2. Formation Caves are formed by geologic processes. These may involve a combination of chemical processes, erosion from water, tectonic forces, micro-organisms, pressure, and atmospheric influences. Most caves are formed in limestone by dissolution.
3. Formation cont. <ul><li>Some caves are formed at the same time as the surrounding rock. These are sometimes called primary caves . </li></ul><ul><li>Sea caves are found along coasts around the world. A special case is littoral caves , which are formed by wave action in zones of weakness in sea cliffs. Often these weaknesses are faults, but they may also be dykes or bedding-plane contacts. Some wave-cut caves are now above sea level because of later uplift. </li></ul>
4. Formation cont. <ul><li>Ice caves </li></ul><ul><li>Glacier caves occur in ice and under glaciers, formed by melting. They are also influenced by the very slow flow of the ice, </li></ul><ul><li>Fracture caves are formed when layers of more soluble minerals (soluble rock) </li></ul>
5. Formation order Phreatic cave passages (or phreatic tubes ) are formed below the water table by water flowing under pressure. They can vary in size from a few centimetres to several metres in diameter.
6. Formation order A stream flowing along the bottom of a phreatic tube The stream gradually begins to carve a trough in the bottom of the tube. This is called the vadose stage of development
7. Formation order A Keyhole Passage Eventually a "key-hole" shaped passage may be formed with the stream flowing at the bottom of a deep rift. Progress along these passages may be made by walking along the bottom of the rift. However, the rift may be so narrow that cavers will need to traverse along the tube at the top.
8. Formation order A Breakdown Chamber Eventually the water may form enormous caverns and a period of breakdown, where large boulders crash down from the cave roof, begins. Ancient waterways may become completely abandoned and are called fossil passages