The white, sandy seafloor near the shallow waters of the Bahama Islands occasionally
drops away to disappear in a dark blue pool below the transparent waters. Reaching
hundreds of feet deep, these pools are called blue holes and are actually subterranean
caverns. They were formed around 18,000 years ago when a giant continental icecap
removed oceanic waters and lowered the sea level by hundreds of feet. During that era,
the Bahama Islands were hills on a large plain. Rainwater was made acidic by tropical
vegetation, and seeped into the soil to erode and dissolve limestone bedrock, creating
the underground caverns. Some caverns collapsed under the weight of the topsoil, and
became they type of sinkholes that occur in the Caribbean area. When the ice melted,
the seas rose and flooded the lowlands with water. The sinkholes, now covered by water,
became the famous blue holes.
Local folk stories claim the holes are the legendary lair of the lusca, an octopus-like
monster that comes out when hungry, churning the waters with its arms and dragging boats
under. Although no monsters live beneath the surface, blue holes can capsize boats. The
caves trap tidal flow inside their underwater passageways, creating quick currents that
create surface turbulence and whirlpools that can suck small vessels to the bottom.
Divers are also endangered by strong currents so the holes can only be explored safely
twice a day - when the tide and caverns are calm.
Inside the blue holes, divers find an amazing universe of rock and wildlife. Stalactites
are suspended from rocky roofs; blind, colorless fish dart through the depths; lobsters
and crustaceans crawl along the sandy floor; and other species found nowhere else in the
world live together.