Grain-size distribution and patterns in storm-induced event beds in a coastal pond

As coastal populations expand in size and build increasing infrastructure, they also become more vulnerable to the impacts of tropical cyclone events. The frequency of intense tropical cyclones, augmented by rising sea levels, is expected to increase over the next century, posing a greater threat of property damage and loss of life. The frequency of intense hurricane strikes is well characterized by sedimentary coastal archives at some locations, but the intensity of storms capable of producing these event beds is not well constrained. This study analyzes the grain-size distribution of major historic and prehistoric storm event beds along a transect of sediment cores from a kettle pond in Falmouth, MA. Reconstructions of intense-hurricane landfalls from this location identify a series of event beds spanning the past 2,000 years. The grain-size distribution of each event is determined using an image processing, size, and shape analyzer. Changes in grain-size distribution both spatially and temporally reveal characteristics of both storm intensity and the nature of sediment deposition. While many hurricane-induced overwash models assume a landward-fining pattern from the coastal barrier to the land, analysis reveals more complex sediment behaviors for some events, suggesting variation in both sediment source and suspension. Research into prehistoric intervals of increased frequency and/or intensity provides important insight into the current and future hurricane risks facing coastal communities in the northeastern United States.