HR: 0800h
AN: H41C-0304    [Abstracts]
TI: Sedimentary archives of extreme flooding events in the Northeastern Caribbean
AU: * Woodruff, J D
EM: jwoodruff@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AU: Donnelly, J P
EM: jdonnelly@whoi.edu
AF: Woods Hole Oceanographic Institution, Department of Geology and Geophysics, Woods Hole, MA 02543 United States
AU: Scileppi, E
EM: Elyse_Scileppi@brown.edu
AF: Brown University, Department of Geology, Providence, RI 02912 United States
AB: Flooding associated with both hurricanes and tsunamis can be extremely hazardous to coastal communities. Accurately reconstructing the past history and intensity of these extreme events is valuable when assessing future risks to specific coastal regions. Overwash deposits preserved within backbarrier lagoons and salt ponds can provide a means for documenting previous flooding activity; however, the details of how these individual flooding events are recorded within these environments is still not completely understood. An analysis of sediment cores collected from a lagoon system in the Northeastern Caribbean (Laguna Playa Grande, Vieques, Puerto Rico) reveal coarse-grained deposits interlaminated within fine-grain lagoon sediments. These coarse-grained laminae consist of beach and nearshore sediments and can be mapped across the lagoon. These coarse-grained strata are likely overwash deposits that may provide a high-resolution record of extreme flooding events in the region over the last 5000 years. Understanding the sedimentary record of historical events of known intensity and duration is necessary, however, in order to make inferences about the cause of prehistoric coarse-grained layers. Vieques has experienced relatively little coastal development and contains a well documented history of storm and tsunami activity since its colonization in the 16th century. The island thus provides an excellent opportunity to study how recent extreme flooding events have been preserved in a natural lagoon system. Overwash deposits preserved at Laguna Playa Grande over the last 200 years are analyzed in order to identify which historically documented flooding events appear to have left a sedimentological record. These deposits are initially identified based on high resolution grain-size analysis and x-radiographic imaging. Activity levels for Pb-210 and C-137 are measured to date recent sediments (over the past 200 yrs) and to link individual coarse-grained strata with documented flooding events. Radiocarbon methods are used to date the age of sediments on the 100-1000 year time scale. Diatomic assemblage distributions and chemical compositions within deposits (percent calcium carbonate, siliciclastic, and organics) are analyzed to identify source areas for specific sedimentary units. The grain-size distributions within flood deposits are also analyzed in order to develop methods for quantifying the wave and currents conditions present during times of mobilization and deposition. Results from this study show that documented hurricane and tsunami events in the Northeast Caribbean are recorded within the sediment stratigraphy at Laguna Playa Grande. These findings emphasize the accuracy to which lagoon systems can record extreme flooding events and helps to validate using sediment cores from these environments to construct a high-resolution, prehistoric record of tropical cyclone and tsunami activity for the region.
DE: 3374 Tropical meteorology
DE: 4546 Nearshore processes
DE: 4564 Tsunamis and storm surges
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3022 Marine sediments--processes and transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting