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BLUE HOLES - THE BAHAMAS

Found on both land and in the ocean throughout the Bahamas are deep circular cavities known as Blue Holes which are often the entrances to cave networks, some of them up to 14 kilometres in length. Over time the limestone of the islands was eroded by water and vast cave networks created.  When sea levels rose again about 10,000 years ago some of these collapsed inwards land the Blue Holes were formed