|Cave formation begins when
rainwater absorbs carbon dioxide as it falls through the atmosphere. Rain
water must have carbon dioxide to become acidic. It must be acidic to chemically
react to the limestone bedrock. Rainwater is absorbed by the soil into the
As rainwater comes through the soil it absorbs more carbon dioxide that is being produced by plants that are dead. This changes the ground water to a weaker form of carbonic acid(H2O + CO2 = H2CO3). As it travels down through the ground it comes to solid rock. When the rock is limestone or dolomite caves can form.
The water reacts chemically with limestone and slowly a larger and larger space will form. This happens because the rocks are made of calcium carbonate (CaCO3). This is what you call chemical erosion.
As the space becomes larger and larger the water can flow through. As it flows it erodes . Physical erosion washes away rock and sand. This is what makes a cave larger and forms an underground stream. Finally over hundreds of thousands of years or even millions of years the cave is formed.
Here is an activity that you can try. Mix a mild acid (vinegar) with a base (baking soda). The reaction of the two substances illustrates the process carbonic acid dissolving limestone, but actual limestone solution by carbonic acid is a weaker, less noticeable reaction.
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