Slide Barrier Island

Pensacola Beach Sunrise © Harry Purcell

BARRIER ISLAND FORMATION

The geography of barrier islands changes every single day. Our sparkling white quartz sand originated in the Appalachian Mountains—as the mountains have eroded over millennia, quartz has been broken down and transported via rivers into the Gulf. This sediment is deposited in a delta at the mouth of the river, becoming a sand source for incoming currents and catalyst for the transport of sand parallel to coastal shores. Offshore sand is regularly brought in on waves and deposited on the beach, where wind brings it onshore. Beaches typically grow in the spring and summer as gentler waves bring this sand in. During the winter, more energetic waves erode the sand from the beach and take it offshore.

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Primary Dune

In the northern Gulf, the current and longshore drift move sand from easterly islands and transport it west. A quick satellite image search bears that out, as you’ll see islands from St. George Island, Florida all the way to Ship Island, Mississippi taper from the east and stretch longer to the west side where sand is deposited.  Shifting sands are transported by wind, waves, and even humans, reshaping the beachfront every hour.

 

Major disturbances, such as tropical storms, hurricanes, and construction, can also change islands’ shape. Many storms have washed sand over the islands so the leeward (inland) side grows, while other times entire islands may be cut into two or three pieces.

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Tree Stumps Indicate Changing Shoreline

Barrier islands may form in one of several ways. Some are ancient dune ridges that were present during the last ice age, but after the ice caps melted the land around them flooded and the ridge became an island. Vegetation took root, and the island stabilized. Some barrier islands are sand bars that have accumulated large amounts of sand and rolled closer to shore, eventually reaching a shallow bottom and moving above water. “Spit” islands are common, being fingerlike stretches of sand that build out from the mouth of a bay or other estuary as the currents move sand along the coast. Based on the shape and formation of Santa Rosa Island, historians and geographers believe our beach formed as a “spit” island from the mouth of Choctawhatchee Bay in Okaloosa County, where the island begins.

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Wind Sculpted Sand Dunes

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