Key Biscayne is known as a barrier island, and is found at the bottom end of a chain of islands that stretches along the southeastern coast of Florida. Barrier islands are build-ups of sand that form along the coast of larger land-bodies. Key Biscayne was formed over thousands and thousands of years as currents that run parallel to the shore of Florida deposited sand on a hard layer of underwater rock. This rock, called Key Largo Limestone, is made from the fragments of ancient coral reefs. The deposited sand was then shaped by the wind and the waves into its current form, the island that we see today.
However, this process of deposition and erosion is ongoing. The wind and the waves of the Atlantic continue to shape the island today, and over the years humans have tried various ways to counteract this natural process. In the 1940s, various jetties, bulkheads and groins were installed to keep the island from shifting and changing shape, and in 1987, sand from offshore was used to replace sand along the beaches that had been washed away over time. Still, the wind and the waves continue to slowly but surely shape the island, a powerful testament to the power of nature.