Microbial Diversity of Cave Ecosystems
The formation of natural caves (speleogenesis) is due to any number of processes that result in the hollowing out of rock, including dissolution, mechanical weathering, volcanic activity, or even the melting of glacial ice. Caves are classified based on the solid rock that they developed within, the proximity to the groundwater table (e.g., above, at, or below it), the speleogenetic history of a feature, and the overall passage morphology and organization (e.g., cave length, passage shape, passage arrangement, passage levels) (Fig. 10.1). Caves are one type of feature that characterizes a karst landscape, which develops in soluble rocks (e.g., limestone, dolomite, gypsum, halite) that roughly coincides with the global distribution of carbonate sedimentary rocks of all geologic ages (e.g., Ford and Williams 2007). Although karst comprises ∼15–20% of the Earth’s ice-free land surface, karst caves are not interconnected, not within the same hydrological drainage basin and definitely not across different drainage basins.