DECADAL CHANGES IN BARRIER ISLAND FACIES NEAR MANSFIELD PASS ON PADRE ISLAND, TEXAS FROM 1950-PRESENT

Barrier islands serve an important role in shielding coastal areas from storms and wave erosion. Monitoring changes in the barrier island system helps understand the effect of storms and sea level rise on the stability of the island. Here, we use aerial and satellite images from 1970-2020 to examine changes in Padre Island, TX. Georeferenced images were used to generate geologic surface maps of a 57 sqkm area. Mapped surface geology includes the beach, dune ridge, coppice dunes, washover channels, washover fans and deflation flats, vegetation-stabilized dunes, back-island sand flat, back-island dune field, wind-tidal flat, lagoon-margin sand, and ephemeral water. Qualitative assessment of the images reveal that this area experienced significant change over the past five decades from unvegetated dune fields to expansive microbial mats and vegetated dunes. Quantitative mapping shows a reduction of 89.8% in the back-island sand flat and 53.6% in the back-island dune field while also showing a growth of 704.3% in vegetation-stabilized dunes, 136.6% in wind-tidal flats, and 102.4% in lagoon-margin sand. Total subaerial surface area has shrunk by 8.4%. Extensive microbial mats, primarily mapped within the wind-tidal flat and lagoon-margin sand, have developed on the lagoon-facing back island region and in low lying washover fan and interdune areas. Such expansive microbial mats are an atypical feature of the back barrier. Possible triggers for the transition from active sand dune fields to microbial mats and vegetation may be modifications to the island topography post-hurricane Allen in 1980 and a sea-level driven water table rise. The mats may signal an out-of-equilibrium island in adjustment to changes in sea level and storm influence. Further study using aerial images and in-situ data will provide further insights on the role of microbial mats in barrier island stability.