Geology of a Swamp ...

Once upon a time, the Miocene Era (23 to 5 million years ago) to be specific, a layer of clay was laid on the ground during a time when the climate was warmer. It is this layer of clay, called the Hawthorne Formation, that has made the ground impermeable – bucket like, the reason why water in the swamp doesn’t just disappear into the ground. The Hawthorne Formation is a name for layers of coastal sedimentary rock that have similar features.  Later, during the Pliocene era ( 5 to 2.5 million years ago) as ocean levels rose and fell, remnants of barrier islands and coastal bays were left behind. The Okefenokee basin is an archaic coastal bay, defined on the eastern side by an equally archaic barrier island which acts like a dam and holds the rainwater in place. The modern wetland itself began to form during the late Holocene (12,000 years ago to the present) when the climate warmed and plant-life once again began to thrive.

Uplands to the West, ridge to the East

So you can look at it this way: Imagine a clay bowl that was flooded by rising sea levels where barrier islands (like Assateague Island, where Ocean City, MD is located) were established with coastal bays behind them – just like in modern times. As the climate cooled and the sea levels dropped a series of ridges with basins behind them were left behind.  So the eastern edge of the Okefenokee Swamp is defined by an old barrier island, called Trail Ridge, and to the west of this ridge is the basin, now filled with rainwater and called the Okefenokee Swamp.  You can imagine how the swamp has grown over time as sediments began to fill the basin, displacing and raising the water level. The water would over flow and spread out over an even greater area! So today we can find on the eastern part of the swamp the oldest, deepest part of the basin where the open water wet prairies and floating islands of accumulated peat are located and as we move west and upland we find flooded forests. (Flooded later as the basin filled with sediment and the water level rose!)

It can be hard to imagine our Earth as a constantly changing little blue ball. The change is slow, imperceptible in our lifetimes – with the possible exception of global climate change – but is taking place none the less. It is a perpetually unfolding story that we are only beginning to understand.