Prudence Island - Narragansett Bay, RI

Geology

Approximately half of North Prudence is glacial till and the other half is glacial outwash. Near Pine Hill (the outwash area) is a kettle hole created during the glacial period. This depression interrupts groundwater, so the kettle hole has become a small pond. The glacial till near Potter Cove and in the vicinity of the old airstrip is classified as Newport silt loam. The silt in this rich soil retains moisture better than the sandy outwash soils that cover much of North Prudence. Several features exemplify the dynamic aspect of coastal geologic processes. A bay spit in front of Jenny Creek is moving into the salt marsh at a rate of about one meter per year. A recurved spit, Gull Point is continually growing and being reshaped by the northeast and northwest winds.

There are extensive salt marshes on the west side of the island. These marshes, like most salt marshes in the northeastern United States, are believed to have been formed in the past 3,000 to 4,000 years, a time when relative sea level has been slowly rising at approximately one mm per year. These marshes have been ditched since, probably during the 1930s in order to control mosquitoes. By 1938, almost 90 percent of the salt marshes from Maine to Virginia had been ditched in this way.

Central and South Prudence have fields and forested uplands. The soil is glacial fill overlying a shale bedrock.

Prudence Island

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