What exactly are the Blowing Rocks?
Rock formations at Blowing Rocks Preserve are the largest of their type on the Atlantic coast.
This page was updated on August 19, 2020.
Winter storms and extreme high tides offer the best opportunities to see the TNC’s Blowing Rocks live up to their name. In a scene more reminiscent of Hawaii than Florida, waves surging against the craggy limestone shore can force geysers of water as high as 50 feet into the air.
Though the dark, jagged rocks do—at first glance—look like the remains of a misplaced lava flow, they are actually a specific type of sedimentary rock called Anastasia limestone.
Scientists disagree on exactly how far inland the limestone extends, exactly when it was formed (most likely around 125,000 years ago, in the Pleistocene Age) and whether it was formed by a single event or by multiple changes in sea level.
A few things scientists can agree on:
- Anastasia limestone extends along Florida’s coast from St. Augustine to Boca Raton, and
- Blowing Rocks Preserve harbors the largest outcropping on the U.S. Atlantic Coast.
The exposed rock at the preserve is unusual, not because Anastasia limestone is particularly rare, but because it is commonly found either underground or underwater.
Also known as coquina, from the Spanish for cockleshell, Anastasia limestone is composed primarily of shell and coral fragments, fossils and sand. Small fossils are clearly visible in the rock faces, most commonly the shells of small clams and oysters or pieces of a large snail called Busycon.
Why is so much of the limestone above ground at Blowing Rocks? No one knows. The land here might have once been part of an exposed sand ridge or the top of a reef, or for some other reason higher than surrounding areas.
At their height in winter, the Blowing Rocks are worth a visit in every season. The wind- and wave-carved limestone forms chimneys and shelves, burrows, blow holes and rocky pools. These offer great opportunities for exploration and imagination, as well as a rare window into Florida’s natural history.