DOCUMENTING LANDSLIDES IN THE DRIFTLESS AREA OF SOUTHEASTERN MINNESOTA

Landslides pose a threat to infrastructure, to the environment, and most importantly, to human lives. The goals of our research are to identify and document both recent and historical landslides that have occurred in Southeast Minnesota (Wabasha and Goodhue counties). Ultimately, this inventory will be incorporated into a state-wide effort to inventory landslides and develop a predictive model of landslide hazards throughout Minnesota.

Southeastern Minnesota is especially prone to landslides because of its geologic history. It is part of the Driftless Area, a region that was largely ice-free during the Pleistocene Epoch, and because it is an older landscape than the surrounding glaciated terrain, the Drifless Area is characterized largely by deeply incised river valleys. Further, the trunk Mississippi River valley and some tributaries were carved, in part, by glacial meltwater. Another characteristic of this area is steep bluffs where thick sequences of Paleozoic carbonates cap more easily eroded sandstones and shales, creating vertical cliff faces throughout much of the region. These steep river valleys and loosely consolidated sediments and soils create prime conditions for landslides.

The steep bluff faces in the region contribute to many rock falls, while slides and debris flows appear common where there is significant soil development on slopes, primarily over sandstone and shale bedrock. Mudslides often occur during heavy precipitation events, quickly delivering water and sediment to the bottom of incised valleys. Earth slump landslides are also common in Southeast Minnesota as a result of near-surface bedrock overlain by a layer of loess. Modern landslides have been found most frequently in areas where slopes have been oversteapened by roadcuts and in valleys where rivers are eroding into valley walls.