Highlights • A new, detailed evolutionary model for the longest barrier in the Gulf of Maine and n updated chronologic framework for Holocene sea-level change and barrier development in northern Massachusetts are presented. • Spit elongation accounts for more than 60% of the barrier length • Shoreline progradation accounts for more than 90% of the barrier width • A paleo-inlet was active in central Plum Island around 3.5-3.6 ka. • Inlet closure occurred due to backbarrier infilling and tidal prism reduction.

Coastal barriers are particularly susceptible to the predicted effects of accelerated of sea-level rise and the potential for increased impacts of intense storms. Over centennial scales, barriers are maintained via overtopping during storms, causing deposition of washover fans on their landward sides. This study examines three washover fans on the south shore of Martha's Vineyard using a suite of data including vibracores, ground penetrating radar, high resolution dGPS, and LiDAR data. From these data, the volumes of the deposits were determined and range from 2.1-2.4 x 10 4 M .Two overwashes occurred during Hurricane Bob in 1991. The water levels produced by this storm have a return interval of ~28 years, resulting in an onshore sediment flux of 2.4-3.4 m 3 /m/yr. The third washover was deposited by a nor'easter in January 1997, which has a water level return interval of ~6 years, resulting in a flux of 8.5 m 3 /m/yr. These fluxes are smaller than the flux of sediment needed to maintain a geometrically stable barrier estimated from shoreline retreat rates, suggesting that the barrier is not in long-term equilibrium, a result supported by the thinning of the barrier over this time interval.

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Coastal barriers are particularly susceptible to the predicted effects of accelerated of sea-level rise and the potential for increased impacts of intense storms. Over centennial scales, barriers are maintained via overtopping during storms, causing deposition of washover fans on their landward sides. This study examines three washover fans on the south shore of Martha's Vineyard using a suite of data including vibracores, ground penetrating radar, high resolution dGPS, and LiDAR data. From these data, the volumes of the deposits were determined and range from 2.1-2.4 x 10 4 m 3 . Two overwashes occurred during Hurricane Bob in 1991. The water levels produced by this storm have a return interval of ~28 years, resulting in an onshore sediment flux of 2.4-3.4 m 3 /m/yr. The third washover was deposited by a nor'easter in January 1997, which has a water level return interval of ~6 years, resulting in a flux of 8.5 m 3 /m/yr. These fluxes are smaller than the flux of sediment needed to maintain a geometrically stable barrier estimated from shoreline retreat rates, suggesting that the barrier is not in long-term equilibrium, a result supported by the thinning of the barrier over this time interval.