Caves in granitic rocks: types, terminology and origins

Abstract

Caves or openings of various shapes and sizes are well and widely developed in granitic rocks as well as in other lithological environments. Some are caused by preferential water-related weathering, e.g. hydration, others to sapping, but haloclasty plays a crucial role in the development of tafoni. These are especially well represented in granitic exposures. This can be explained partly because the inherent strength of the crystalline rock permits hollowed blocks, boulders and sheet structures to remain standing. The hollows themselves owe their origin partly to the susceptibility of feldspar and mica to hydration and other forms of water-related alteration, and also to the capacity of haloclasty to rupture and break down the rock. On the other hand, dry granite is relatively stable and, particularly if it is cemented by salts concentrated at and near the surface by lichens and mosses, it forms the crusts or enclosing visors that are an essential part of tafoni morphology.