Sub-topic 7: Karst Topography and its Landforms
Karst topography refers to a landscape formed from the dissolution of soluble rocks such as limestone, dolomite, and gypsum. This process, known as karstification, leads to unique surface and subsurface features. Understanding karst is crucial for comprehending various geological processes and their impact on human activities.
The Karstification Process
The primary agent of karstification is slightly acidic rainwater. Carbon dioxide from the atmosphere and soil dissolves in water to form carbonic acid (H₂CO₃). When this acidic water percolates through soluble rocks like limestone (calcium carbonate, CaCO₃), it reacts and dissolves the rock, creating voids and channels.
Dissolution of soluble rocks by slightly acidic water (karstification).
The chemical reaction is as follows: CaCO₃ (limestone) + H₂CO₃ (carbonic acid) → Ca(HCO₃)₂ (calcium bicarbonate, soluble)
Surface Karst Features
Karst landscapes are characterized by a variety of distinctive surface features, often formed by the collapse of underlying caves or the dissolution of rock at the surface.
Dolines are common surface depressions in karst regions.
Dolines, also known as sinkholes, are bowl-shaped or cylindrical depressions formed by the dissolution of rock or the collapse of cave roofs. They can vary in size from a few meters to hundreds of meters in diameter.
Dolines are a hallmark of karst topography. They can form in several ways: dissolution dolines form gradually as surface water dissolves bedrock; subsidence dolines form when the roof of an underground cavity collapses; and collapse dolines are the result of a sudden collapse of the surface into an existing underground void. Their presence indicates active dissolution and subsurface drainage.
Uvalas are larger depressions formed by the merging of dolines.
Uvalas are larger, irregular depressions that result from the coalescence of several dolines. They often have a more complex shape than individual dolines.
As karst processes continue, adjacent dolines can expand and merge, forming larger, compound depressions known as uvalas. These features can be several hundred meters across and often contain multiple smaller sinkholes within their broader expanse.
Poljes are extensive, flat-floored karst depressions.
Poljes are large, flat-bottomed depressions, often several kilometers in length, found in karst regions. They are typically drained by swallow holes or underground streams.
Poljes represent the most extensive surface karst features. They are formed by a combination of dissolution and collapse, often along structural weaknesses in the bedrock. Their flat floors are usually covered with alluvial deposits, and they may be seasonally flooded, with water disappearing into swallow holes.
Karren are fluted or grooved rock surfaces.
Karren, also known as clints and grikes, are small-scale surface features characterized by grooves, channels, and pits etched into the rock surface by dissolution.
Karren are formed by the dissolution of limestone at the surface, creating a corrugated or pitted landscape. These features can range from shallow grooves to deep, steep-sided channels, often referred to as grikes, with the remaining raised blocks called clints. They are a testament to the fine-scale erosional power of karst processes.
Subsurface Karst Features
Beneath the surface, karst landscapes host a complex network of caves and associated formations.
Caves are underground voids formed by dissolution.
Caves are natural underground chambers or series of chambers formed by the dissolution of soluble rocks. They are the most iconic features of karst topography.
Caves are the result of water percolating through joints and bedding planes in soluble rocks, widening them over time. They can develop into extensive systems with multiple levels, passages, and chambers. The formation and evolution of caves are directly linked to the hydrological regime of the area.
Speleothems are mineral deposits formed in caves, primarily from the precipitation of calcium carbonate. Common examples include stalactites (hanging from the ceiling) and stalagmites (rising from the floor). These formations grow very slowly, drop by drop, as mineral-rich water evaporates or loses dissolved carbon dioxide. The intricate shapes and formations within caves are a direct result of the slow, continuous process of dissolution and deposition.
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Stalactites and stalagmites are common cave formations.
Stalactites hang from cave ceilings, while stalagmites rise from cave floors, both formed by mineral deposition from dripping water.
Stalactites are icicle-like formations that grow downwards from the roof of a cave, typically formed by the deposition of calcium carbonate as water drips. Stalagmites are similar formations that grow upwards from the cave floor, often formed by the splash of water from a stalactite. When a stalactite and stalagmite meet, they form a column.
Underground rivers and streams are integral to karst hydrology.
Water in karst regions often flows underground through a network of caves and conduits, disappearing at the surface via swallow holes.
Surface streams in karst areas frequently disappear underground into sinkholes or swallow holes, becoming subterranean rivers. These underground drainage systems are highly efficient but can be vulnerable to pollution. The flow paths are often complex and can change over time.
Swallow holes are natural pits or holes in the ground that carry surface water underground.
Significance and Challenges of Karst Topography
Karst landscapes present unique opportunities and challenges for human settlement and development. Their porous nature affects water availability and quality, and the presence of underground voids can pose engineering challenges.
| Feature | Formation Process | Typical Location |
|---|---|---|
| Doline | Dissolution or collapse | Surface depressions |
| Uvala | Merger of dolines | Larger surface depressions |
| Polje | Extensive dissolution and collapse | Large, flat-floored depressions |
| Karren | Surface dissolution | Grooved rock surfaces |
| Cave | Subsurface dissolution | Underground chambers |
| Stalactite/Stalagmite | Mineral deposition | Cave ceilings/floors |
A uvala is a larger, more irregular depression formed by the merging of multiple dolines.
Learning Resources
Provides a foundational understanding of karst landscapes, their formation, and key features with illustrative examples.
An overview from the U.S. Geological Survey explaining the processes and features of karst topography, including its impact on water resources.
A practical guide from the University of Kentucky detailing karst features and their implications for land management and water quality.
A more in-depth look at the hydrological and geomorphological processes governing karst systems, suitable for advanced learners.
A visual tutorial explaining the chemical and physical processes that create karst landscapes and their characteristic landforms.
Details on how caves form and the various types of speleothems (stalactites, stalagmites) found within them, from the National Park Service.
A comprehensive encyclopedia entry covering the definition, formation, and global distribution of karst landscapes.
An informative article explaining sinkholes, their causes, and the broader context of karst topography with clear images.
A lecture segment focusing on the geomorphological processes of karstification and the development of karst landforms.
Explores the critical relationship between karst topography and groundwater systems, highlighting challenges in water management.