tbo: Tampa Bay Online.
Tuesday, Apr 24, 2018
  • Home
Commentary

Why Texas beaches look different

There's been a lot of talk recently about how oil drilling has made the Texas and Louisiana coast look dirty. West Florida beaches are blessed with especially clean sugar-white sand. Louisiana and Texas are not so blessed. There is a good reason for the difference. It's all about geology, wind, and tides - not oil drilling. Not all sand is created equal. The sugar-like beach sands east of the Mississippi River have a distinctly different source than sands in Louisiana and Texas.
Over millions of years, quartz has been weathered from granite in the Appalachian Mountains - the source of our white West Coast sand. That sand took a southward route after emerging from rivers and streams like the Suwannee and Apalachicola. Louisiana and Texas are another matter. Most of their sands came from the U.S. heartland via the mighty, and muddy, Mississippi River. Their sands were washed from the gooey brown clay that is the Mississippi Delta. Sand from the heartland sands also contains quartz along with dark-colored mineral grains, charcoal, and other organic matter. The difference in source and impedance effect of the Mississippi Delta are the major reasons we have white sugar-like sand beaches while Texas and Louisiana have sand that looks more like brown sugar. The color of Texas and Louisiana sands has nothing to do with offshore drilling. Another factor is the miles and miles of muddy soft sediment off Texas and Louisiana. Storms stir that sediment into suspension, making beach water look like cafe-au-lait. Off west Florida, we have more than 100 miles of hard limestone and far less sediment to stir up. Even farther out into the Gulf, the limestone shelf drops abruptly into a totally different environment, the deep Gulf. A gigantic blanket of thick salt underlies the deep Gulf. These vastly different terrains, created when dinosaurs roamed the Earth, were formed during the breakup of the giant continent that shaped the Americas, Africa, and the Atlantic Ocean. Under the weight of mud and sand, salt under the deep Gulf is constantly being squeezed upward like thick molasses. Salt movement is slow but relentless, creating underwater hills and valleys that geologists call salt domes. Salt domes form an almost impenetrable seal that can trap oil and gas. These features also tend to leak some of the oil and gas as hydrocarbons slowly ooze upward. So, what does this geological information have to do with our decision to drill or not to drill? First, the decision makers need to know that at least 99 percent of all oil in the oceans originates from a combination of tankers and cargo-ship bilges, tanker accidents (like the one we had in Tampa Bay in 1993), natural seeps, and runoff from land. As the debate over oil drilling heats up, policymakers should ignore the wives' tale that Texas and Louisiana sands look different because of the oil and gas industry. Science provides us with the truth.

Dr. E.A. Shinn is a professor of marine science at the University of South Florida.

Weather Center
Comments