- 1. Cave conceived and developed by dissolution, usually below the water table, where all voids are water filled within the phreas. Phreatic caves may include loops deep below the water table, particularly in dipping limestone with widely spaced bedding-related fissures. Higher fissure densities, subhorizontal geological guidance, or greater karstic maturity encourage shallow phreatic development just below the water table. Progressive abondonment of phreatic caves is usually in a downward sequence, as erosionally lowered valley floors intersect lower levels of the flooded system. Active phreatic cave segments, left perched for geological reasons after a general water-table lowering, are relatively common. Characteristics of phreatic caves are blind dissolution pockets on walls and ceilings, branching and looping of passages, and overall switchback gradients as phreatic flow may be uphill under pressure. The most common passage, and overall switchback gradients as phreatic flow may be uphill under pressure. The most common passage form is a tube, though crosssectional shape reflects local geological factors. A classic active phreatic cave is that behind the Fontaine de Vaucluse in France, while Hölloch, Switzerland, is a major system consisting mostly of relict phreatic passages .2. Cave passage developed in the phreatic zone and still actively forming. Passages often appear as tubes.
A Lexicon of Cave and Karst Terminology with Special Reference to Environmental Karst Hydrology. Courtesy of the author & The Karst Waters Institute. 2002.
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