How Groundwater Moves Through the Earth’s Surface

• Surface water percolates into the ground when:
  • The rocks are permeable (allow water to pass through).
  • The rock layers are thinly bedded (arranged in layers).
  • The rocks are highly jointed or cracked.
• Once water seeps vertically down:
  • It moves horizontally along bedding planes, joints, or pores in the rock.
  • This horizontal and vertical movement enables chemical weathering and erosion of soluble rocks like limestone.

Nature of Groundwater Erosion

• Mechanical (physical) erosion by groundwater is minimal or insignificant.
• The dominant form of erosion is chemical, mainly through:
  • Solution – Dissolving soluble minerals like calcium carbonate.
  • Precipitation – Re-depositing the dissolved material under certain conditions.
• These processes are particularly effective in rocks like:
  • Limestone
  • Dolomite
  • Which are rich in calcium carbonate (CaCO₃)

Karst Topography

• Landforms developed due to the chemical action of groundwater in limestone or dolomite regions are collectively known as Karst Topography.
• The name originates from the Karst region in the Balkans, near the Adriatic Sea.
• Karst topography is known for:
  • Distinctive surface and underground landforms
  • Created by the processes of solution and deposition
  • Found where limestone or dolomite is present either exclusively or along with other rock types

Erosional Landforms Created by Groundwater

a) Swallow Holes (Solution Holes)

• These are shallow, round or sub-rounded depressions formed on the limestone surface.
• Created by the chemical solution of calcium carbonate by water.
• Water enters underground through these openings.

b) Sinkholes

• Common in limestone regions.
• Appear as circular depressions at the surface, funnel-shaped towards the base.
• Size:
  • Area: Ranges from a few square meters to several hectares
  • Depth: Can be less than half a meter to over 30 meters

Types of Sinkholes:

             1. Solution Sinks:

• • • Formed entirely due to the dissolving action of water.
    • More common in nature.
    • 2. Collapse Sinks (Dolines):
    • Begin as solution sinks.
    • When the roof of an underground cave collapses, it forms a large depression.
    • These are dangerous if hidden beneath soil – stepping on them is like stepping into quicksand.
• In some cases, sinkholes may accumulate rainwater, forming shallow pools on the surface.

c) Uvalas (Valley Sinks)

• Formed when multiple sinkholes and dolines merge together.
• Causes include:
  • Collapse of cave roofs
  • Slumping or erosion of the edges of nearby sinkholes.
• Result: Creation of long, narrow to wide trenches, known as valley sinks or uvalas.

d) Lapies

• Created due to differential solution along joint lines in limestone.
• The surface becomes rugged and irregular, resembling a maze of grooves, ridges, and pits.
• This rough terrain is referred to as Lapies.
• Over time, Lapies fields may become smooth and are known as limestone pavements.

e) Limestone Pavements

• These are flat, smooth surfaces created when the rugged lapies are further weathered.
• Result from continuous solution action, which wears down surface irregularities.

Formation of Caves

a) Conditions Favoring Cave Formation

• Found in areas with:
  • Alternating layers of limestone and other rocks like shales, sandstones, quartzites.
  • Or where limestone is massive, dense, and forms thick beds.

b) Process

• Groundwater seeps through joints and cracks in the rock.
• It moves horizontally along bedding planes.
• Over time, limestone dissolves, forming long, narrow or wide cavities, known as caves.

c) Features of Caves

• Maze of caves can form at different depths, depending on:
  • Thickness of limestone
  • Arrangement of rock beds
• Many caves have entrances and exits for underground streams.
• If caves have openings at both ends, they are known as tunnels.

Depositional Landforms Inside Caves

a) Process of Deposition

• Limestone is rich in calcium carbonate (CaCO₃).
• Rainwater absorbs carbon dioxide (CO₂), forming carbonic acid.
• This acid dissolves calcium carbonate and carries it in solution.
• When the water evaporates or loses CO₂:
  • Calcium carbonate is precipitated and gets deposited inside the cave.

b) Stalactites

• Hang from the roof of caves like icicles.
• Formed when mineral-rich water drips down, depositing CaCO₃.
• Appear in various shapes, usually broad at the base, tapering downward.

c) Stalagmites

• Grow from the cave floor, formed by water droplets falling from stalactites.
• Appear as:
  • Columns
  • Discs
  • May have smooth rounded ends or crater-like tops.

d) Pillars or Columns

• When a stalactite and stalagmite meet, they fuse together.
• The resulting structure is called a pillar or column.
• These can vary in thickness and shape.