Rainwater can dissolve limestone, creating caves and features that appear to have dripped into place.
Limestone is a type of sedimentary rock that is often formed in warm, shallow saltwater seas. The rock is made from the sediment, including corals and shells, that drifts to the bottom of the water and is compacted over time. The primary mineral in limestone is calcium carbonate. Limestone has numerous effects on the landscapes where the rock is found.
Caves
Limestone can be dissolved by acidic solutions. Since rainwater is naturally slightly acidic due to chemicals such as carbon dioxide in the atmosphere, rain sculpts limestone landscapes over time. On the surface, the rainwater can create pitted features and rock flutes. Underground, rain and streams can carve out massive caves and create aquifers.
Sinkholes
The caves that are formed in areas with a lot of limestone, known as "karst terrain" by geologists, can collapse. When they do, a sinkhole is formed. Sometimes these sinkholes can be quite shallow, but at other times, a new sinkhole can swallow a house or part of a highway. In the United States, sinkholes are common in Texas, Alabama, Tennessee, Missouri, Kentucky, Florida and Pennsylvania, according to the U.S. Geological Survey.
Water Quality
Limestone areas can cause "hard water," which is formed when the calcium carbonate in the limestone dissolves into the water that passes over it. Hard water isn't harmful to your health, but it can makes it difficult of create suds or a lather with soap. Hard water can also be a problem for industrial water users.
Aquifers
While hard water isn't harmful, limestone landscapes can make it more likely that drinking water from a well will be contaminated. Because water can travel very quickly underground in karst terrain instead of trickling through the earth in other landscapes, contaminants such as pesticides and fertilizer can be carried directly to a well without being filtered by the surrounding soil.
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