Karst Topography

Are you adventurous enough to go below the surface of the Earth and study in a deep and dark cave? Beneath the surface of the Earth, there are countless miles of caves that have yet to be explored. Some caves are extremely deep, others are very large, and others require scientists to have to squeeze through tight openings. Some caves are even known to produce giant crystals. Even as scientists explore these marvelous systems, caves remain some of the least explored areas on the planet.

Karst topography is a landscape consisting of caves, caverns, and sinkholes, and it typically found in areas with limestone or dolomite bedrock. To best understand how this type of geological formation is created, it is important to know the properties of limestone rock. Most of the cave systems of the world are formed in the sedimentary rock limestone, which covers an estimated 10% to 25% of Earth’s surface. Limestone is an organic sedimentary rock that forms in shallow marine environments. Essentially, limestone is the exo-skeletal remains of ocean organisms like those that can be found in present day coral reefs. Over thousands of years, oceans can evaporate or disappear through tectonic activity, causing these ocean deposits to exist in dry, continental areas. All limestone is chemically identical to the mineral calcite (CaCO3), which belongs to the carbonate mineral group. As a carbonate, limestone is highly reactive with acids.

Couresry of Virginia Department of Geology and Mineral Resources

Areas in Virginia that contain karst topography.

The caves of Virginia are found in areas with limestone bedrock. This means that those same areas were once underneath ocean water. Evidence of this can be found in the rock as geologists are able to extract ocean fossils. The majority of cave systems in Virginia are found in the areas west of the Blue Ridge Mountains, which are highlighted in red on the map image.

There are many different acids that exist in nature, and the most prevalent is rain water. All rainwater is slightly acidic due to the absorption of carbon dioxide gas from the air. This natural acid, called carbonic acid, falls from the sky every time it rains and then runs off on the surface or infiltrates into the ground. When rain infiltrates the ground, it passes through pore spaces in the rock and eventually becomes groundwater. When rain infiltrates limestone, it reacts with the carbonate rock and dissolves it. This process happens slowly, and eventually, holes begin to develop in the rock beneath the surface of the Earth. As time passes, more rain will result in more infiltration, and the water continues to carry away the limestone rock in solution. The end result is a series of holes underground called caverns. If the hole is exposed to the surface of the Earth, then it is called a cave or cavern. This method is the most common method of cave formation. Another way that caves can form takes place when groundwater comes into close contact with sulfide minerals, or by bacteria within the groundwater which break down rock as a normal process of their life cycles. This creates a very strong acid called sulfuric acid. This acid is stronger than carbonic acid and can really create some spectacular features. In many caves, the path of water has become large and will create underground rivers.

Cave Features

There is a system of caves and caverns in the western region of Virginia called Luray Caverns. The Luray Caverns, like most cavern systems, are filled with unique and impressive features that are unique to caverns. In this activity, explore the many features that form in a cave. Click the player button to begin.

View a printable version of the interactivity.

 

Karst Topography Review

Now that you have investigated karst topography, practice what you have learned. In this non-graded activity, read each statement and decide if it is True or False. Click the player button to get started.