Cave Springs Earth Cache EarthCache

Not all caves are created equal - in fact, no two are exactly alike. There are different kinds (ice, karst, volcanic tubes, sea caves) and they are formed by many different processes (chemical, erosion, wave action, subsidence, dissolution, lava flows). No one is able to accurately predict how long it takes a cave to form. There are just too many variables, and often these are unobservable since they are underground. Forces such as streams, wind, lava, acid rain or ocean waves over time can carve out spaces large enough for us to walk in. Cave Spring, as the name connotes, serves as the discharge point for an unseen, underground river. If you were to look around this area, you would find the closest creek is near the campground, but its elevation is lower than the elevation of the Cave Spring. So this creek cannot be the source of the spring – in fact, the spring actually feeds this creek. Therefore, the recharge zone of the spring must be underground, invisible to us.

Not all bedrock is solid. Karst is a German word derived from the Slovenian "Kras" which means bare, stony ground. It was originally used to describe a limestone plateau near Trieste, Slovenia. Now the term means any landscape with distinctive landforms and hydrology shaped by the dissolution of a layer or layers of soluble bedrock, usually carbonate rock such as limestone (calcium carbonate, CaCO3) or dolomite (calcium magnesium carbonate, CaMg(CO3)2). Both of these rock types are slightly soluble in water. Karst terrain is characterized by springs, caves, sinkholes, and aquifers that are highly productive but also vulnerable to contamination.

About 20 percent of the land surface in the U.S. is classified as karst. Other parts of the world with large areas of karst include China, Europe, the Caribbean, and Australia. In the United States, about 40% of the ground water used for drinking comes from karst aquifers. In western Virginia, karst terrain occurs along slopes and in valleys between mountain ridges.

For most areas in western Virginia, a fairly limited range of rock types is present. One of the most important influences on a sedimentary rock's resistance to erosion is its quartz content. The more quartz a rock contains, the more resistant it will be to erosion. In western Virginia, sandstones generally consist mostly of quartz. Siltstones and shales (i.e. "fine grained [f.g.] clastics" ) are usually admixtures of quartz and other less resistant minerals. Limestones (i.e. "carbonates"), of course, are composed of calcite, which is rather susceptible to chemical weathering. However, some carbonate rocks do contain a fair amount of quartz -- especially in the form of chert -- and can be a bit more resistant to erosion than their more pure relatives. In addition, the carbonate rock dolomite is generally somewhat more resistant to erosion than limestone. Another equally important characteristic is how well the grains of a rock are consolidated -- known as its induration. Well indurated rocks have either intergrown crystals, or the grains are joined together with a lot of intergranular cement. Most limestones are initially well indurated. The induration of sandstones, siltstones, and shales (i.e. "clastics") varies from outcrop to outcrop. In addition, over time, weathering may dissolve the cement and weaken the rock. Quartz cements are very resistant to dissolution. Calcite cements dissolve rather readily. Iron oxides and clay minerals are fairly susceptible to chemical alteration. As a result of these two factors -- composition and induration -- sedimentary rocks display a wide range of susceptibility to erosion. Generally, well-indurated quartz sandstones are the most resistant to erosion. Likewise, limestones and poorly indurated shales are the most susceptible to erosion. Other sedimentary rock types are a bit more difficult to place within this spectrum. For example, all else being equal, a moderately indurated siltstone would probably be a bit less resistant to erosion than a moderately indurated conglomerate -- unless the siltstone has quartz cement and the conglomerate has calcite cement. Then the rates of resistance would be reversed.

Rain can collect carbon dioxide as it falls to the earth forming a weak carbonic acid (acid rain). The addition of carbon dioxide greatly increases the solubility of the water. Once rain has been absorbed by the soil it picks up additional carbon dioxide from decaying organic matter and plants. In this way the water passing through the soil and into the underlying rocks has the capacity to dissolve limestone and dolomite. The ground water enters cracks and fractures in these layered rocks and begins to dissolve it. When the water reaches an underlying layer of impenetrable rock, the water moves sideways, forming an underground river.

Subterranean water follows difficult to predict paths, bearing little relationship to surface topography. Depending on the acidity of the water and the path it takes through the rock, a cave may form. If it finds an exit from the rock, this is called a spring. Most karst groundwater returns to the surface at springs near streams and rivers like this. Depending on the constancy of the water source: there are three types of water flows; ephemeral, intermittent and perennial. An ephemeral waterbody is a wetland, spring, stream, river, pond or lake that only exists for a short period following precipitation or snowmelt. They are not the same as intermittent or seasonal waterbodies, which exist for longer periods, but not all year round.

To claim credit for the find, please email me the answers to these questions:

1. What are the approximate dimensions of the cave entrance?

2. Is the spring ephemeral, or perennial?

3. What kind of stone do you think forms the structure of the cave?

You are welcome to post photos of your visit to the site, but this is optional and not part of the logging requirements.