EVIDENCE OF ACCELERATED COASTAL CHANGE ALONG THE TEXAS COAST

With the well-documented acceleration of sea-level rise and the potential increasing frequency of hurricane strikes over historical time, erosion along the Gulf of Mexico is expected to be dramatic. However, there is a lack of quantitative field-based studies to document how coastal evolution in the geologic past compares to the historic record. Here, we relate changes in the sand flux of a tidal delta to barrier island erosion. Tidal inlets sequester sand from longshore currents, and can record changes on adjacent barrier islands. Most tidal inlets and deltas along the Gulf of Mexico coast have been anthropogenically modified, therefore making it difficult to directly compare natural versus man-induced changes. However, San Luis Pass along the upper Texas coast has remained entirely natural, therefore presenting the unique opportunity to study the response of Galveston Island to global change over both geologic and historic time. By constraining relative sea-level rise (subsidence and eustasy), sediment supply variations, and hurricane impacts, we assess the influence of these forcing mechanisms on coastal change. We determine that the tidal inlet and delta did not form until ~2,100 yr B.P., coinciding with a sea-level rise deceleration from 2.0 mm/yr to 0.60 mm/yr. Over the past ~200 years, the sand flux into San Luis Pass has more than doubled relative to the geologic past. This sand is derived from erosion of Galveston Island, meaning that erosion of this barrier has increased in recent time. These changes are associated with the recent relative sea-level rise acceleration and/or increased hurricane frequency, and are expected to represent the response of similar barriers along the Gulf of Mexico coast.