The Bahama Banks are the submerged carbonate platforms that make up much of the Bahama Archipelago. Here, most the of the islands comprising this archipelago and their respective platforms are visible.
The largest of the platforms are the Great Bahama Bank around Andros Island, the Little Bahama Bank of Grand Bahama Island and Great Abaco, and the Cay Sal Bank north of Cuba.
The limestone that comprises the Banks has been accumulating since at least the Cretaceous period, and perhaps as early as the Jurassic; today the total thickness under the Great Bahama Bank is over 4500 meters.
The waters of the Bahama Banks today are very shallow; on the Great Bahama Bank they are generally no deeper than 25 meters. This is evidenced by the light blue water color.
The slopes around them, on the other hand, such as the border of the Tongue of the Ocean (the large curve at the bottom right) in the Great Bahama Bank, are very steep. The exact place where the platforms end and the slopes plunge downward can be observed as the sudden change from light turquoise to navy blue water.
Despite the fact that they are submerged today, the Banks were dry land during past ice ages, when sea level was as much as 120 meters lower than at present.