CHARACTERIZATION OF LARGE LANDSLIDES RELATED TO THE PRESUMPSCOT FORMATION, SOUTHERN MAINE

Maine’s glacial marine clay unit, the Presumpscot Formation, is present throughout southern Maine and presents challenges to development, infrastructure, and public safety in the most populated area of the state. Landslides associated with the Presumpscot Formation have occurred in river corridor and coastal bluff areas of southern and coastal Maine throughout historical and modern times. The largest recorded historical landslide (about 15 ha) happened along the Presumpscot River in 1868, but most of these known landslides have been relatively small (<10 ha). LiDAR topographic data recently revealed over 100 large landslides in southern Maine, ranging from tens to hundreds of hectares. The Maine Geological Survey has been working with assistance from the Maine Emergency Management Agency to determine the characteristics of these large landslides. A subset of landslides was chosen for more detailed investigation, in which vegetation that was buried by, caught up in, or deposited on the landslides was sought for radiocarbon dating of the features. Prior to this study, only one pre-historic landslide had been dated to about 13,500 cal yrs BP. Improved understanding of the timing and potential triggers of these previously unknown landslides that were revealed by LiDAR will help guide disaster preparedness.