Relative instability of colluvium‐filled bedrock depressions

Relative instability of colluvium‐filled bedrock depressions Regolith landslides commonly occur in colluvium‐filled bedrock depressions rather than on ridges, spurs, or sites with planar bedrock surfaces. Drained direct shear tests of colluvium from bedrock depressions in Wellington, New Zealand, indicate the presence of cohesion in all samples, suggesting that thickness of accumulated deposits may become a limiting factor for stability. Critical depths for a range of slope angles were calculated (assuming conditions of infinite limiting equilibrium) and compared to the depth/angle relationships for depression and interdepression regolith occurring in the field. The results indicate that, under saturated conditions, interdepression regolith is not thick enough to permit the development of landslides. Colluvium‐filled bedrock depressions, on the other hand, generally exceed critical depth and must be considered susceptible to landsliding in the absence of any significant root cohesion. The age of deposits and the abundance of unfailed colluvium‐filled bedrock depressions suggest that they have been inactive for most of post glacial time. Stability analysis, verified by observing the occurrence of landslides, indicates that recent instability has been brought about by deforestation. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Earth Surface Processes and Landforms Wiley

Relative instability of colluvium‐filled bedrock depressions

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Abstract

Regolith landslides commonly occur in colluvium‐filled bedrock depressions rather than on ridges, spurs, or sites with planar bedrock surfaces. Drained direct shear tests of colluvium from bedrock depressions in Wellington, New Zealand, indicate the presence of cohesion in all samples, suggesting that thickness of accumulated deposits may become a limiting factor for stability. Critical depths for a range of slope angles were calculated (assuming conditions of infinite limiting equilibrium) and compared to the depth/angle relationships for depression and interdepression regolith occurring in the field. The results indicate that, under saturated conditions, interdepression regolith is not thick enough to permit the development of landslides. Colluvium‐filled bedrock depressions, on the other hand, generally exceed critical depth and must be considered susceptible to landsliding in the absence of any significant root cohesion. The age of deposits and the abundance of unfailed colluvium‐filled bedrock depressions suggest that they have been inactive for most of post glacial time. Stability analysis, verified by observing the occurrence of landslides, indicates that recent instability has been brought about by deforestation.

Journal

Earth Surface Processes and LandformsWiley

Published: Jun 1, 1990

References

  • Landslips in Wellington City
    Eyles, Eyles; Crozier, Crozier; Wheeler, Wheeler

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