Earth Cache

Let the Earth be your teacher!

The scientific study of caves is called 'Speleology'. One would expect it to be Caveology but in 1895 Édouard-Alfred Martel wanted "to make speleology something else than a mere sport." The root of Speleology is taken from the much older 'Spelaean' which means a person who dwells in caves. Today, the term can be used both ways but preference is given to Speleology for study and learning, while recreational exploration of caves is more properly referred to as caving or caverning.

Karst, on the other hand, is named after a German mineralogist named Dietrich Ludwig Gustav Karsten who lived over two-hundred years ago. The first mineral named after Karsten was Karstenite in 1813 and which means Anhydrous sulphate of lime or just simply Anhydrite. In the past few years, the word Karst has become very popular and is used as an umbrella term that refers to geological conditions, particularly those involving limestone, which favor the formation of caves as well as places of erosion.

How caves are formed

Upon entering a cave we notice two remarkable things. First is the fact we are in an underground cavern or tunnel (the cave), and the second is that it is usually decorated by a variety of rock formations (speleothems). Both the caves and the speleothems are formed by similar but slightly different processes.

Cave formation.

The caves at Wombeyan have been developed in marble which is a metamorphic rock composed of calcite. As water soaks through the ground it combines with carbon dioxide to form a weak acid which dissolves calcite. This acidic water flows through cracks in the rock and widens them. This is a process of erosion. The water moves quickly enough that it carries the dissolved calcite away and leaves nothing in its place. Eventually the cracks develop into caves.

Speleothem formation.

After a cave has formed, water passes downward through the soil above the calcite, absorbs carbon dioxide, and becomes acidic. As a weak acid, the water is able to dissolve a small amount of the calcite as it passes through cracks and pores on its journey down into the cave. As this water drips into the air-filled cave, dissolved carbon dioxide is given off. Because the water has lost carbon dioxide, it cannot hold as much dissolved calcite. The excess calcite is then precipitated on the cave walls and ceilings. This is a process of sedimentation. The water moves slowly and leaves deposits behind where they make up many of the different kinds of formations.

When the water moves slowly, sediment clings to the chamber ceiling to form stalactites, and when the water moves a little faster it falls to the floor where it forms stalagmites. If allowed to continue, a stalactite and stalagmite may grow into each other to form a column.

When the flow of water is obstructed or influenced by a variety of factors in the cave environment, it will create speleothems less uniform in appearance than stalactites and stalagmites. Many common speleothems are helictites, flowstones, rimstones, straws, and shawls.

Other speleothems give rise to creative interpretations and you will see many examples of these in the Fig Tree Cave.