Abstract
Despite relatively low relief topography, slope failure events are the major contributor of excess sediment to many Minnesota watersheds, negatively affecting water quality, riparian ecosystems, fisheries, and recreational facilities. In addition to posing an acute natural resource management challenge, hazardous, eroding slopes in the Minneapolis-St. Paul area have caused damage to infrastructure and loss of life. Since 2013, there has been one fatal landslide, a landslide that posed a hazard to a major medical facility, and a rockfall landing on a major street. The current lack of a landslide hazards map or mitigation strategy for the dynamic and evolving landscape of the Upper Mississippi River valley leaves cities vulnerable to further damages and rivers subject to episodic sediment loading. Furthermore, the public is largely uninformed of these issues. Lidar-based landslide inventory mapping protocols were established by Oregon and Washington State in 2009 and 2017, respectively, to quantify past landslide frequency and to mitigate future losses from landslides. To better understand how and where landslides occur in the metropolitan center of Minnesota, a landslide inventory modeled after those of Oregon and Washington State was initiated in 2017. A preliminary phase of historical research found 64 documented slope failure events dating back to 1852. One-meter resolution lidar map derivatives were then used to identify undocumented landslides over an 8300 km (super 2) area based on the presence of diagnostic geomorphic features including headscarps, internal scarps, convex surfaces, hummocky topography, displaced streams, and lobate toes. Areas in which these features were identified were field-checked to confirm their presence and to evaluate the interpretation that they were historical landslides. Field work was also conducted to evaluate evidence and location of landslides identified from the historical records search. This work is part of a larger effort to create a landslide inventory across much of Minnesota where slope instability occurs. It will result in development of a digital database of slide locations and characteristics across the study areas, which will be used in the future production of a landslide susceptibility map.