INVESTIGATING BARRIER ISLAND MIGRATION AND STORM OVERWASH ON WALLOPS ISLAND, VA, THOUGH VIBRACORING

Wallops Island (WI) is a rapidly eroding barrier island located on the Eastern Shore of VA. Barrier islands migrate toward the mainland, or rollover, as a natural part of development. They are important coastline features because of the amount of protection they offer the mainland and estuarine environments. These islands are strongly affected by sea level rise (SLR) and are constantly being reshaped by currents and storm surge. Erosion and flooding related to SLR and storms cause difficulties for communities and facilities built on barrier islands. In light of recent and predicted future acceleration in SLR, it is important to understand the natural migration of barrier islands. Here we use core data collected by vibracore to investigate storm overwash and barrier island migration on WI.

We collected 4 cores, up to 2.5 meters in length, along a transect across WI from the modern dunes to the back bay salt marsh. We have extracted 8 samples of organic matter (e.g. shells, roots) for radiocarbon dating. Once we receive dates for these samples we can correlate the core data and aerial photographs to historic storm data. Cores from the seaward side of WI, extracted from modern and historic dunes, consist entirely of siliceous sands with evidence for frequent high water events (e.g. heavy mineral layers, organic detritus), cross-bedding, bioturbation, and stabilization by dune grasses. Cores taken from the back side of the island (phragmites stand-VC2, back bay salt marsh-VC1) show distinct changes in composition and lithology, ranging from back bay muds, to coarse sand, to organic-rich soils. Loss on Ignition (LOI) data for VC1 show layers with ≥75% organics at core depths of 0-5cm and 45cm which demonstrate periods of soil maturation and stabilization. LOI data also show silicate content >90% at depths 7-22cm and 51-95cm. We correlate massive sand layers without cross-bedding in VC2 and VC1 which we interpret to be evidence of storm overwash fans that transected the N portion of WI. Overall grain size is coarser in VC2 and the layer contains numerous shell fragments. Historical aerial photographs from NASA show evidence for large overwash deposits occurring pre-1938. Ultimately we hope to use these data, and deeper cores, to be able to calculate sedimentation and migration rates for WI.