FLFlorida Geography

Water leaving the southern rim of Lake Okeechobee does not enter a channel. It spreads out across a sheet of sawgrass up to sixty miles wide and creeps toward Florida Bay at roughly a hundred feet a day, losing about two inches of elevation for every mile it travels. Marjory Stoneman Douglas gave the thing its name in 1947 when she called it a river of grass, and the description is literal rather than poetic.

Okeechobee, the sawgrass, and the plumbing

Lake Okeechobee covers about 730 square miles with an average depth of only nine feet, making it the second largest freshwater lake lying wholly within the lower 48 states, behind Lake Michigan. The Kissimmee River feeds it from the north. Before drainage, the lake simply overflowed south in the wet season, and that overflow was the Everglades.

The 1928 Okeechobee hurricane pushed the shallow water over a low muck dike and drowned roughly 2,500 people, most of them farm workers in Belle Glade and Pahokee. The federal response was the Herbert Hoover Dike, 143 miles of embankment enclosing the lake. Between 1962 and 1971 the Kissimmee was straightened into a 56 mile ditch designated C-38, which drained the floodplain and wrecked the water quality downstream. Re-meandering work has been running since 1999 to put the bends back.

Big Cypress Swamp lies west of the sawgrass, on slightly higher limestone with strands of cypress instead of open marsh. Everglades National Park protects only the southern portion of what the system once was.

Limestone under everything

Florida is the exposed crest of the Florida Platform, a carbonate plateau roughly twice as wide as the visible peninsula. The rest of it lies drowned beneath the Gulf shelf on one side and the Atlantic shelf on the other. There is no ancient hard basement rock anywhere near the surface, only limestone and the sand sitting on top of it.

Rainwater picks up carbon dioxide in the soil, turns mildly acidic, and dissolves that limestone. The consequences define the state:

• Sinkholes. Cavities enlarge underground until the roof fails, sometimes under a road or a house.
• Springs. More than a thousand are named, and 33 of them are first magnitude, discharging over 100 cubic feet per second. That is a greater concentration than any other state or country.
• Disappearing rivers. The Santa Fe River drops into a sink at O'Leno State Park, travels about three miles underground, and rises again downstream.
• The Floridan aquifer. It supplies most of the state's drinking water and connects directly to the springs and sinks, which is why surface pollution shows up in them quickly.

Britton Hill, and the smallest relief in the country

The highest point in Florida is Britton Hill, 345 feet, in Lakewood Park in Walton County a few hundred yards from the Alabama line. It is the lowest high point of any state, and the ground just across that border in Alabama is higher. From summit to sea, Florida's total relief is 345 feet spread over 65,758 square miles.

The one real ridge is the Lake Wales Ridge, a chain of relict sand dunes running down the centre of the peninsula and reaching about 300 feet. It stood above water as an island when Pleistocene sea levels were higher, and its isolated scrub habitat holds plants and animals found nowhere else on earth.

Two time zones and 1,350 miles of coast

Florida is split by the clock. The panhandle west of the Apalachicola River keeps Central Time, while the peninsula and the eastern panhandle run on Eastern Time. The line follows the river and the Gulf County boundary, so Panama City and Tallahassee sit an hour apart despite both being in the panhandle.

The state has about 1,350 miles of general coastline, more than any state except Alaska, and 8,436 miles once bays, inlets, islands and river mouths are traced. It is the only state fronting both the Gulf of Mexico and the Atlantic Ocean, and no point anywhere in it is more than about sixty miles from salt water.

The Florida Keys curve southwest for 120 miles as exposed Pleistocene reef, Key Largo Limestone in the upper keys and Miami Limestone in the lower. Key West sits at 24 degrees 33 minutes north, closer to Havana than to Miami, and Ballast Key just beyond it is the southernmost land in the continental United States. The only living coral barrier reef in the continental country lies a few miles offshore.

Storms, heat and a record low of minus two

Florida has absorbed more hurricane landfalls than any other state, roughly 120 since systematic records began in 1851, close to forty percent of the national total. The Labor Day hurricane of 1935 crossed the middle keys with a central pressure of 892 millibars, still the lowest ever measured at a landfall in the United States.

Extremes on land are milder than the storms suggest. The record high is 109 degrees Fahrenheit at Monticello on June 29, 1931, lower than the record in states far to the north, because sea breezes and afternoon thunderstorms cap the heat. The record low of minus 2 degrees at Tallahassee on February 13, 1899 is the warmest state record low anywhere in the mainland United States. Annual rainfall runs 50 to 60 inches, most of it delivered in summer convection, and the corridor between Tampa and Orlando records more lightning strikes per square mile than anywhere else in the country.

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