MARINE DEPOSITIONAL HISTORY: AN ANALYSIS OF BLOCK ISLAND, RI HURRICANES

Strong storms ravage the Caribbean islands and the southern and eastern coasts of the United States and seem to increase in their intensity and frequency by the year. The resultant destruction can cause entire societies to re-build their infrastructures and ways of life. Hurricanes tend to raise sea level, erode sand beaches, and cause marine sediments to overwash onto land and into back-barrier marshes and ponds. Block Island is a prime location for these washover fan storm deposits. This pilot project explores the history of hurricane and northeaster strikes on the northern end of Block Island. Sediment cores collected from Middle Pond on Block Island were analyzed for storm washover fans by using bulk grain size, radiocarbon dating, magnetic susceptibility, and foraminiferal and thecamoebian abundances. Foraminifera that commonly reside in salt-water are offshore-indicative taxa while thecamoebians are most commonly found in both freshwater and slightly brackish environments. Within the core “MP-2,” collected from the center of Middle Pond, 24, 1 cc samples revealed a total of 1,040 thecamoebians and 112 foraminifera. The microfossils were largely concentrated toward the top of the core. Regarding large-scale grain size measurements, gravelly sediments inundated only the lower 40 cm of the approximately 120 cm core, and the upper 80 cm were composed of alternating sand and mud dominated layers. Sand layers within the cores have been assumed to represent direct strikes by major hurricanes of category four or five intensity, such as the 1635, 1815, and 1938 hurricanes and more recent storms. Collected data shows records that the core dates to ~3,420 BP +/-34 yr, when the geologic environment of Block Island was very different than it is today.