This article focuses on the work of the Erosional landforms of groundwater.
If the rocks are permeable, thinly bedded, high jointed and cracked, then the water percolates well into it. After the water goes down to some depth vertically, the water under the ground flows horizontally within the bedding places, joints or within the materials themselves.
The downward and horizontal movement of water is the reason behind the erosion of rocks. Physical or mechanical removal of rocks by running groundwater is unimportant in developing landforms.
As a result, the work of groundwater is not seen in all types of rocks. Groundwater’s work is mostly seen in rocks like limestone or dolomites, which are has the presence of Calcium Carbonate in them.
It is by the chemical process of solution and precipitation caused by the groundwater and the surface water, the deposition develops different types of landforms.
The solution process and the precipitation process are active in the limestone and dolomites. These two processes either occur exclusively or interbedded with other rocks.
Any region of limestone or dolomitic that exhibits the landforms produced by the action of groundwater by the processes of solution and deposition is called Karst topography. This is named after the Karst region in the Balkans, which is adjacent to the Adriatic sea, developed such topography, where the region consists of limestone rocks.
Also, the Karst Topography is featured by depositional and erosional landforms.
Erosional landforms of Groundwater
Pools, Lapies, Sinkholes and Limestone Pavement, which are medium to small-sized round to sub-rounded shallow depressions are known as Swallow Holes. The Swallow holes forms on the limestone surface through the solution.
A Sinkholes are an opening which is almost circular at the top and shaped like a funnel towards the bottom with different sizes from a few square Kilometre to a size of hectares. Its depths also vary from a few metres to thirty metres or more. These Sinkholes are a common thing in Karst Areas or Limestone Areas.
These forms were formed solely by Solution action called Solution Sinks. Others might start as solution forms initially and then if the bottom of the sinkhole forms the roof of a void or cave under the ground, this might leads to collapse, that leaves a large hole opening into a cave or a void bellow called Collapse Sinks.
Sometimes, these Sinkholes are with soil mantle and look like shallow water pools and if some steps over them, it would go down similar to quicksands in deserts. The Collapse sinks are also termed Doline.
The solution sinks are more common than the collapse sinks. Sometimes the surface run-off simply runs underneath swallow and sinkholes and runs as underground streams and later it reemerges at distance as downstream from a cave opening.
Valley sinks or Uvalas
Valley Sinks or Uvalas form when the sinkholes and doline merge together due to slumping of materials (rocks) along with their margins or because of the roof collapse of caves, long-narrow to wide trenches.
Slowly, most of the surface of the limestone is eaten away by these pits and trenches that leave extremely irregular with a maze of points, grooves and ridges or lapies.
These ridges or lapies were formed due to differential solution activity along parallel to sub-parallel joints. The lapie fields will eventually turn into something like a smooth limestone pavement.
In places where there are alternating beds of rocks such as shales, sandstones, quartzites etc with limestone or dolomites in between or in the regions where the limestone is dense, massive and occurring as thick beds, caves formation are prominent.
Along the bedding planes, the water percolates through the cracks, joints, and moves horizontally. Along these bedding planes, where the limestone dissolves, long-narrow to wide gaps form and it is called Caves.
These caves can be a maze of caves at varying elevations. This cave formation at different elevations depends upon the limestone beds and intervening rocks. The cave has opened by which the streams are discharged.
The caves where the opening is present at both ends are called Tunnels.
1.how is groundwater erosion differentiated from surface water erosion?