Beginning in the early 1990‘s, a portion of Deer Creek, a tributary of the Nemadji River in the Lake Superior basin, experienced the formation of sediment volcanoes in its creek bed, along with related slumping, enhanced erosion rates, and turbidity in excess of state total maximum daily load (TMDL) limits. Slumping near the stream has increased erosion rates and may eventually threaten the stability of nearby structures. The resulting excess turbidity negatively impacts aquatic wildlife, and increases sedimentation rates and dredging costs in downstream navigable waters.
Slumping and formation of sediment volcanoes at Deer Creek were likely caused when dynamite was used to destroy a nearby beaver dam on the creek. Some combination of rapid pond drainage and/or disturbance from the explosives may have led to fracturing of a glacio-lacustrine clay confining layer over a locally extensive aquifer. A sediment volcano and associated slumping are also present along nearby Mud Creek. The sediment volcano areas at Deer and Mud Creeks both occur at the toe of 10-meter high slumps. The failure planes of these slumps may facilitate formation of sediment volcanoes by providing pathways for groundwater to reach the surface. Predicting slump locations should then also help predict the location of potential sediment volcanoes.
The stratigraphic and hydrologic conditions in Deer and Mud Creeks are similar to those throughout nearby areas in the Nemadji River basin. This project examines the relationship between the slumps and sediment volcanoes, and develops a predictive model of the potential for slope failure in the lacustrine clay portions of the basin. A 3-D model of stratigraphy and hydraulic potential from more than 300 wells is used, along with slope stability analysis with the stress-slope and Mohr-Coulomb equations in a GIS.
Results of the modeling found higher susceptibility for slumping in areas of high slope and high potentiometric surface. The model correlated well at a 92% rate with a data set of 322 inventoried slumps, and included both volcano areas, without overpredicting high-risk slump areas. Another model, SINMAP 2.0, was run to test the veracity of the original model‘s results. Both models were in good agreement with each other. This project provides a reasonable approximation of slope stability and can be used to assist in land use planning to help reduce erosion and its consequences.
University of Minnesota M.S. thesis. June 2010. Major: Geological Sciences. Advisor: Dr. Howard Mooers. 1 computer file (PDF); vi, 80 pages. Ill. (maps col.)
Mossberger, Irvin Gerald.
Potential for slumps, sediment volcanoes, and excess turbidity in the Nemadji River Basin..
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