Groundwater is a significant geomorphological agent. It seeps through cracks in the rocks and moves slowly, pulled deeper and deeper by gravity. If the rock is permeable, such as sandstone, water will easily pass through it. Although the amount of subsurface water varies from location to place, it has a significant effect on forming the earth's surface features. Its work is mostly limited to subsurface locations, yet it does play a significant role on the surface as well. In this article, we will discuss Groundwater as a Geomorphological Agent which will be helpful for UPSC/IAS exam.

How Does Groundwater Act as a Geomorphological Agent?

• The water which percolates inside the earth is called underground water.
• As it rains, rainwater collects carbon dioxide (CO₂).
• Carbonic acid is formed when CO₂ reacts with water (CO₂ + H₂O ⇌ H₂CO₃).
• The slightly acidic water seeps into the earth and travels through soil pore spaces, cracks, and fractures.
• There are two sorts of topographical landforms formed by subsurface water working on limestone.
  • Surface topographical features such as sinkholes and swallow holes.
  • Underground topographical features such as caverns, stalactites, and stalagmites.

Erosional Landforms Formed Due to Groundwater

Sinkholes

• A sinkhole is a depression in the ground caused by limestone or chalk region erosion.
• It is a circular or funnel-shaped opening at the top and funnel-shaped at the bottom.
• They form where the limestone is more prone to the solution, weathering, or where an underground cover near the surface has collapsed.
• These holes are formed by the widening of fissures occurring in such rocks as a result of rainwater's continual solvent action.
• A solution sink is a sinkhole that has formed purely via the process of solution.
• Some sinkholes are steep-sided dug holes filled with earth washed down from nearby hillsides.

Swallow Holes

• They are cylindrical in shape and are found at a depth beneath the sinkholes.
• Surface streams frequently enter sinkholes in limestone environments and then disappear underground through swallow holes because these openings are connected to the subsurface caverns on the other side.
• Following are some examples of sinkholes/swallow holes:
  • Blackhole - Seawater
  • Blue Hole - Deep underwater
  • Cenotes - Belize (British Honduras)
  • Sotanos - Mexico
  • Tomo - New Zealand

Doline

• In karst regions, a doline is a closed depression that drains underground.
• It might be formed like a cylinder, a cone, a bowl, or a dish.
• The diameter varies greatly, from a few meters to hundreds of meters.
• Doline is derived from the Slovenian term Dolina, which means valley.

Karst Window / Fenster

• A geomorphic feature generated by the dissolving of carbonate bedrock is known as a Karst Fenster.
• A spring rises from this feature, and the discharge disappears into a sinkhole.
• A Karst Fenster is formed when segments of a subterranean stream's roof cave in, exposing some of the subsurface streams to the surface.
• A Karst window is formed when many adjacent sinkholes collapse and form an open, broad space.

Lappies/Karren

• Lappies are uneven grooves and ridges that occur after the majority of the surface of the limestone is removed by the solution process.
• The most widespread surface karst landforms are small solution pits, grooves, and runnels, collectively called Karren.

Uvala

• Uvalas are karst depressions that are significantly larger than sinkholes, with smoother slopes and more interesting three-dimensional formations.
• Collection of multiple smaller individual sinkholes that coalesce into a compound sinkhole.
• A single uvala usually contains a number of sinkholes.

Polje

• The Polje basin is a long, narrow basin with a level bottom and steep cliffs. It is the result of the merging of many sinkholes.
• The basins are typically 250 square kilometers in size and might show "disappearing streams."
• The majority of these basins have steep enclosing walls that range in height from 50 to 100 meters, earning the term "blind valley."

Caves

• Cave streams are generally discharged through an aperture in the cave.
• Tunnels are caves that have an aperture on both ends.
• The dissolution process produces a distinctive landform known as karst, characterized by sinkholes and underground drainage.
• Cave formation is common in locations with alternating beds of rocks (shales, sandstones, quartzites) with limestones or dolomites in between, or where limestones are dense, massive, and occur as thick beds.
• Limestone caves are often adorned with calcium carbonate formations produced through slow precipitation.
• These include flowstones, stalactites, stalagmites, helictites, soda straws, and columns.

Depositional Landforms Due to Groundwater

Curtains/Drapes

• Rainwater drips from a cave roof's lengthy fracture, forming a continuous strip of calcites.
• Numerous needle-shaped dripstones hanging from the cave ceiling are called Drapes or Curtains.

Stalactite

• Water drops containing dissolved limestone trickle down via cave roof fractures.
• Water drops expel carbon dioxide and deposit calcite.
• Calcite pillars hang from the cave's roof as calcite deposits accumulate over time.
• Usually, the base is broader than the free end of the hanging stalactites.
• It's known as stalactite, and it's known as helictites when the stalactite stretches to the sidewalls.

Stalagmite

• Stalagmite is the formation of calcite icicles that rise upward from the cave floor.
• Stalactites are calcium carbonate deposits that hang like icicles from the ceiling.
• Whereas stalagmites are calcium carbonate deposits that rise from the ground.
• Halagmites are those that stretch horizontally or diagonally from stalagmites.

Pillar

• A pillar is formed when both a stalagmite and a stalactite connect together.
• The diameter of the pillar varies.

Conclusion

Like surface water, underground water is a grading agent. It also performs erosion, transportation, and deposition, resulting in the production of a variety of beautiful topographical characteristics. Groundwater's work is not visible in all types of rocks. The work of groundwater is best visible in rocks containing calcium carbonates, such as limestone or dolomites. The deposition of different types of landforms is induced by the chemical process of solution and precipitation caused by groundwater and surface water.