By Thomas Ambrose
On the shore of Florida’s Gulf Coast, the islands of Captiva, Sanibel and Fort Myers Beach all have very low elevations, rich in sand and no rock outcrops. The area of Gulf Ridge on Sanibel is only 3 feet above sea level and they call it a “ridge.”
Typical of these islands is very shallow water offshore — a mile out from Fort Myers Beach is only some 10 feet deep. During storms, wind can quickly push water ashore as a “sea surge,” so this may be why Fort Myers Beach and other Gulf Coast islands got hit hard by recent hurricanes.
On Google Earth I recently checked ocean water depths off Ocean Ridge to Delray Beach, which range from 100 to 150 feet about a mile offshore.
Island elevations from 2 feet along the Intracoastal Waterway to 23 feet on the coastal ridge in Ocean Ridge should give added protection in a storm. Maybe more important is that islands along the Palm Beach County coast exhibit outcrops of hard, indurated and bedded sedimentary rocks which form a solid foundation for overlying buildings in rising waters.
Across the intracoastal in Boynton Beach, ancient sand dunes and rock ridges rise to some 34 feet in elevation between Seacrest Boulevard and Interstate 95 — something never to be found on the unstable sand island along the Florida Gulf Coast.
Aren’t we lucky!
Thomas Ambrose received a bachelor’s from the University of Oklahoma and a master’s from Rutgers in geology after serving in WWII. As a global oil exploration geologist, he has lived in eight countries (six of them island nations) and visited 128. He has lived in Ocean Ridge since 1991.
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