HISTORICAL LANDSLIDES WITHIN THE METROPOLITAN MINNEAPOLIS-ST. PAUL AREA

Minnesota’s wettest recorded month in June 2014 led to widespread gravitational failure of sediment and rock in the metropolitan area of Minneapolis-St. Paul. The failure beneath the oxygen supply for Fairview Riverside hospital was costly enough to allow the entire state to qualify for a federal disaster declaration. Two years prior, a similarly rainy period resulted in loss of life as well as extensive property damage. Our goal is to develop a better predictive model of when and where failures occur in order to inform hazard response plans, best management practices and to develop model ordinance language.

We inventoried historical failures in a broad region that included the metropolitan area by searching online sources and print newspaper archives. We interviewed Minnesota Department of Transportation personnel with extensive knowledge of problematic areas in heavily engineered landscapes near roadways. Failures were mapped onto a 1m-hillshade DEM created with LiDAR data at a density ranging from 1.5 to 8 data points per square meter. Failure scars discovered on the DEM and not through the historical archives were noted and municipalities contacted for more information on timing. The antecedent precipitation for two to four weeks prior to the failure and soil moisture conditions at the time failure were extracted from climate archives for the periods identified.

Nearly all of the slides occurred between May and October with peaks in June and August, both periods of higher incidence of convective storms in Minnesota. The earliest record of failure was in 1879. Wet periods in the late 1890s, early 1900s, 1980s and 1990s are reflected in an increase in reporting of slides. The increase in slides reported since 2010 may reflect the wetter climate as well as the ease of searching online records. The failures were primarily located along the Mississippi and Minnesota River corridors.