Kansas Geological Survey, Current Research in Earth Sciences, Bulletin 244,
part 3
The Relationship Between Geology and Landslide Hazards of Atchison, Kansas, and Vicinity--page 8 of 9
Conclusions
The key factors contributing to landslide problems in the study area include slope angle, hydrology, geology, soils, and slope line. Rock-fall and rock-topple hazards are associated with areas of exposed limestone, especially areas where exposed limestones overlie shales that are being eroded. Recent landslides, which are dominantly earth slides and earth flows, generally occurred in bedrock and soil developed on bedrock, but almost every rock unit mapped in the area had at least one recent landslide. Shale formations were more susceptible than limestone formations to slope failures; however, weak shale members of limestone formations can also cause problems. Recent landslides occurred on moderate to steep slopes, but some are found on gentle slopes (5 degrees to 15 degrees). Recent landslides were most likely to occur on slopes with either southeast to northeast or northwest orientations. The Lawrence Formation was the most landslide prone unit.
Thin (less than 0.3 m or 1.0 ft) clay layers within the shale formations and the shale members of limestone formations play an important role in causing landslides. These layers have a high percentage of clay-sized particles, which include expansive clays. Thus, these layers are planes of weakness and can become the failure planes of landslides. Additionally, these clay layers, along with the clays in the siltstones and residuum from weathering the limestone, are sources of clay minerals to the soil.
Landslide hazards should be considered in the planning and design phases of construction in the Atchison area. This is particularly important in such areas as the bluffs along the Missouri River and its tributaries that have exposed or subsoil shale units. Many options exist for mitigation and remediation of landslide hazards. The best is to avoid areas that are susceptible to landslides. It is recommended that a qualified geotechnical or civil engineer with the assistance of a geologist examine the slopes and make recommendations. It is also important that the recommendations of the engineer be followed.
Acknowledgments
The author would like to thank Charles Baskerville, Helen Delano, John Gosse, John Moylan, and Charles Cammack for their helpful and insightful reviews. Additional thanks go to Mike Magnuson for the X-ray diffraction work at the Kansas Geological Survey.
Kansas Geological Survey
Web version December 22, 2000
http://www.kgs.ku.edu/Current/2000/ohlmacher/ohlmacher8.html
email:lbrosius@kgs.ku.edu