Geologic History, Depostional Envirnoment, Processes, and Hydology of Galveston Island, Texas

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Galveston Island is a very young geologic feature compared to the Earth's age of approximately 4.5 billion years. Estimates suggest that Galveston Island and other Texas barrier islands began forming as submerged bars no more than 4,500 to 5,500 years ago, based on radiocarbon dating of shells (Fisk, 1959). The following descriptions of development history, present shoreline conditions, and processes and environments have been modified from various sources including LeBlanc and Hodgson (1959), Bernard and others (1970), Fisher and others (1972), Morton (1974), McGowen and others (1977), Weise and White (1980), and Paine and Barton (1989).

The origin of barrier islands has been the subject of debate, with different processes or combinations of processes shaping and modifying them. These processes depend on variables such as sediment source, type, and supply, rate and direction of relative sea-level changes, basin shape, continental shelf slope, currents, waves, and tides. Three of the most discussed theories of barrier-island origin include development from an offshore shoal or submerged sandbar, development by spit accretion resulting from longshore drift, and development by drowning of the area landward of mainland beach sand ridges (Wanless, 1974).

One possible explanation for the origin of Galveston Island is that it developed from offshore shoals, with later growth aided by spit accretion. The offshore shoals might have originally been mainland beach ridges submerged during a rise in sea level. All three processes may have played a role in the island's origin, with different segments of the island undergoing different processes at varying rates during their development.


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