Abstract:

Four caves and two underground streams in granite occur within the Girraween National Park. Only two of these sites have previously been reported. They mainly occur on the margins of major joints in the granite where streams descend into troughs along the joints. The caves are themselves formed in minor joints. In some cases streams have worked their way down from the surface along a joint but at three of the sites streams flow through horizontal joints in the granite which have not been opened from the surface. For these sites it is not clear how the initial passage was opened up underground. The two possible mechanisms suggested here are solution and joint opening following pressure release. The cave morphology clearly indicates that once the path flow is open, abrasion becomes the major process. Flowstone terraces, 'cave coral', and cemented gravels are found in the caves. The speleothems and the cement are amorphous silica (Opal A). Caves in granite may be more common than was previously thought.