The geological action of the ground water involves processes like erosion, transportation and deposition.
Erosion
As we know, ground water circulates slowly under the influence of gravity, in general, following the slopes of the water-table. The rate of water movement is very slow and vary considerably from one place to another according to the permeability of the rocks.
Mechanical processes of erosion are absolutely insignificant in case of underground water. Ground water brings about erosion mainly through chemical processes i.e. by the solution action, which is particularly effective in regions of soluble rocks like limestone, dolomite, gypsum and anhydrite, rocksalt etc.
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The dissolving capacity of ground water depends on its content of carbon dioxide and free oxygen as it enters the zone of aeration and increases with a rise in temperature and pressure. When underground water circulates through limestone and other soluble rocks it tends to dissolve the material along the joints and bedding planes producing passages and chambers of all dimensions.
Underground water is particularly effective in the solution of limestones and produces a distinctive landscape together with underground caves. The topography thus developed is known as Karst-topography, after an area of that name in northeastern Italy and northwestern Yugoslovia, where it was first investigated in detail. Karst topographic features develop both above and under the ground surface.