Karst landscapes are shaped by the dissolution of soluble rocks, creating unique surface and subsurface features. From sinkholes and caves to complex underground water networks, these landforms result from the intricate dance between groundwater and rock.

Understanding karst is crucial for managing water resources and environmental risks. The interplay between surface and subsurface processes in karst regions highlights the interconnected nature of Earth's systems, influencing everything from local ecology to human infrastructure.

Surface Karst Landforms

Sinkholes and Depressions

• Sinkholes form closed depressions in karst landscapes through collapse of surface material into underlying voids or gradual dissolution of bedrock
  • Solution sinkholes develop from slow dissolution of exposed bedrock
  • Collapse sinkholes form suddenly when cavern roofs fail
  • Subsidence sinkholes occur gradually as loose sediment settles into voids
• Poljes create large, flat-floored depressions in karst regions, often with steep sides and internal drainage
  • Border poljes form along the boundary between karst and non-karst rocks
  • Structural poljes develop along faults or between ridges
  • Baselevel poljes occur near the water table in lowland areas
• Karst windows expose underground streams or cave passages at the surface (Mammoth Cave, Kentucky)

Exposed Rock Features

• Karren produces small-scale dissolution features on exposed limestone surfaces, ranging from millimeters to meters in size
  • Rillenkarren creates parallel grooves on steep surfaces
  • Rinnenkarren forms larger channels, often meandering
  • Kamenitzas develops shallow, pan-shaped depressions that hold water
• Tower karst (fenglin) generates isolated steep-sided limestone hills rising abruptly from flat plains (Guilin, China)
• Cone karst (fengcong) forms closely spaced conical hills with rounded tops and intervening depressions (Chocolate Hills, Philippines)

Subsurface Karst Features

Cave Formation and Types

• Caves create natural underground voids large enough for human entry, primarily through rock dissolution by groundwater
• Speleogenesis involves complex interactions between rock chemistry, hydrology, and geological structures to form caves
• Phreatic caves develop below the water table in the saturated zone
  • Characterized by rounded cross-sections and anastomosing passages
  • Form through slow, constant dissolution by groundwater (Carlsbad Caverns, New Mexico)
• Vadose caves form above the water table in the unsaturated zone
  • Typically feature canyon-like passages and vertical shafts
  • Develop through fast-moving water and gravity-driven flow (Mammoth Cave, Kentucky)

Cave Features and Hydrology

• Caverns form large underground chambers or series of chambers, often interconnected by passages
• Conduits create underground channels for water flow in karst systems, ranging from small fractures to large cave passages
• Speleothems develop as secondary mineral deposits in caves
  • Stalactites grow downward from cave ceilings
  • Stalagmites build upward from cave floors
  • Flowstones form sheet-like deposits on walls and floors
  • Helictites create twisted, gravity-defying formations
• Speleothem formation involves CO2 degassing and calcite precipitation through complex geochemical processes

Groundwater's Role in Karst

Dissolution Processes

• Groundwater acts as the primary agent of dissolution in karst systems, eroding soluble rocks through chemical and mechanical processes
• Carbonic acid forms when rainwater absorbs CO2 from the atmosphere and soil, becoming the main dissolving agent in limestone karst
  • Dissolution reaction: $CaCO3 + H2O + CO2 \rightleftharpoons Ca^{2+} + 2HCO3^-$
• Temperature, pressure, and presence of other acids (sulfuric acid) enhance the dissolution process
• Epikarst, the highly weathered zone at the top of bedrock, plays a crucial role in water infiltration and storage

Karst Hydrology

• Groundwater flow in karst aquifers combines diffuse flow through rock pores and concentrated flow through conduits and fractures
• Water table position influences karst feature development, with fluctuations leading to multi-level cave systems
• Spring discharge in karst systems can be highly variable
  • Some springs exhibit intermittent or reversing flow (estavelles)
• Karst aquifers are highly vulnerable to contamination due to rapid groundwater flow and limited filtration

Surface vs Subsurface Karst Impacts

Landscape Evolution

• Surface and subsurface karst features interconnect to form complex three-dimensional drainage networks influencing regional hydrology
• Karst landscape development creates a feedback process where surface features affect subsurface flow patterns and vice versa
• Climate, tectonics, and base level changes influence karst landscape evolution, leading to distinct regional karst styles
  • Tropical karst often features tower and cone karst (Southeast Asia)
  • Temperate karst typically develops extensive cave systems (Appalachian Mountains, USA)

Hydrological and Environmental Impacts

• Karst systems significantly impact surface water hydrology
  • Sinking streams disappear underground (Lost River, Indiana)
  • Losing rivers gradually diminish in flow along their course
  • Underground piracy alters drainage patterns
• Subsurface void collapse forms new surface features like sinkholes and collapse dolines, reshaping the landscape
• Karst landscapes exhibit high spatial variability in geomorphological and hydrological characteristics
  • Presents challenges for land use planning and water resource management
  • Requires specialized approaches for groundwater protection and sinkhole hazard mitigation