Paper No. 10
Presentation Time: 4:25 PM

UPPER TEXAS COAST UNPRECEDENTED EROSION: INTENSE HURRICANE IMPACTS AND ACCELERATED SEA-LEVEL RISE RESPONSE


ANDERSON, John B., Department of Earth Science, Rice University, 6100 Main Street, Houston, TX 77005 and WALLACE, Davin J., Department of Marine Science, The University of Southern Mississippi, Stennis Space Center, MS 39529, johna@rice.edu

Current rates of barrier migration along the upper Texas coast are unsustainable given the age of the barriers. By quantifying long-term sand accumulation offshore and in San Luis Pass Tidal Delta, we can compare long-term and short-term erosion of Galveston Island. Currently, the only source of sand into these locations is erosion of Galveston Island itself. The average hurricane-related offshore sand flux from ~5,142 yr B.P. to present was ~4,306 ± 673 m3/yr, with a decrease in this sand flux from ~2,692 yr B.P. -present to ~931 ± 271 m3/yr. San Luis Pass Tidal delta formed ~2,100 yr B.P., when the rate of sea-level rise began to decelerate from ~2.0 mm/yr to ~0.6 mm/yr. We quantify additional sand eroded from Galveston Island between ~2,100-200 yr B.P. to be ~4,700 m3/yr based on deposition into San Luis Pass Tidal Delta. Compared to modern rates of change, this erosion appears to have increased to ~10,000 m3/yr over the past ~200 years based on historic navigational charts and sediment cores. A summation of these volumetric fluxes together with published sand fluxes to the Galveston Island shoreface environment equals a total of ~130,361 ± 28,271 m3/yr. This value is considerably lower than the ~215,000 ± 48,000 m3/yr that would have been produced from an equilibrium profile shift associated with the measured historic erosion rates. This unprecedented erosion is associated with the recent accelerated sea-level rise and coupled constant hurricane impacts, with only a minor signal from anthropogenic influences.