Geomorphology for Kerala PSC: Landforms formed by Groundwater July 1, 2022
Geomorphology for Kerala PSC: Landforms formed by Groundwater
- In rocks like limestones or dolomites rich in calcium carbonate, the surface water as well as groundwater through the chemical process of solution and precipitation deposition develop varieties of landforms.
- These two processes of solution and precipitation are active in limestones or dolomites.
- Limestone or dolomitic region showing typical landforms produced by the action of groundwater
- through the processes of solution and deposition is called Karst topography.
Erosional landforms of groundwater
- Swallow holes: Small to medium sized round to sub-rounded shallow depressions called swallow holes form on the surface of limestones through solution.
- Sinkholes: A sinkhole is an opening more or less circular at the top and funnel-shaped towards the bottom.
- Doline: If the bottom of a sinkhole forms the roof of a void or cave underground, it might collapse leaving a large hole opening into a cave or a void called collapse sinks. Quite often, sinkholes are covered up with soil mantle and appear as shallow water pools. The term doline is sometimes used to refer the collapse sinks.
- Uvalas: When sink holes and dolines join together because of slumping of materials along their margins or due to roof collapse of caves, long, narrow to wide trenches called valley sinks or Uvalas form.
- Lapies: Gradually, most of the surface of the limestone is eaten away by these pits and trenches, leaving it extremely irregular with a maze of points, grooves and ridges or lapies.
- Limestone pavements: Especially, these ridges or lapies form due to differential solution activity along parallel to sub-parallel joints. The lapies field may eventually turn into smooth limestone pavements.
- Caves: In areas where there are alternating beds of rocks with limestones or dolomites in between or in areas where limestones are dense, massive and occurring as thick beds, cave formation is prominent. Water percolates down either through the materials or through cracks and joints and moves horizontally along bedding planes. The limestone dissolves and long and narrow to wide gaps called caves were formed.
- Tunnels: Caves normally have an opening through which cave streams are discharged. Caves having openings at both the ends are called tunnels.
Depositional landforms of groundwater
- Stalactites: Stalactites hang as icicles of different diameters. Normally they are broad at their bases and taper towards the free ends showing up in a variety of forms.
- Stalagmites: They rise up from the floor of the caves. In fact, stalagmites form due to dripping water from the surface or through the thin pipe, of the stalactite, immediately below it. Stalagmites may take the shape of a column, a disc, with either a smooth, rounded bulging end or a miniature crater like depression.
- Pillars: The stalagmite and stalactites eventually fuse to give rise to columns and pillars of different diameters.