1. How Rainwater Slowly Dissolves Limestone Rock
Limestone is a rock formed from the accumulated shells of ancient corals and sea creatures on the ocean floor. [1] Rainwater absorbs carbon dioxide from the air, becoming slightly acidic. When this water touches limestone, it slowly dissolves the rock. [1]
The amount dissolved in a single year is tiny. However, if this process continues for tens of thousands of years, the rock is significantly eroded. This long-term erosion creates mountains and valleys with strange shapes. [1]
2. Similar Limestone Scenery in China, Vietnam, and Other Countries
In Guilin, China, you can see a landscape of pointed, rugged mountains. [2] In Ha Long Bay, Vietnam, many small rocky islands float on the sea. [2] The term "karst" itself comes from the name of a region in Slovenia called "Kras," where this terrain was first studied academically. [2]
Japan also has karst terrain. Akiyoshidai in Yamaguchi Prefecture is the largest limestone plateau in Japan. [3] It began about 350 million years ago as a coral reef in a warm sea. Over a long time, it changed into limestone and was then dissolved by rainwater to form its current shape. [3]
3. Why the Ground Above Limestone Can Suddenly Collapse
Beneath limestone landscapes, there are many hidden holes and tunnels created by water dissolving the rock. Usually, the soil on top covers these voids, so people do not notice them. But if that cover breaks, the ground can suddenly collapse. [4]
In 1981, in Winter Park, Florida, USA, a large hole opened in a town area overnight. It was about 90 m (about 300 feet) wide and about 24 m (about 80 feet) deep as seen from the surface. [4] One house, part of a swimming pool, five sports cars, and one truck parked at a repair shop were swallowed by the hole. Fortunately, no one was injured. [4]
4. Underground Rivers and Caves Carved Under Limestone
Under limestone terrain, there are hidden underground rivers and caves that rainwater has carved over hundreds of years. [5] Beneath Akiyoshidai in Japan, there is a large cave called Akiyoshi-do. It is one of Japan's largest caves. [3] Passages continue for several kilometers. [3]
5. How Groundwater Stored in Limestone Supplies Drinking Water
Many regions use water stored underground in limestone as drinking water. It is said that about one-quarter of the drinking water used worldwide comes from this karst groundwater. [6]
In the United States, about 20% of the land is classified as karst terrain. About 40% of the groundwater used for drinking comes from these karst aquifers. [7]
6. Experiment: Dissolving an Eggshell in Vinegar
You can see a similar change by placing an eggshell in a cup of vinegar. After a while, bubbles appear, and the shell slowly dissolves. This is very similar to how limestone dissolves in rainwater. [1]
If you try this with chalk, note that chalk made of gypsum will not produce bubbles. [1]