SANDY’S SANDS: HIGH-RESOLUTION SEDIMENTOLOGICAL INVESTIGATION OF HURRICANE SURGE DEPOSITS, MANTOLOKING, NEW JERSEY

A combination of geophysical (800 MHz georadar), sedimentological, and magnetic susceptibility (MS) analyses were used to examine a storm deposit five weeks following Hurricane Sandy (October 2012). Located 650 m south of the Mantoloking breach, the study site preserves a stratified sequence produced by storm surge deposition during spring high tide, both through a residential understructure and via two lateral scour channels. Because the sediment did not traverse (overwash) the entire barrier island, it represents an overtopping fan that would naturally contribute to barrier aggradation. The landward-sloping fan penetrated 55-75 m landward of the pre-storm foredune base, ranging between 0.3-0.5 m in thickness and containing a minimum of 120 m³ of sediment Geophysical images reveal landward-dipping reflections, with occasional discontinuities along bounding surfaces, which correspond to erosional truncations in trench exposures. Trench-wall casts capture 4-5 fining-upward sequences, grading from small pebbles to medium sand. Visually distinct heavy-mineral concentrations (HMCs) occur in 2-4-mm-thick laminations at the base of event beds and represent density lag generated during the waning stages of each surge event. HMC thickness and degree of concentration are likely a function of wave surge duration and magnitude, respectively. These mineralogical anomalies have bulk MS values exceeding 240 μSI, in contrast to <70 μSI for quartz-rich parts of the event bed. Therefore, textural parameters of each depositional interval must be combined with its MS properties to provide a more accurate representation of hydraulic equivalency. This study demonstrates the importance of considering particle density to reconstruct bed shear stresses generated by individual storm surge pulses.