Peggy Peterson, age 12, of Sarasota, Florida, for her question:
Why are there no mountains in Florida?
Florida has several hilly ridges where warm weather crops thrive on the fertile slopes. Bumpy uplands cross the north of the state and a raised ridge tilts down the center. Many hills rise 200 feet and the highest is 345 feet. Not one of them is high enough to be a real mountain.
The features of every stretch of land began to form billions of years ago. The face of the earth is constantly changing and events of the past have left their signatures in the rocky crust. One of the most dramatic geological stories is the age old conflict between the land and the sea. Time after time, the seas have invaded and then receded from vast areas of the land. One of the most recent of these battle fronts was won by the finger of land that makes up most of the state of Florida.
In terms of human history, Alaska was one of the last states to be added to our nation. But in terms of geological history, the last state to join the North American continent was the Florida peninsula, brought into being by the war between land and sea. This age
., old battle front includes a wider region reaching along the Atlantic and around the Gulf of Mexico. It also includes the molding of the ocean floor far out into the Caribbean and westward across the Isthmus of Panama.
About 500 million years ago, the sea swamped the Southern states, leaving a chain of eastern islands, one near Jacksonville. Then the sea lost ground and Florida's small island extended to borders of dry land around the Gulf. Between 200 and 300 million years ago, the Gulf coast gained more ground, but the Florida peninsula was still submerged. About 100 million years ago, vast areas of ground were lost again. The northern Gulf Coast and all of Florida were submerged until the Miocene Period of 25 million years ago.
Mountain making is a massive operation, upsetting a vast region for ages. About 200 million years ago, the Southern Appalachians arose and walled off the sea. This was Florida's last change to gain mountains, but the ridge did not extend far enough to lift the peninsula above the water. But under the water, the future features of Florida were being molded. The Panama Ridge arose, linking the two Americas for the first time. New tidal systems in the Atlantic shaped shoals and sandbanks on the seabed. Corals built reefs and breakwaters. Streams from the land dumped sediments 5,000 feet thick on the ocean floor.
These patient, underwater events molded the shape and the flat, rocky strata of Florida. Then came the Ice Ages, crushing half of North America. In the past million yeas, vast regions sank and uplifted as the glaciers came and went four times. The massive ice fields took their moisture from the oceans, much of it from the warm, moist Gulf of Mexico. The sea level sank and for the first time, the flat, lower lying Florida peninsula lifted above the waves.
The coast of the newly born peninsula is still just a few feet above sea level. Its rocky layers are coral and limestone deposited by small ocean creatures topped with sandy sediments of sand and rich silty soil. The uplands of the north and center are much older layers. In the past they may have been higher, but never as high as mountains.