UIS Commission on Karst Hydrogeology and Speleogenesis
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Glossary of Karst and Cave Terms

blue hole
1. Deep resurgence pool, notably in Jamaica and Florida, that may have a blue color due to the presence of algae. Also a deep submarine cave of the Bahamas. The latter type are large flooded shafts cut into the limestones of the shallow reefs and lagoon floors. Many are 100 m in diameter and some are 100 m deep. Opening from the shafts are flooded cave passages at various depths, some of which have been explored subhorizontally for more than 1 km. Their origins are complex. Extensive stalagmite deposits show that large old caves were drained when sea-levels were low during the Pleistocene (when water was held in the ice sheets). They are now being modified by marine dissolution, notably at the interface between fresh and salt waters (sea littoral zone) and by powerful tidal flows between connected holes [9]. 2. (Jamaican.) A major emergence where water (artesian spring) rises from below without great turbulence. 3. (Bahamas.) A drowned solution sinkhole [10]. 4. Caribbean expression for a major quiet up-welling karst spring inland or along the coast. The blue color is due to the scattering of sunlight by water molecules, although in some cases it may be attributed to the presence of calcareous algae [20]. Synonyms: (French.) source bleue (Jura), bleu-fon (South of France); (German.) Blaue Grotto; (Greek.) galapo speleo. See also boiling spring.