For those who want to know more about Sea Rise, follow the March Meeting of the geological Society of America |
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Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)
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THE SEA ALSO RISES |
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| PILKEY, Orrin H., Earth and Ocean Sciences, Duke University, Nicholas School of the Environment, P.O. Box 90228, Durham, NC 27708, opilkey@duke.edu and YOUNG, Rob, Program for the Study of Developed Shorelines, Western Carolina University, Belk 207, Cullowhee, NC 28723A number of state and local science panels have predicted that the global sea level will rise by 1 to 2 m by 2100. The behavior of the Greenland and West Antarctic ice sheets in the last decade would indicate that a 1 m sea level rise should be viewed as minimal. Adding to the problem is the first recognition (in 2009) of a significant contribution of meltwater from the East Antarctic ice sheet. The dire predictions seem to have had little impact on coastal zone management so far, perhaps because they are not recognized as dire and the ramifications are not widely understood. In fact, the ramifications have not been laid out for the public as yet, a public that in significant part is not convinced that global warming is even occurring.
A one meter sea level rise will end barrier island development along America’s 5600 km long barrier island shoreline – the longest in the world. At the new sea level, shoreline erosion will be unstoppable except by construction of seawalls that must completely surround the islands. At the same time that the barrier islands are facing their crisis, the cities will also be in trouble, and it is likely that preservation of Miami, Manhattan and Boston will trump funding for barrier island communities. The time for societal action is now because building practices and infrastructure emplacement today will have an impact on the sea level response of tomorrow. The single most important response would be prohibition of high-rise buildings near the shoreline. On barrier islands this response must be flexible if the islands are to survive. Creative and even unthinkable approaches are needed, including perhaps artificial migration of heavily developed islands and eventual wholesale destruction of buildings along densely populated shorelines like those on the Florida Peninsula. It is important for coastal geologists to get involved in this public debate because no one else understands what a 1 m sea level rise will do on a barrier island shoreline! |
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HOLOCENE GEOLOGIC DEVELOPMENT OF THE CAPE HATTERAS REGION, OUTER BANKS, NORTH CAROLINAMCDOWELL, Katie1, MALLINSON, David2, CULVER, Stephen2, and WALSH, J.P.3, (1) Department of Geosciences and NRM, Western Carolina University, Cullowhee, NC 28723, kmcdowell@wcu.edu, (2) Department of Geological Sciences, East Carolina University, Greenville, NC 27858, (3) Geology, Greenville, NC 27858The late Holocene evolution of the Hatteras Flats and Buxton beach ridges was reconstructed using sedimentological, micropaleontological, geophysical and chronostratigraphic data. Sixteen vibracores were collected from the Hatteras Flats and seven geoprobe cores were collected from the Buxton beach ridges. Geophysical data (ground penetrating radar and seismic surveys) were obtained throughout the study area to aid in paleoenvironmental reconstructions. Using ten lithofacies, five foraminiferal biofacies and geophysical data, five environmental facies were distinguished: low salinity estuary, high salinity estuary, normal marine salinity/flood tidal delta/submarine shoal, normal marine salinity/flood tidal delta/beachface and barrier island sand. Thick sequences of normal marine salinity deposits comprised of foraminiferal species such as Hanzawaia strattoni, Quinqueloculina seminula and Eponides repandus were present in all sixteen vibracores between 1.5 and 8.5 m below MSL. These data indicate that normal marine salinity conditions occurred over the Hatteras Flats in the study area approximately 1,100 yrs BP. Five optically stimulated luminescence (OSL) dates within normal marine salinity units gave age estimates ranging from 1,420 to 1,060 yrs BP, corresponding with a previously documented barrier island collapse in the southern Outer Banks. Hatteras Island was likely reduced in size by erosion of the beach ridges and the creation of large gaps in the barrier islands between Buxton and Hatteras Village and between Buxton and Avon. These conditions resulted in open bay environments on the Hatteras Flats. An OSL age estimate of 675 ± 180 yrs BP within this normal marine salinity unit indicates that marine water influenced the central Hatteras Flats for several hundred years. By 500 yrs BP, it is likely that the simple barrier islands near Cape Hatteras had reformed, returning estuarine conditions to the Hatteras Flats. An OSL age estimate indicates that an inlet was present between Cape Hatteras and Avon 375 ± 60 yrs BP. GEOMORPHIC LINKAGES BETWEEN TRANSGRESSING SIMPLE BARRIER ISLANDS AND BACK-BARRIER FLATS IN RESPONSE TO CLIMATE CHANGE, NORTH CAROLINA OUTER BANKSRIGGS, Stanley R., AMES, Dorothea V., MALLINSON, David J., CULVER, Stephen J., and PARHAM, Peter R., Department of Geological Sciences, East Carolina University, Greenville, NC 27858, riggss@ecu.eduBarrier island segments within North Carolina’s Outer Banks are divided into two geomorphic types: simple and complex based upon the sediment supply, physical dynamics, and evolutionary history of the islands. Simple island segments are sediment poor resulting in low and narrow barriers dominated by storm-driven interaction between inlet flood-tide deltas (FTDs) and over-wash ramps (OWRs). About 75% of the 280 km-long Outer Banks are simple barrier islands with all geomorphic elements having formed within the last 500 years. Sediment-rich complex barrier islands are high and wide due to substantial sediment input during their evolutionary history. They are characterized by a modern beach that has welded onto an older barrier island segment. The older segments are dominated by multiple sets of beach ridges and back-barrier dune fields that date from about 3,000 years ago to the present. Since most complex islands have little potential for the formation of inlets and/or oceanic overwash, salt influence is minimized allowing for development of extensive maritime forests. The dominance of transgressive simple barrier islands on the Outer Banks has resulted in the deposition of a broad (1.5 to 8 km wide) and shallow (<1 m deep) back-barrier shoal system known as Hatteras Flats. This shoal system consists of submerged paleo-FTDs and associated tidal channels that are being buried along the barrier island side by OWRs of the transgressing islands. OWR-dominated barrier islands slope from the island berm downward to the back-barrier estuarine shoreline. Lower portions of the OWR grade from the supra-tidal zone dominated by microbial mats and/or interior marshes, to the inter-tidal zone dominated by salt marshes. The shore-parallel, back-barrier platform marshes are split by tidal channels to form the classic molar-tooth structures. The back-barrier platform marshes transition into the Hatteras Flats where the sub-tidal estuarine zone is bound by microbial mats and the shallow submarine estuarine zone is dominated by submerged aquatic vegetation. Thus, the FTD-dominated Hatteras Flats form a stabilized shallow base that is the future foundation upon which the sub-aerial portion of the barrier island will migrate onto as sea-level rise and ocean shoreline recession continues. |
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outerbanksharvest
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