chapter 9: Groundwater
• GFS: Karst Landforms and Lakes
  
  ****Karst Link Page maintained by the he Association of Polish Geomorphologists
  Weathering and Karst Bob Newton
  Cave database Searchable database compiled by Eric Madelaine
  Karst in British Columbia
  Cave Page: Australian Caves
  Karst
  The Virtual Cave

Introduction

• Definition of karst:
  • Terrain with distinctive characteristics of relief and drainage arising primarily from the solution of soluble bedrock by natural waters. Features of karst terrains may include a variety of sinkholes, solution valleys, caverns, towers and cones, etc.
•  Terms:
  • Corrosion: chemical erosion or a rock
  • Corrasion: mechanical erosion of rock by a moving agent (e.g water, ice, etc.)
  • Glossary of Karst related terms by Arthur Clarke
  • Cave and Karst Terminology by J.N. Jennings

How Karst is formed

CONDITIONS contributing to the maximum development of karst

• Soluble rock at or near the surface (Ca Carbonate, rock salt, gypsum, etc.)
• Dense rock (little interstitial porosity) which is highly jointed. Chalk develops poor karst due to high porosity.
•  High hydraulic gradient produced by steep topography or entrenched rivers. Moving water corrodes much faster than standing water.
  • High hydraulic gradient reduces the residence time thereby inhibiting the development of equilibrium between the rock and and surrounding waters
•  high rainfall
•  high biological activity
  •  humus:
    • increases the acidity of the water
    • increases partial pressure of CO2 and releases organic acids
  •  Algae: produces phytokarst (an intricately pitted, sharp-edges topography formed by the solution of limestones by acid solvents generated by algae)
  •  Organic waste: Phosphate-rich guano produced by birds and bats strongly corrode limestone.
  • (Rock phosphate produced by the reaction of guano and limestone fills karst cavities, in some cases to a depth of 20 m. producing commercial deposits.)
•  Temperature 
  • High temperature: Increases biochemical activity so that more CO2 and organic acids are formed
  • Low temperature: Cold water has a higher potential to become more acid
  • Example: 10°C water dissolves 2x more CO2 than 30° water
  • 0°C water dissolves 3x more CO2 than 30° water
  • However, in cold regions there is much less CO2 available to dissolve in water because of the low biochemical activity. In permafrost regions the water is frozen. Acid water is concentrated in the active layer and is only.
•  Pressure:
  • Water under pressure can dissolve more CO2 and therefore hold more CaCO3 in solution
  •  Release of pressure will result in deposition of CaCO3 from water previously under hydraulic pressure (e.g. travertine)
  • Turbulence may also result in deposition (e.g.tufa deposits in rivers)
•  Mixing of carbonate waters
  • Because of the nonlinear relationship between Ca++ and CO2 (handout), an under saturated, aggressive body of water is produced by the mixing of two saturated water bodies. 

Climate and karst

• Polar Regions: Karst is poorly developed
  • Reasons:
    • 1. Low rainfall and short runoff season
    • 2. Limited infiltration in permafrost regions
    • 3. Cold temperatures result in low biochemical activity.
    • Even though ground water may have large amounts of CO2 it is not particularly aggressive. Why?
•  Cold Humid Mid Latitudes: Well developed karst characterized by limestone sinks and closed depressions
  • Reasons:
    • 1. Greater precipitation
    • 2. Infiltration is uninhibited
    • 3. Greater biochemical activity
      • a. More CO2
      • b. more organic acids
    • Karst in the US: Show Karst: Clickable image of US with caves
      • Missouri Ozarks,
      • Indiana,
      • Woodville Karst Plain (part of the Gulf Coastal Lowland physiographic region) stretches from the southern edge of Tallahassee, Florida, tothe Gulf of Mexico.
      • Mammoth Cave, Kentucky
      • Cave Tours: Jewel Cave, SD and Lechuguilla Cave, NM
        
•  Subhumid and semiarid steppe and savanna grasslands: Little to no karst development
  • Reasons:
    • Very low precipitation
    • During hot dry seasons groundwater tends to move upward and deposit carbonate rather than dissolve it. (Caliche/duricrust: hard crust on arid soils formed by the precipitation of CaCO3 ) 
  • **Limestone in arid regions forms ridges and cliffs rivaling sandstone in its stability.
•  Tropical Rainforests: Well developed karst characterized by residual hills. Region where karst is best developed.
  • Reasons:
    • Very high rainfall
    • Warm temperatures and thick vegetation results in high concentration (partial pressure) of organic acids and CO2
    • Groundwater flows through the ground in large quantities and is very aggressive
• Other controlloing factors:
  • Besides climate and lithology, other factors which strongly influence the nature of karst landscapes are:
  •  
    • Base-level fluctuations: caused by tectonic activity or changes in sea level
    • (i.e. eustatic lowering during glaciation)
    •  Structure: solution exploits fracture systems and other planes of weakness that are structurally controlled
    • Stratigraphy: thickness of limestone and permeability of adjacent units
    • Geologic history (is the landscape active, relict, or exhumed?)
    •  Time

Karst Features 

• Microforms (See Summerfield Table 6.6 p. 149)
  • Karst Drainage: Most drainage is subterranean with very few continuous surface streams. Surface drainage patterns tend to be CENTRIPETAL.
    • Unlike most fluvial terrains, which are progressively eroded downward towards baselevel, karst terrains are eroded
      • upward by subsurface abstraction into subterranean drainages and
      • by lateral planation by streams already adjusted to base level.
•  Dolines ( sinkholes; closed depressions)
  • solution doline: Funnel-shaped doline formed by solution along a joint or along the intersection of several joints. Regolith drapes the floor of the doline.
  •  collapsed doline: Steep-sided doline formed by subterranean corrosion. Large cave forms, overlying rock no longer is supported and collapses.
  •  Subsidence doline: Similar to solution doline but overlying soil has washed into the cave system.
  •  Swallow hole (ponors): Limestone sink into which a stream disappears.
  •  Subjacent karst collapse dolines: Overlying non-carbonate rock collapsed into a limestone cavern
•  Factors conducive to sinkhole formation:
  • flat land: doline formation is inversely proportional to slope as a result of lower infiltration rates and greater runoff rates.
  • Massive well-jointed limestone
  • cRich vegetative cover 
• Uvaluas (Compound sinkholes): Consist of a series of intersecting dolines
•  Karst valleys
  • Blind valley: Well developed valley lacking a stream. Part of an intricate drainage system which is also dry.
  •  Allogenic Valley (formed or originating elsewhere): Deep gorge-like valley formed as a stream flows from a nonkarstic region into a karstic region.
  •  Dry valley: Well developed valley lacking a stream. Commonly part of an intricate drainage systems which is also dry. Forms when a surface-water drainage system becomes diverted underground.
    • Theories on the formation of dry valleys:
    •  Superposition theory
      • Drainage system develops on less permeable rock overlying limestone
      • Drainage system is superimposed on limestone terrane
      • Subterranean drainage forms and valley becomes dry
    •  Base level change
      • Drainage developed with groundwater table close to surface
      • Uplift, lowering of sea level, or local base level by erosion results in lowering of gw table and subterranean migration of surface water 
  • Pocket valley: Valley headed by a large spring
  •  Poljes: Large valleys or depressions with broad valley floors which are oriented along a tectonic trend.
  • Genetic sequence might be: doline--uvala--poljes?
• "Tropical" Karst: Contains all the features above plus the features described below:
  • Polygonal karst (cockpit karst): Egg-carton-type topography developed by extensive solution along intersecting joints
  •  Cones, mogotes, & towers: Isolated carbonate hills on a alluvial plain. The plain is either on impermeable bedrock rock or on limestone that has been lowered close to base level.
    
  • Physical Geology Tour of Karst features 

Bloom, Arthur. 1998, Geomorphology, A systematic analysis of Late Cenozoic landforms, (3rd edition): Prentice Hall, Upper Saddle River, N.J., 482 p.

Chorley, R.J., Schumm, S.A., Sugden, D.E., 1984, Geomorphology: Methuen and Co. Ltd., London, 605 p.

*Jennings, J.N., 1971, Karst: MIT Press, Cambridge, MA, 252 p.

Ritter, D.F., Kochel, C.R., and Miller, J.R., Process Geomorphology (3rd Edition): Wm.C. Brown Publishers, Dubuque, IA, 544 p.

Summerfield, M.A., 1991, Global Geomorphology: John Wiley and Sons, New York, NY, 536 p.

*Trudgill, S., 1985, Limestone geomorphology: Longman, London, 196 p.

 

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