A MODEL FOR PREDICTING THE OCCURRENCE OF COLLAPSE FEATURES ON CARBONATE ISLANDS AND COASTLINES

In the mid 1970s, Jim Quinlan had originally described the caves of Isla de Mona, Puerto Rico as “phantasmagorical” sea caves and attributed their origin to littoral erosion. Though he was not quite satisfied with that characterization, it was the only model that came close to explaining the existence of the very large caves of Mona. In the early 1990’s, a cave genesis model originally developed from the Bahamas was applied to cave development on Isla de Mona. This model explains caves, not only on Isla de Mona but on carbonate islands in general, as being the result of mixing zone dissolution in the distal margin of the fresh-water lens, under the flank of the enclosing land mass. Field work in the geologically complex Mariana Islands in the late 1990s resulted in the development of the Carbonate Island Karst Model, or CIKM, which integrated the various components controlling cave and karst development on carbonate islands. Characterization of caves types on carbonate islands was attempted using morphometric analysis of cave size and shape parameters, with limited success. Current research on seemingly random collapse features on carbonate islands, called “banana holes” in the Bahamas, has identified them as facies restricted and may provide a predictive measure of these features. Coastal reentrants, long thought to be stable because they are protected from wave energy, are now recognized as important sites for flank margin cave development. These features are not always evident if their entrances have not yet been erosionally breached. Flank margin caves and other associated features that occur on carbonate islands pose unique environmental problems with respect to residential and commercial development. These features tend to have a shallow horizon of development along with thin overburden making them prone to collapse. The current model for the development of coastal karst features provides a mode for predicting the location of potential collapses.