Q.Underground flow of water is more common than surface run-off in limestone areas. Why?

Limestone, primarily composed of calcium carbonate, is highly susceptible to dissolution by rainwater, which becomes slightly acidic as it absorbs carbon dioxide from the atmosphere. This chemical weathering process enlarges existing cracks, fissures, and joints within the rock, creating numerous pathways for water to penetrate.

Instead of flowing over the surface, water readily infiltrates these widened openings and percolates underground. Over extended periods, this continuous dissolution forms extensive subterranean drainage systems, including caves, sinkholes, and underground rivers, which are characteristic features of karst topography. This high permeability and solubility of limestone mean that most precipitation quickly moves into the subsurfa …

Limestone landscapes exhibit a unique hydrological characteristic: water predominantly flows underground rather than as surface runoff. This phenomenon is directly attributable to the specific chemical composition and physical properties of limestone, which lead to the formation of what is known as Karst topography.

Limestone is a sedimentary rock primarily composed of calcium carbonate (CaCO₃). While seemingly solid, this rock has a crucial chemical property: it is soluble in weak acids. Rainwater, as it falls through the atmosphere, absorbs carbon dioxide (CO₂), forming a dilute carbonic acid (H₂CO₃). When this slightly acidic rainwater comes into contact with limestone, a chemical reaction occurs where the calcium carbonate dissolves.

Initially, rainwater infiltrates the limestone through existing natural cracks, joints, and fissures. These openings, though small at first, provide pathways for the water to penetrate beneath the surface. As the acidic water flows through these pathways, it continuously dissolves the surrounding limestone. Over long periods, this dissolution process progressively enlarges the cracks and fissures, transforming them into wider conduits, channels, and eventually vast underground cave systems.

This continuous enlargement of subsurface pathways means that water finds it easier to move underground than to flow across the surface. Surface streams in limestone regions often "disappear" abruptly into sinkholes or swallow holes, which are depressions formed by the collapse of overlying rock into an underground cavity. These disappearing streams then become part of the subterranean drainage network. …