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Unit 44


Unit Overview

This unit examines karst processes and resultant landforms. The main sections are as follows:

  • Karst
  • Karst processes
  • Karst landforms and landscapes
  • Karst and caves

Water dissolves soluble rocks and minerals both at and below the surface. These processes produce many kinds of landforms. Karst refers to processes and landforms associated with the dissolution of limestone. Karst landforms and landscapes are the products of a complex set of geomorphic processes, conditions, and lithology. Water is a major control of the development of karst landscapes; without water, karst landscapes could not be formed. The three main types of karst landscapes are temperate, tropical, and Caribbean. Common karst landforms include disappearing streams, sinkholes, towers, and caves.

Unit Objectives

  • To discuss the general environmental conditions that favour the formation of karst landscapes
  • To analyze the landforms that characterize karst landscapes
  • To relate karst processes to the development of extensive underground cave systems

Glossary of Key Terms

Caribbean karst The rarest karst topography, associated with nearly flat-lying limestones; underground erosion dominated by the collapse of roofs of subsurface conduits, producing characteristic sinkhole terrain.
Cave Any substantial opening in bedrock, large enough for an adult person to enter, that leads to an interior open space.
Cockpit karst In tropical karst areas, the sharply contrasted landscape of prominent karst towers and the irregular, steep-sided depressions lying between them; cockpit refers to the depressions.
Collapse sinkhole In karst terrain, a surface hollow created by the collapse or failure of the roof or overlying material of a cave, cavern, or underground solution cavity.
Column The coalescence of a stalactite and a stalagmite that forms a continuous column from the floor to the roof of a cave.
Karst The distinctive landscape associated with the underground chemical erosion of particularly soluble limestone bedrock.
Solution sinkhole In karst terrain, a funnel-shaped surface hollow (with the shaft draining the centre) created by solution; ranges in size from a bathtub to a stadium.
Stalactite An icicle-like rock formation hanging from the roof of a cave.
Stalagmite An upward-tapering, pillar-like rock formation standing on the floor of a cave.
Temperate karst Marked by disappearing streams, jagged rock masses, solution depressions, and extensive cave networks; forms more slowly than tropical karst.
Tower In tropical karst landscapes, a cone-shaped, steep-sided hill that rises above a surface that mayor may not be pocked with solution depressions.
Tropical karst Dominated by steep-sided, vegetation-covered hill terrain; solution features are larger than in slower-forming temperate karst landscapes.
Uvala In karst terrain, a large surface depression created by the coalescence of two or more neighboring sinkholes.

Unit Outline

  • Karst
    • Associated with rock (limestone) removal by solution
    • Globally widespread
  • Karst processes
    • Karst landscape only develops where soluble limestone rich in calcite forms the stratigraphy
      • limestone poor in calcite much less soluble
      • dolomite can also form karst topography
      • more porous and permeable rock more susceptible to solution
    • The role of water: three processes contribute to erosion
      • surface streams
      • underground drainage flows
      • groundwater
      • together, these waters create karst landforms in limestone rock-water and carbon dioxide form carbonic acid, which dissolves the limestone
    • Relief
      • karst formation is inhibited in flat areas, promoted when limestone under relief
      • water erodes longer if it moves rapidly, less erosional power if moving slowly
    • Groundwater
      • occupies openings in limestone
      • water, in the form of carbonic acid, changes the calcium carbonate in limestone to calcium bicarbonate
      • karst areas often contain perched aquifers, groundwater at levels above the local water table
  • Karst landforms and landscapes (Fig. 44.6)
    • Temperate karst forms relatively slowly, contains disappearing streams, solution depressions, cave networks
    • Tropical karst develops quickly because of greater rainfall and humidity, contains steep-sided hills and larger karst features than temperate karst
    • Caribbean karst is found in Florida and Mexico in very flat areas, contains underground springs and large surface depressions
    • Disappearing streams and sinkholes
      • when a surface stream disappears it does so through a swallow hole
      • low-lying places become solution holes, and expand into solution sinkholes
      • collapse sinkholes are created when an overlying cave, cavern, or channel collapses
        • a collapse sink is the result when a rock ceiling collapses
        • a suffosion sink is the result when an unconsolidated ceiling collapses
      • an uvala is formed when two or more sinkholes coalesce, usually humid areas
    • Karst towers
      • dominate tropical karst areas; cone-shaped, steep-sided hills
        • cockpit karst in tropical areas-alternating towers and depressions
        • towers are remains of thick bedrock
        • Karst and caves
    • A cave must be large enough for an adult person to enter (any substantial opening leading to an interior open space)
    • Fully developed cave has several features
      • entrance (portal)
      • one or more chambers
      • passages
      • terminations (a place beyond which a person cannot crawl further)
    • Caves have many forms
      • linear
      • sinuous
      • angulate
    • Dripping water saturated with calcium carbonate forms precipitates with calcite in the form of travertine, produces many features on cavern ceilings
      • stalactites
      • stalagmites
      • columns
    • Cave networks
    • many unmapped networks under water

Review Questions

  1. Compare and contrast a stalactite and a stalagmite.
  2. What is cockpit karst and how does it form?
  3. List some of the surface and underground features of temperate karst, using Fig. 44.6 as a guide.