LANDSLIDES IN THE RED RIVER VALLEY, MINNESOTA

Despite its low relief, the Red River Valley in Minnesota does experience mass wasting, including landslides. Thousands of slides, primarily along rivers or lake shores, have been identified using airborne lidar data, and a subset of these have been field-verified. The size and failure mechanism of these slides changes throughout the valley in response to west-to-east changes in the surficial geology. Along the western edge of Minnesota, near the axis of the valley, the sediment is dominated by offshore glacial Lake Agassiz deposits of clay and silt which fail slowly as shallow slides, often as a result of changes to the vegetation or overburden. Moving a few tens of kilometers east into the near-shore Lake Agassiz environment, deposits are dominated by interbedded lacustrine and fluvial sands. Rivers in this area are deeply incised and form steep bluffs that can lead to large rotational failures. Farthest to the east towards the edge of the Red River valley watershed, rivers are less incised with lower river banks, but small rotational failures still occur in glacially dominated sediments. This inventory of Red River Valley landslides is a component of a greater Minnesota landslide mapping effort and highlights the need for understanding the variety of factors that contribute to landslide hazards in the state.