COASTAL LANDSLIDE AND BLUFF HAZARD IDENTIFICATION AND MAPPING ALONG THE "ROCKY" MAINE COAST

Late Quaternary glaciation and Holocene transgression have produced an immature and erodable sedimentary shoreline along much the Maine coast. Driven by a 2 mm/yr sea-level rise, chronic land loss continues to reshape the shore, particularly along inner bays and estuaries where sediment bluffs are common. Over 2000 miles have been mapped from the shore of the Piscataqua River at the Maine-New Hampshire border to Castine in Penobscot Bay for bluff and landslide hazards. Bluff erosion affects about 10 times more shoreline length than beach erosion in Maine.

MGS Coastal Bluff maps show bluff stability and shoreline type along the base of the bluff, describe the origin of bluffs, the chronic nature of bluff erosion, and illustrate the shoreline complexity. For the mapped region, 53% (1080 miles) of the coast has sediment bluffs. Of this distance, 760 miles of bluff shorelines are in the low-risk, stable category. Unstable bluffs occur along 280 miles and highly unstable bluffs along 40 miles. The majority of these 320 miles of unstable bluffs include highly valuable waterfront real estate. As high clay bluffs erode, they also become susceptible to landslides; lives and property have been threatened recently by slope failures.

A new map series, Coastal Landslide Hazards, compliments the Coastal Bluff maps and identifies historical landslide sites and potential landslide areas. Risk was identified based on the existence of a sedimentary bluff and the geology and geomorphology of past failure sites. Field observation, air photographs, and map analysis, were used to map shorelines with a potential for landslides. Understanding bluff erosion and coastal landslides will help homeowners site new structures in safe locations and inform others about existing risk to property. Future development located away from hazard areas will reduce the need for expensive coastal engineering and simultaneously preserve natural environments along the Maine coast.