BLUE HOLES, CONDUIT CAVES, AND WHITINGS OF THE BAHAMAS

Blue holes are found across the Bahamian archipelago and are formed by: 1) vadose dissolution during a previous sea-level lowstand; 2) bank margin failure; and 3) progradational collapse into a void at depth. Progradational collapse blue holes are found across all of the larger platforms (Great Bahama, Little Bahama and Cay Sal) in both inland and ocean environments, but not on the smaller platforms. Progradational collapse blue hole distributions can be estimated based on known blue holes and this can be extrapolated across the platforms to estimate the total number of progradational collapse blue holes on each platform. Additionally, only on the larger platforms are there conduit caves. These conduit caves are known because they intersect the progradational collapse blue holes and are the incipient voids into which the collapse occurs.

Conduit caves in the Bahamas are only found greater than ~10m below modern sea-level. When sea-level drops by this much the Bahamian platforms are exposed and the surface area of the islands increases significantly. Sea-level has varied significantly over the Quaternary and the conduit caves match the sea-level lowstands and highstands that are less than 10m below modern sea-level.

Conduit cave formation appears to be dependent on both recharge rates to the aquifer and island size. The greater the island size and the greater the recharge rate the more likely that conduit caves will form. It so happens in the Bahamas that the larger platforms are in the regions with higher recharge rates which is where the conduit caves form and that the smaller platforms are in the regions with lower recharge rates and there are no conduit caves on those platforms.

Finally, progradational collapse blue holes and the conduit caves have significance for whiting formation in the Bahamas. Whitings are formed by tidal pumping of water through the sediment filled blue holes that are connected to the conduit caves. When the water reaches the surface aragonite is precipitated through the warming of the water and the degassing of CO₂, resulting in the formation of whitings. This model explains the chemical, biological, and physical observations related to whiting formation that has been an enigma for half a century.