Erosional landforms created by groundwater, particularly in karst regions, result from the chemical weathering and physical erosion of soluble rocks such as limestone, dolomite, and gypsum. These processes lead to the formation of various unique and fascinating features.
1. Pools (Scallops and Flutes)
Characteristics:
- Formation: Pools, also known as scallops or flutes, are small, shallow depressions in limestone bedrock formed by the erosive action of flowing water. The water, often slightly acidic, dissolves the limestone, creating smooth, rounded depressions.
- Location: Typically found in the beds of streams or rivers in karst regions.
Examples:
- India: The limestone pools in the Meghalaya region, created by flowing streams.
- World: The pools in the karst regions of the Dinaric Alps in Slovenia, where river water flows over limestone.
2. Sinkholes (Dolines)
Characteristics:
- Formation: Sinkholes, also known as dolines, are depressions or holes in the ground caused by the collapse of a surface layer into an underground void. This occurs when groundwater dissolves the underlying soluble rock, creating voids and cavities that eventually collapse.
- Types: There are solution sinkholes (formed by the gradual dissolution of rock) and collapse sinkholes (formed by the sudden collapse of an underground cavity).
Examples:
- India: The Umpherston Sinkhole in Meghalaya.
- World: The Great Blue Hole in Belize, an underwater sinkhole formed by the collapse of a limestone cave system.
3. Lapis (Lapies or Karren)
Characteristics:
- Formation: Lapis, also known as lapies or karren, are grooves or ridges formed on limestone surfaces by the chemical weathering action of rainwater. These features are created by the dissolution of limestone along joints and bedding planes.
- Features: They can appear as sharp ridges, grooves, or elongated depressions on the limestone surface.
Examples:
- India: Lapis formations in the limestone regions of Meghalaya.
- World: The karren fields in the Northern Calcareous Alps of Austria, showcasing extensive lapies.
4. Limestone Pavements
Characteristics:
- Formation: Limestone pavements are flat, exposed surfaces of limestone that have been weathered and eroded to create a distinctive pattern of clints (blocks) and grikes (fissures). They form when the overlying soil is removed, exposing the limestone to weathering processes.
- Features: The pavement is characterized by a checkerboard appearance due to the network of cracks and joints widened by dissolution.
Examples:
- India: Limestone pavements in the Vindhya Range.
- World: The limestone pavements of the Burren in County Clare, Ireland, are one of the most extensive examples in the world.
5. Caves and Caverns
Characteristics:
- Formation: Caves and caverns are formed by the dissolution of soluble rocks by acidic groundwater. Rainwater, containing dissolved carbon dioxide, forms weak carbonic acid, which reacts with limestone, creating voids and enlarging fissures over time.
- Features: These underground voids often contain stalactites (hanging from the ceiling), stalagmites (rising from the floor), columns, and other speleothems formed by mineral deposition.
Examples:
- India: The Borra Caves in Andhra Pradesh, which feature impressive stalactites and stalagmites.
- World: Mammoth Cave in Kentucky, USA, is the world’s longest cave system, formed in limestone.
Detailed Examination with Examples
1. Pools (Scallops and Flutes)
- Meghalaya, India: Small pools formed in limestone by the erosive action of flowing water in streams and rivers.
- Dinaric Alps, Slovenia: Flutes formed on limestone bedrock by water flow, showcasing small, rounded depressions.
2. Sinkholes (Dolines)
- Umpherston Sinkhole, India: A large sinkhole in Meghalaya formed by the dissolution of limestone.
- Great Blue Hole, Belize: A giant marine sinkhole formed by the collapse of a limestone cave system during the last glacial period.
3. Lapis (Lapies or Karren)
- Meghalaya, India: Lapis formations created by the dissolution of limestone along natural joints.
- Northern Calcareous Alps, Austria: Extensive karren fields with sharp ridges and grooves formed on the limestone surface.
4. Limestone Pavements
- Vindhya Range, India: Exposed limestone surfaces showing clints and grikes.
- Burren, Ireland: Famous for its expansive limestone pavements, with a distinctive pattern of blocks and fissures.
5. Caves and Caverns
- Borra Caves, India: Limestone caves featuring speleothems formed by groundwater dissolution.
- Mammoth Cave, USA: The world’s longest cave system, with extensive underground passages and formations.
Conclusion
Erosional landforms created by groundwater, such as pools, sinkholes, lapis, limestone pavements, and caves, are key features of karst landscapes. These landforms are the result of the chemical weathering and physical erosion of soluble rocks by slightly acidic groundwater. Examples from India, like the Borra Caves and Umpherston Sinkhole, and from around the world, such as Mammoth Cave in the USA and the Great Blue Hole in Belize, illustrate the diversity and complexity of these fascinating geological features.
