LANDSLIDES IN NORTHEAST MINNESOTA: INVENTORY MAPPING AND SUSCEPTIBILITY ASSESSMENT

Landslides and other mass-wasting processes such as streambank failure are common geomorphic events in the steep post-glacial landscapes of Minnesota. They can impair water quality, damage infrastructure, and pose risks to human life. This research focuses on the assessment of slope instability across northeast Minnesota as part of a larger collaborative state-wide landslide inventory and susceptibility mapping project. We used Google Earth imagery and repeat aerial lidar data to identify and map historical slope failures at a scale of 1:3,000, excluding features less than 2 meters tall. Much of the mapping of historical events focused on a record storm event in June 2012 during which 20-25 centimeters of rainfall occurred over 48 hours, causing extensive flooding and triggering numerous mass-wasting events. Field reconnaissance confirmed remotely mapped locations of landslides and identified active unstable slopes. We used open-source statistical software to conduct logistic regression analyses of slope instability factors including slope angle, roughness, distance to stream, depth to bedrock, and material composition.

Slope failures are concentrated in thicker glacial sediments along river valleys and the Lake Superior shoreline. These are driven by hydrologic factors such as channel incision, toe-cutting, lateral migration, sapping, and wave action. Slope failures are more frequent in areas containing glacial-lake deposits that were destabilized in response to the 2012 flood. Head scarps initially triggered by the flood in these areas continue to propagate upslope seven years later. Uphill facing scarp features and undulating hummocky topography provide evidence of past movement that may contribute to poor drainage and saturation of modern slopes.

This landslide inventory and susceptibility analysis will allow stakeholders and decision-makers to reduce the risks from future landslides.