Q.Limestones behave differently in humid and arid climates. Why? What is the dominant and almost exclusive geomorphic process in limestone areas and what are its results?

Limestones are made of calcium carbonate, which dissolves readily in water, especially when the water is slightly acidic. In humid climates, abundant rainfall supplies this water continuously, so chemical weathering proceeds rapidly and carves deep, distinctive landforms. In arid climates, the lack of water means this dissolution happens very slowly, so limestones there are weathered mostly by physical processes like wind abrasion and thermal expansion, leaving the rock largely intact.

The dominant and almost exclusive geomorphic process in limestone areas is solution, a form of chemical weathering where carbonic acid in rainwater reacts with calcium carbonate and carries it away in solution. This process produces a suite of landforms collectively called karst topography.

Its results include:

• Sinkholes (dolines) — collapsed depressions where the roof of an underground cavity gave way.
• Caves and caverns — large underground voids dissolved along joints and bedding planes.
• Underground drainage — streams disappear into swallow holes and flow through cave systems instead of on the surface. …

Limestone is a rock that quietly surrenders to water. Unlike granite or basalt, which resist chemical attack and mostly break down through physical forces, limestone is made largely of calcium carbonate — a mineral that reacts readily with even weakly acidic water. That single fact explains why the same rock looks so different in a rainy valley and a desert plateau.

In a humid climate, rainfall is frequent and vegetation is thick. Decaying plant matter releases carbon dioxide into the soil, and rainwater itself absorbs CO₂ from the atmosphere. The result is carbonic acid — a weak acid, but persistent. When this water seeps into cracks in the limestone, it dissolves the calcium carbonate directly. Over centuries, this chemical weathering hollows out the rock from within. In an arid climate, the story is different: there is simply not enough water to drive the reaction. Physical weathering — like the expansion and contraction of rock under intense heat — may dominate, but chemical solution is starved of its essential ingredient. So the same limestone that becomes a Swiss-cheese landscape of caves in Meghalaya may remain a stark, unyielding plateau in Rajasthan.

The dominant and almost exclusive geomorphic process in limestone areas is solution, also called carbonation. Rainwater, charged with carbon dioxide, forms carbonic acid:

Because the rock dissolves rather than erodes mechanically, the landforms it produces are entirely different from those carved by rivers or glaciers. The results are dramatic and distinctive:

• Sinkholes — circular depressions where the roof of an underground cavity has collapsed, or where surface water has dissolved the rock directly.
• Caves and caverns — vast underground chambers formed as acidic water enlarges joints and bedding planes over millennia.
• Underground drainage — streams vanish into sinkholes, flow through caves, and reappear as springs, leaving the surface dry and often barren.
• Stalactites and stalagmites — when calcium bicarbonate-laden water drips from cave ceilings, it deposits calcite as it evaporates, building icicle-like formations from above and pillars from below. …