Rainwater causes limestone to dissolve through a chemical weathering process.
The Chemical Reaction
When it rains, rainwater mixes with carbon dioxide in the atmosphere, including that produced by animals. This combination creates a weak carbonic acid.
- Carbon dioxide (CO2) + water (H2O) = carbonic acid (H2CO3)
This weak carbonic acid then reacts with limestone, which is primarily made up of calcium carbonate (CaCO3).
- Carbonic acid (H2CO3) + calcium carbonate (CaCO3) = calcium bicarbonate (Ca(HCO3)2)
The reaction converts the relatively insoluble calcium carbonate into a soluble calcium bicarbonate, which rainwater can easily wash away.
Impact on Limestone Landscapes
The process of rainwater dissolving limestone leads to significant changes in limestone landscapes over time:
- Erosion: Gradual removal of limestone, creating features like caves, sinkholes, and gorges.
- Cave Formation: The dissolution process is often most prominent underground, creating vast cave systems.
- Karst Topography: Over time, areas with significant limestone deposits develop a unique landscape known as karst, characterized by these distinctive features.
- Sinkholes: Form when underground cavities collapse.
- Caves: Form from the erosion of limestone.
- Springs and Streams: Appear from the water that has permeated the limestone.
Summary
| Aspect | Description |
|---|---|
| Reaction | Rainwater with carbonic acid dissolves limestone |
| Chemical Change | Calcium carbonate converted to soluble calcium bicarbonate |
| Result | Dissolution, erosion, formation of caves and karst landscapes |
