Where Did Florida’s Sand Come From?

Florida is of course famous for its sandy sunny beaches. Most people assume that this sand comes from broken and crushed coral, and for a small portion of the state that is true. But for most of Florida, the source of all that beach sand is far more interesting.

P1030328

Florida beach


About 300 million years ago, the tectonic plates that made up all of the world’s continents began to move closer and closer together. Over time, they stuck together into a vast new supercontinent known as “Pangaea”. But the momentum of these enormous slowly-moving rock masses generated intense pressure, and along the border of the African and North American plates, where they were crunching together, the rock layers began to compress and fold upwards–like the ridges you can make by pushing in at the edge of a rug. The imposing “thrust faults” formed by these immense geologic forces would later be known as the Appalachian Mountains. They were an enormous range, stretching all the way from Maine to Georgia, and soaring to perhaps a higher elevation than today’s Himalayas.

Today, at 6,000 feet, the Appalachian Mountains are only a shadow of their former selves. Once lofty craggy barren snow-covered peaks, they are now a mere fraction of their former height, weathered into a ridge of low rolling tree-covered hills. At least 15-20,000 feet of the mountain range is now gone. So, what happened to all that rock? Where did the rest of the Appalachians go? To answer that question, we have to take a closer look at Florida.

About 225 million years ago, tectonic forces began to break Pangaea apart and create the Atlantic Ocean, with North and South America moving to the west and Europe and Africa to the east. But as they moved further apart, a small part of the African plate remained behind, stuck to the North American plate. This chunk of bedrock, consisting of black glassy volcanic basalt, became Florida.

During the time of the dinosaurs, Florida was at the bottom of a warm shallow tropical sea. Over a period of millions of years, ocean sediments, mostly from the shells of tiny marine creatures, built up at the bottom of this sea and, as the layer got thicker and heavier, became compressed over time into limestone.

At the same time, the Appalachian Mountains were steadily eroding away, grain by grain, as wind and rain inexorably wore down the mighty peaks. These eroded silica grains, weathered out of the rock, were carried as sand in meltwater streams down the side of the mountains and into creeks that flowed down the valleys. These in turn joined into rivers, some larger than today’s Mississippi, and, eventually, ran all the way to the seacoast in what is now southern Georgia. Here, the powerful current carried the sand grains far offshore, until they lost enough energy to settle on the shallow sea floor, forming thick layers over the limestone.

The ancient river currents were strong enough to carry the eroded sand from the Appalachians out into the ancient sea as far south as present-day Miami. Further out than that, the sand that covered the ocean floor was not weathered quartzite, but calcium carbonate particles, made as waves and currents (and feeding fish) broke apart coral reefs and the shells of dead oysters and other sea creatures, and wore them down into tiny grains of sand. Unlike the light tan or pale brown quartzite sand, the calcium carbonate sediment was brilliant white, and would later become known by beachgoers as “sugar sand”.

By the time of the Miocene Era, about 25 million years ago, tectonic forces pushed Florida above sea level, and although sea levels would fluctuate up and down after that (making Florida either an island chain or a peninsula), parts of it would always remain above sea level. Florida’s modern coastline was formed about 10,000 years ago as the Ice Age ended and sea levels rose from the melted glaciers. The quartzite sand layers, once part of one of the mightiest mountain ranges in the world, now formed beaches along a new coastline–which are still here today.

Advertisements

Post a Comment

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Forgotten mysteries, oddities and unknown stories from history, nature and science.