Limestone is primarily eroded through a chemical weathering process called carbonation.
Here's a breakdown of how it works:
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Rainwater and Carbon Dioxide: As rainwater falls, it absorbs carbon dioxide (CO2) from the atmosphere and the soil.
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Formation of Carbonic Acid: This absorption creates a weak carbonic acid (H2CO3) solution. The chemical reaction is:
H₂O (water) + CO₂ (carbon dioxide) ⇌ H₂CO₃ (carbonic acid)
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Carbonic Acid Dissolves Limestone: The slightly acidic rainwater then seeps into cracks and fissures in the limestone rock (calcium carbonate - CaCO3). The carbonic acid reacts with the calcium carbonate, dissolving it. The chemical reaction is:
CaCO₃ (calcium carbonate) + H₂CO₃ (carbonic acid) ⇌ Ca²⁺ (calcium ions) + 2HCO₃⁻ (bicarbonate ions)
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Removal of Dissolved Rock: The calcium ions and bicarbonate ions are carried away in the water, effectively eroding the limestone.
In summary, the weak carbonic acid dissolves the calcium carbonate in the limestone, gradually eroding the rock over time. This process is responsible for the formation of many karst landscapes, including caves, sinkholes, and disappearing streams.
