The Banks

Great Sale Cay, Bahamas
N 26 59.16 W 078 13.06

These Bahamas Banks are amazing. I never paid much attention to them before in my studies of geography.

Imagine a plateau, sort of like the bluffs one sees in the Western US. However, these plateaus are more than a hundred miles wide and they are almost as flat as a table on top. The plateau rises 4 kilometers above the surrounding territory. Now, for reasons I don't understand, suppose the top of this table is just 3 meters below sea level. That's what we have in the Bahamas. Come to think of it, that is also what we have in Florida except that Florida is 3 meters above sea level.

Now consider the tides. There is about 1 meter of tide here. That means that 1/3 of the water on top of the banks is flushed out and replaces twice per day. No wonder the water is so clean and clear. It also means that the tidal currents here on the banks are swift and strong.

Next consider the waves. No matter how hard the wind blows, waves on the banks will never get more than 3-4 feet high. Bigger waves would be cut off by the shallow bottom. At the fringes of the bank however is a different story. On the eastern side, the edge is defined by a chain of islands. The seas and swells of the North Atlantic are forced up from 4000 meters depth to 4 meters depth as they are squeezed between those islands. In addition, all that tidal water must ebb and flow twice per
day, regardless of waves. It all adds up to huge and dangerous waves in those gaps between the islands. The Bahamians call that The Rage.

The flat table top is spoiled in a few places where the land is a bit higher. Those places are the islands, or cays as most of them are called here. The cays are mostly infertile and have no minerals, oil or fresh water of their own. Small wonder then, they were never heavily settled.

I wish my knowledge of geography was better. I've wondered before how such huge stretches of land can just accidentally lie just a few meters above (or below) sea level. Even more amazing are the salt marshes. They cover thousands of square miles with land at a level just a few centimeters below sea level. Those levels don't sound accidental to me. There must be some feedback mechanisms in place to keep them stable. On visible mechanism is the mangroves forests, but there are no mangrove
forests here.

We sailed only 20 miles today to Great Sale Cay. I went snorkeling and Libby and I explored the shallow waters a bit with the dinghy. Tomorrow we'll go ashore and explore the shallows some more.

Now, about an hour before sunset, the biggest, grandest, most beautiful thundercloud I ever saw is approaching from the west. What a shame that I can't post pictures with SSB email. That cloud must be more than 100 miles long. It is shaped like a cone, and at it's tip is the storm. I hear thunder from far away but can see no flashes.