CHARACTERIZATION OF LANDSLIDES IN SENSITIVE CLAY, SOUTHERN MAINE, USA

Landslides have been a documented hazard in Maine since early written historical accounts in the late 1600s, but lidar topographic data recently revealed hundreds of previously unknown prehistoric features. While landslides can occur statewide, prehistoric through modern events are far more common in southern Maine due to the presence of a sensitive glaciomarine clay deposit known as the Presumpscot Formation. Much of Maine’s recent population growth and development is occurring in southern areas of the state with extensive landslide histories, so this is of particular concern for the future of this region. The Maine Geological Survey has been working to inventory and characterize all landslides in Maine, and to determine the ages of many prehistoric events related to the Presumpscot Formation in order to better understand factors that may have caused these failures. Landslide morphologies range from small (< 1 ha) rotational slumps in river corridor and coastal bluff areas to large (up to 250 ha) spreads and flows. Historic and modern landslides have been associated with wet conditions and/or river bank and coastal bluff erosion, and prehistoric landslides were initially assumed to be related to an unstable early post-glacial landscape. Radiocarbon dating of vegetation that was buried by, caught up in, or deposited on prehistoric landslides found that events have been occurring in Maine throughout the Holocene. Clusters of landslides in space and time may be related to large earthquakes or especially wet periods. A cluster of landslide activity around 600 cal yrs BP is particularly noteworthy as it may be related to a regional climate transition documented in other paleoenvironmental records.