Sedimentary record of storm deposits from Hurricane Ike, Galveston and San Luis Islands, Texas

Prehistoric records of land-falling tropical cyclones further our understanding of the spatial and temporal variability of tropical cyclone activity and its relationship with global climatic changes. Here, we describe deposit stratigraphy and sedimentology resulting from overwash during Hurricane Ike, which made landfall on September 13th 2008, to provide a much needed modern analogue for paleo-hurricane deposits and evaluate the hurricane's influence on barrier stability. We compared the volume, grain size distribution, organic content and foraminiferal assemblages of washover deposits at three sites from Galveston and San Luis Islands, Texas that were up to 50km west of Ike's landfall. Storm surge heights varied between 3.7 and 2.7m with inland inundation extents of 330 to 113m. At each of the study sites, Hurricane Ike eroded the shoreline and re-deposited a landward-thinning sand sheet between 0.02 and 0.28m thick over short-grass prairie/salt-marsh soil. Shoreline erosion estimates suggest that only between 10 and 30% of eroded beach sediment is deposited on land as washover (net gain to barrier elevation), while the remainder is re-deposited subtidally or offshore, a potential net loss to the coastal sediment budget. The washover sediment was readily identifiable by abrupt changes in grain size, organic content, and buried in situ grasses. Foraminiferal assemblages within washover and short-grass prairie/salt-marsh sediments (when present) have similar assemblages, which are dominated by Ammonia spp. and Elphidium spp. These species are common to bay and nearshore environments of the Gulf of Mexico. Foraminiferal species Bolivina subaenariensis, Quinqueloculina seminulum and planktonic species are restricted to the washover deposits, which may suggest sediment provenance from inner shelf environments.