SPIT ELONGATION AS A CONTROL ON DOWNDRIFT BARRIER-ISLAND STABILITY- INSIGHTS FROM ASSATEAGUE ISLAND, VA

Interactions among antecedent geology, changing sea level, and the physical processes (waves, tides, currents) responsible for sediment transport along and across the coastal zone create imbalances in accommodation creation and filling. In response, coastal change occurs through processes such as beach erosion or progradation, barrier-island breaching or migration, and spit truncation or elongation. The latter largely reflects sediment trapping associated with long- and cross- shore sediment fluxes at the downdrift terminus of sedimentary coastal landforms. In northern Virginia (U.S. East Coast), elongation of Fishing Point, the southern spit-end of Assateague Island, plays a complicated but central role in regional sediment transport. A series of seven sediment cores (20–25 m deep), combined with detailed GIS mapping of historical paleo-shorelines and detailed grain-size analysis, reveals that growth of this spit has trapped nearly 50 x 10⁶ m³ during just the last 100 years. Our results demonstrate the linear volumetric and areal growth of Fishing Point through time and present the first detailed stratigraphy for, and insight into the underlying geology of, one of the largest historic accretionary landforms on the U.S. East Coast. We find that sand trapping at Fishing Point has reduced longshore transport fluxes by at least 25%, and likely contributed to the erosion and/or landward migration of adjacent, downdrift barrier islands. Thus, our findings demonstrate the potential for longshore sediment trapping through natural growth of updrift sediment sinks to control long-term and large-scale downdrift coastal behavior.