File:Purslane Pit (San Salvador Island, Bahamas) 1 (16467167132).jpg

Purslane Pit (looking ~west), northeastern San Salvador Island, eastern Bahamas. (photo taken by Mark Peter)

Several categories of karst (dissolutional features in soluble rocks such as limestone) exist on islands in the Bahamas. Common small-scale karst features include phytokarst and solution tubes. Large-scale karst features include flank margin caves, pit caves, banana holes, lake drains, and blue holes.

San Salvador Island has numerous inland ponds and lakes that range in salinity from normal marine to hypersaline to hyposaline to brackish. Many of these lakes have obvious tidal fluctuations, indicating that there is connectivity with the ocean. The nature of the plumbing system between the ocean and the inland lakes is largely unknown. Lakes having tidal fluctuations usually have an obvious lake drain (tidal inlet) through which water enters and exits.

The feature shown above is Purslane Pit, an ephemeral inland pond that is normally covered in a greenish & reddish, low-growing succulent called the sea purslane, Sesuvium portulacastrum (Plantae, Angiospermophyta, Caryophyllales, Aizoaceae). A small opening in the limestone bedrock on the western side of the depression is a lake drain (= small grayish area where person at center is pointing). Most lake drains reported in the San Salvador geology literature are small. Some are big enough for a person to enter. Underwater exploration of larger lake drains has shown they do not extend far before narrowing to inaccessability. See Godfrey et al. (1994) for more info.

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