You are a US citizen and: 1  You are a first time applicant age 18 or older. 2  OR your most recent U.S. Passport was issued when you were under age 16. 3  OR your previous U.S. passport was issued more than 15 years ago.
Cave formations are called speleothem, from the Greek word spelaion, cave and thema meaning deposit. Almost all of them are made of calcite, the crystal of calcium carbonate. Different minerals and different movements in the water account for an incredible variety of cave formations.
Nearly all caves open to the public are of this type. These caves are called SOLUTION CAVES formed in rocks such as limestone or dolostone. They are part of a unique kind of landscape containing sinkholes, sinking streams, and springs. This landform type is called KARST, named for a plateau in western Slovenia. About 10-15% of the worldâs surface is karst.