Date of Award
Master of Science in Oceanography
Located along the Mid-Atlantic coast of the United States, the state of Delaware is vulnerable to both tropical storms tracking from the warmer water of the southern Atlantic Ocean as well as strong extratropical storms, such as nor' easters, that are more common in the northern Atlantic. Although no hurricane has made direct landfall over Delaware in the past 200+ years of historical record keeping, several have passed with enough proximity to cause significant damage and erosion throughout the state's coastal communities. Effects from the Ash Wednesday Storm of 1962, which inflicted widespread flooding and destruction across coastal Delaware, indicate that extratropical storms are an equal threat for this stretch of Atlantic coastline. In order to better characterize the frequency of similar intense storm impacts throughout Delaware's history, five sediment cores were retrieved from Silver Lake, a small body of freshwater located in the coastal town of Rehoboth Beach. Separated from the Atlantic Ocean by a ~200 meter wide coastal barrier, Silver Lake is susceptible to overwash processes resulting from intense storm systems that track over or near the area. Preserved as thin veneers of sand within otherwise fine-grained mud and silt-sized sediment, these layers of washover preserve a record of past storms strong enough to transport sand into the back-barrier lake environment. Sedimentological and mineral magnetic properties suggest that storm surges have, on multiple occasions, formed temporary inlets through the barrier fronting Silver Lake in the past ~500 years. As such, core sediments have alternating facies indicative of low-energy lake-bottom and saltwater marsh deposition. Despite this environmental variability, storm signals are preserved throughout both facies, and likely represent the most severe storm events impacting the Silver Lake area. Stratigraphic and geochronological analyses of sediment cores suggest that approximately eight storms have deposited washover sand into Silver Lake during the past ~500 years. Several of these storms likely occurred in the midst of cooler Atlantic Ocean sea surface temperatures during the Little Ice Age (~ 1550-1850 A.D.), suggesting that the frequency of intense storm events in Delaware is not controlled by changes in sea surface temperature. Additional first-order comparisons of the storm record with changing phases of the Atlantic Multidecadal Oscillation, the North Atlantic Oscillation, and the El Nino/Southern Oscillation also failed to indicate any possible correlations. However, spectral analysis suggests that the periodicity of mean grain size in Silver Lake may be influenced by the alternating positive and negative phases of the North Atlantic Oscillation. Apart from mean grain size, the record of overwash deposition is likely dominated by individual storm characteristics and pre-storm morphology of the adjacent beach. Understanding the patterns, if any, defining these types of extreme storm events is crucial for predicting the frequency of future storms as well as planning for the mitigation of potential storm impacts.
Smith, Stephen G., "A SEDIMENTARY RECORD OF INTENSE STORMS AND ENVIRONMENTAL CHANGE FROM A COASTAL FRESHWATER LAKE IN REHOBOTH BEACH, DELAWARE" (2010). Open Access Master's Theses. Paper 2030.