The Boston Harbor Islands (a National Park Area) are part of the only coastal drumlin field found within the United States. Historical aerial photographs of selected islands were used to identify long-term sedimentation trends that can explain the modification of the islands’ geomorphology. All photographs were converted to digital format and georeferenced to the same coordinate system within a Geographic Information System. This helped to facilitate data analysis and illustrate the extent of shoreline evolution on each island.

The natural processes responsible for reworking sediment around the islands are storms, wind-generated waves inside the harbor, tidal currents, and slope failure, all operating in a regime of accelerated sea-level rise. Some sections of the Harbor Island shorelines suggest that actively eroding bluffs and beaches can be found at locations with very small wave fetch, yet adjacent to fast commuter boat routes (Grape Island, Webb State Park). Erosional scarps and accretionary features such as beach dunes and tombolos found along the island shorelines are attributed to both natural and man-induced processes. Each island experiences erosion due to one of three main factors. Areas of shoreline exposed to the ocean and northeast storm waves, beaches that erode by local wind-generated waves, and erosion due to boat wakes. Erosional trends were also related to the composition and geotechnical properties of slope sediment, overland flow, and the abundance or lack of vegetation in an exposed area. The driving processes behind sediment transport cells, which modify island morphology, may not have natural origins such as ambient waves and tides. This potential anthropogenic influence, superimposed upon island evolution during a continual rise in sea-level, has high potential to impact the future stability of island shorelines.

Historical aerial photograph analysis along with fieldwork data documenting seasonal change will serve as a foundation study of long-term shoreline evolution and may be useful for future research on natural and human processes responsible for shoreline erosion. This information will also be of value for future planning of park facilities as well as contributing to the preservation of important natural and cultural resources.