Groundwater naturally contains carbon dioxide (CO2) that allows it to dissolve limestone and form caverns. Here's how it works:

1. CO2 in the Soil: Rainwater absorbs CO2 from the atmosphere and the soil as it percolates through the ground.

2. Formation of Carbonic Acid: When CO2 dissolves in water, it forms carbonic acid (H2CO3). This is a weak acid, but it's still strong enough to react with limestone.

3. Dissolving Limestone: Limestone is primarily made of calcium carbonate (CaCO3). Carbonic acid reacts with calcium carbonate, creating calcium bicarbonate (Ca(HCO3)2), which is soluble in water.

This process is called karst weathering. The dissolved calcium bicarbonate is carried away in the groundwater, leaving behind empty spaces that can eventually become caves and caverns.

Here's a simplified chemical equation:

CO2 (g) + H2O (l) ⇌ H2CO3 (aq)

H2CO3 (aq) + CaCO3 (s) ⇌ Ca(HCO3)2 (aq)

Where:

* (g) = gas

* (l) = liquid

* (aq) = aqueous (dissolved in water)

* (s) = solid