Delivered at 2008 Boston Harbor Islands Science Symposium.
Boston Harbor Islands is a drowned drumlin field—a unique geological formation within the North America. Since sea level has risen enough to flood the glacial features left by the last Ice Age, geomorphic and coastal processes have reshaped the islands. Boston Harbor features a large range of coastal environments from rocky shores and eroding bluffs to sandy dunes and several small salt marshes. Eroding till, drumlins have provided the sediment source for the accretionary landforms. Researchers have been investigating the mechanisms of bluff retreat and the factors governing the sediment transport pathways and rates.
Geologists have mapped the islands in terms of bluff condition and the shoreline, and are monitoring the eroding bluffs. While 80 percent of the drumlin bluffs are stable, others have been retreating at varying rates (over 2 meters per year on Lovells Island). Lower retreating rates have been observed within the inner harbor, while faster rates occur nearer the open ocean. Data shows clear relationships between bluff height and the process of retreat. Dr. Hughes focuses on the wave climate as the dominant hydrodynamic influence in the Harbor and have modeled the wind driven waves using the Simulating WAves Nearshore (SWAN) model. In addition to studying natural waves, she has assessed anthropogenic influences, specifically boat wakes, in order to gauge their impact on the evolution of the Island coastlines. The data demonstrates that boat wakes transport sand and fine sediment, but do not impact bluff retreat.
Ultimately, sea-level rise is driving the development of the islands' landscape. Future studies will investigate how the system is responding to rising sea level, specifically the impact to till bluffs, “salients” and salt marshes.
