THE FORMATION OF CONDUIT CAVES IN THE BAHAMAS

Conduit caves are found in the Bahamas starting at depths of 15m below modern sea-level. Originally these conduit caves were hypothesized to form when sea-level was lower and island size increased by an order of magnitude such that catchment area increased by the square, but the discharge perimeter only increased linearly. Under these conditions, it was proposed, aquifers could no longer drain effectively under diffuse flow. However, recent modeling demonstrates that the large islands are capable of still draining under diffuse flow conditions given the initial eogenetic characteristics of the limestone in the Bahamas. Because the Bahamian aquifers are made of carbonates they are continually self-modifying and over time touching-vug permeability develops. When touching-vug permeability develops islands smaller than 5 to 10km in radius effectively drain under diffuse flow, and conduit flow cannot be supported by the water budget. Islands larger than 10km radius generate sufficient water competition within the touching-vug system which leads to conduit development. In other words, conduit development in the Bahamas is not a matter of discharge restriction, but rather of recharge abundance. Recharge rates based on climate also control the development of conduit flow; however, island size is more significant. The conduit caves in the Bahamas are significant in that they may collapse and if this collapse reaches the surface a progradational collapse blue hole is created.