LANDSLIDE SUSCEPTIBILITY MAPPING IN MAINE

Landslides threaten lives and property throughout the United States causing in excess of $2 billion in damages and 25 to 50 deaths annually. In Maine, no systematic analysis of the landslide threat statewide has been undertaken. During the spring of 2005, 2006, and 2007, heavy precipitation/flooding events in Maine caused many damaging landslides, with damage estimates in the millions of dollars. This uptick in landslide occurrence, magnitude, and damage, led to a pilot project between the Maine Geological Survey (MGS) and the Maine Emergency Management Agency (MEMA) to 1.) update Maine's inventory landslide database; 2.) develop methodology to examine and map landslide susceptibility and their causative factors; 3.) collect data on direct losses caused by landslides. This in turn has led to further funding to inventory and map landslide in areas of Maine underlain by the marine clay of the Presumpscot formation.

In the pilot project, 4 Maine towns (Cumberland, Wells, Bangor, and Greenbush) were selected for study. The towns are located on the glaciomarine clay of the Presumpscot formation and have suffered recent damaging landslides involving the marine clay.

Direct field mapping and aerial-photography interpretation was utilized to update Maine's landslide inventory database. Data layers of potential landslide risk factors were created from available geologic datasets and slope factors derived from digital elevation model (DEM) data.

Mapped landslide localities are strongly correlated with slope, slope aspect, relief, curvature, and surficial geology. For landslides localities mapped for the pilot study, 91% are located in areas with a slope greater than 5 %, and 83% are located in areas with at least one additional risk factor. These strong correlations demonstrate that the landslide susceptibility maps produced are good predictors of where landslides are likely to occur.

These developed landslide susceptibility maps can be used in developing hazard mitigation and land development policies for State and local authorities here in Maine.