Paper No. 6
Presentation Time: 8:00 AM-12:00 PM
TEMPESTITES FROM HURRICANE FRANCES IN THE BEACH AND LACUSTRINE ENVIRONMENTS ON SAN SALVADOR, BAHAMAS
Hurricane Frances hit the Bahamian island of San Salvador on September 2, 2004. Large storms and extreme events like the Category 3 Hurricane Frances cause an increase in wave base and the depth to which sediment is eroded and reworked across the bank. The associated storm surge can bring eroded reef fragments, sand, vegetative debris, human trash, and flotsam and jetsam landward. These deposits pile up in debris berms or rubble piles that, like a bathtub ring, map out the maximum height of the storm surge. The purpose of this research is to map and analyze the tempestites left by Hurricane Frances and to characterize the modern deposits and their distribution. Sites for study were chosen based on satellite imagery that appeared to show beach accretion and erosion. The study areas chosen (Salt Pond, The Thumb, French Bay, Pigeon Creek and Sandy Hook) are located on the southeastern section of San Salvador. We snorkeled along the southeast and south beaches to assess the condition of the coral reef. Large amounts of entangled plastic, debris and rope and some over turned coral were noted at the Thumb and French Bay beaches. The storm surge eroded the coastal sand dune adjacent to Salt Pond and deposited a blanket of sand into the lake that was covered by a post-storm algal mat. Four shallow hand-dug trenches and 7 short cores were collected on the exposed mudflat of Salt Pond in order to document the sedimentary structure of the storm surge washover deposits and frequency of washover events (storms) in the lake. The tempestite appears to be a layer of debris overlying layers of ripple-bedded sand. A study of the core stratigraphy is ongoing. Along the NW edge of Pigeon Creek, an inland lake with a tidal outlet, a deposit of organic debris at least 35 cm thick was deposited. Decomposition of the material has lead to an excellent medium for rooting coconut and seeds carried inland by the storm surge. At other locations, lone coconut trees, which are not native to the island, were found at high elevations along these beaches suggesting evidence of past storm deposits. Tempestites in the back beach environment are not likely to have a high preservation potential due to subsequent reworking. However, alternating layers of sand and organic mats suggest episodic storm deposits in the lacustrine environment.