![]() However, wind tides occur when strong steady winds elevate the water’s surface. The astronomical tidal range in the Laguna Madre is even smaller than that of the Gulf. The Texas Gulf Coast has a uniformly small tidal range. Storms and high tides cut into these dunes, abruptly changing the contours of the island. The fore-island dune ridge traps additional sand and prevents it from migrating back to the sea. Plants stabilize the sand with roots and spreading vines, forming a relatively continuous dune ridge. This migrating sand is trapped along the back edge of the beach by salt-tolerant grasses and flowering plants. Sediments deposited high on the beach are dried and transported landward by persistent onshore winds. The Gulf beach is a complex environment where water and air interact and compete for sediments. Swash bars and berms are beach deposits formed as a result of this wave action. Flat waves and smooth, round, symmetrical waves transport sand to the beach. They agitate the water and suspend sand so that they erode and destroy, or deposit and construct as applicable. On North Padre Island, Gulf waves break on the upper shoreface, especially during fall and winter. The sand is then accumulated in dunes which may become stabilized by vegetation or are driven into the Laguna Madre. Winds blow away the sand, leaving the exposed shells behind. Because the currents converge at this point, a good number of large and small shells are deposited on the beach. This convergence point is where longshore currents moving north to south and currents moving south to north meet. Little and Big Shell Beaches are located near the (27 degree North latitude) convergence point. Man-made jetties perpendicular to the Gulf shoreline interfere with longshore sediment transport these occur at Mansfield Channel, Mustang island, and Water Exchange Pass. The converging currents deposit sands from the Rio Grande, Colorado, Brazos and Mississippi Rivers (the sands show traces of magnetite, garnet, zircon, tourmaline, quartz, and other sediments identified from these rivers). These ocean currents converge at 27 degrees North latitude, although winds shift somewhat during the year. Today, hurricane washovers and wind-carried sand deposited in the Laguna Madre build Padre Island’s landward side at the expense of the Laguna Madre.Īlong Padre Island’s northern half, northeast winds drive longshore currents and along Padre’s southern half, southeast winds drive longshore currents. All of Padre Island will probably retreat landward through long-term erosion due to the following causes: (1) interruption and decrease in sediment supply, (2) relative sea level rise, and (3) tropical storm activity. South Padre Island has been in a destructive phase for a long time, probably having retreated landward (along with the lagoon and mainland shoreline). Wind, wave and current action continue to rework and shape the island. The northern half of Padre Island’s shoreline is in equilibrium the southern half (and much of the remaining Texas coastline) is in an erosional stage. Padre Island graphically illustrates the life and sequences of a barrier shoreline: accretionary or building phase, equilibrium or stability phase, and erosion or destructional state. (A spit is a long, narrow tongue of sand extending from a mainland shoreline and formed by the shoreline drifting of sediments.) After a history of shifting, abandonment, and reestablishment by storm breaches, many tidal inlets were slowly closed and short islands were joined to form today’s longer islands. It is theorized that Padre Island formed from offshore shoals with later growth aided by spit accretion. ![]() ![]() Barrier island origins have been debated for many years by geologists, but it is agreed they are formed and modified by such factors as sediment type and supply, sea-level directional changes, current and wave strength and direction, and tide magnitude. ![]() Geologic speculation indicates the emerged island itself may be 1,000 to 1,500 years younger. Padre Island began forming as a submerged sand bar some 4,500 years ago, as shown by radiocarbon dating of shells. These natural barrier islands act to protect the mainland from the direct onslaught of storms. It is one of 300 hundred islands stretching from Maine to Mexico. Geologically speaking, Padre Island is a young island. This small channel, which existed for only a few months around 2002-2003, illustrates the ephemeral nature of a barrier island.
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