The Role of Intense Storms on Backbarrier Morphodynamics: Examples From the New York/New Jersey Bight

Intense storms can significantly modify coastal landforms. Understanding the influence of these relatively rare, but potentially important, events on the evolution of coastal systems is important if we are to reliably forecast future changes. In the New York/New Jersey Bight the most intense storms are landfalling tropical cyclones that approach the region from the south. Since European settlement, four severe tropical cyclones, occurring in 1693, 1788, 1821, and 1893, have made landfall in the New York/New Jersey Bight. Each of these storms resulted in a rise in water level of over 2.5 meters above mean sea level (MSL) in New York City. Storm surges of this magnitude can overtop and breach barrier beaches creating inlets and depositing overwash deposits across the surface of backbarrier marshes. Severe winter storms, near miss, and minimal hurricanes impacting the region in the 20th century caused water levels to rise approximately 1.5-2 meters above MSL. Events of this magnitude likely caused erosion of the beach face, and limited overtopping and breaching restricted to areas with little or no dune development. Backbarrier sediments can preserve an archive of environmental changes. We collected a series of vibracores from four backbarrier marshes in the New York/New Jersey Bight. High-resolution grain-size and loss-on-ignition analyses were used to characterize the sediments and yield evidence of multiple storm-induced deposits. Heavy metal pollution horizons, pollen stratigraphic data, and C-14 ages were used to provide chronological control. In order to link the dynamics of the barriers with the sedimentary framework of the backbarrier estuary, we used ground-penetrating radar (GPR) to map the subsurface character of the barrier sediments. Our results indicate that intense tropical cyclones are very important in shaping the barrier and backbarrier environments in the New York/New Jersey Bight. Backbarrier and barrier sediments reveal records of overwash deposition and inlet formation associated with intense tropical cyclone landfalls. Evidence of three historic hurricane strikes in 1893, 1821, and 1693 has been recovered from the western Long Island sites. Only the 1821 hurricane is preserved in the recent sediments of Cheesequake, NJ. The age of many of the prehistoric storm-induced deposits among the four sites in the New York Bight overlap, suggesting that some of the overwash layers may have been deposited by the same prehistoric storms.