RECOGNIZING PAST STORM EVENTS RECORDED IN SEDIMENT CORES BASED ON ANALYSIS OF RECENT OVERWASH LOBES DEPOSITED BY SUPERSTORM SANDY

The storm surge from superstorm Sandy breached the dune line and deposited prominent lobes of sand into the marshes and bays of Long Island’s southern barrier islands. Five sediment cores from two overwash lobes were collected west of Shinnecock Inlet in the vicinity of Tiana Beach, near Hampton Bays, New York to study the sedimentology and structure of hurricane overwash deposits. Analysis of these cores reveals that overwash sands vary in their sedimentological characteristics depending on their location relative to the margin of the lobe and stratigraphic position within the lobe deposits. Storm overwash sediments deposited subaerially directly on the marsh surface are relatively homogeneous while subaqueous sands deposited directly into the bay show heavy mineral laminations due to settling and or reworking during lobe deposition. The grain size distribution of Sandy overwash closely matches that of dune sands collected nearby and differs from more coarse-grained foreshore, berm and backshore beach sands. Overwash sediments are relatively fine-grained (medium-fine sand, mean phi size 1.75) and lacking in coarse sand to pebble-sized material. They show a tendency to coarsen upward from the base to the top of the lobe, perhaps due to the increasing incorporation of beach sand into the overwash as the lobe develops. Sand layers in sediment cores collected in the same area as the superstorm Sandy overwash deposits can be ascribed to past storms (1938, 1954 hurricanes, 1962 nor’easter) based on analysis of historical aerial photos taken after major storm events. These older sand layers exhibit sedimentological characteristics similar to those observed in the modern Sandy overwash, confirming their identity as storm generated layers.