Revisiting Rock Mass Indices: Improving and Applying the Measurement of Erodibility

Erodibility is an important factor in studies of geomorphology. Along with other factors such as climate, time, and tectonics, it contributes to the shape and evolution of landscapes. Several methods exist to quantify erodibility that examine rock mass properties such as fracture characteristics and strength of intact rock. These systems can be used to predict such varied properties as the slope of a rock mass, the geometry of bedrock channels, and the likelihood and type of potential slope failures. Yet, these systems are limited by shortcomings such as subjectivity, limited calibration, and failing to produce reasonable predictions of slope when rocks are mechanically or chemically weak. To address these and additional issues, original and modified versions of three erodibility rating indices are applied in a variety of lithologic, climatic, and erosional environments. Ratings are compared to topography for calibration purposes and to examine whether erodibility and topography will correlate in all environments studied. Several of the techniques tested are successful at improving ratings' correlation to topography in slowly eroding landscapes, while other landscapes do not correlate to ratings. A new adjustment factor for chemically weak rocks further improves this correlation in certain environments. Finally, suggestions are made for the future use of erodibility indices that incorporate specific techniques and alterations from the study as well as general impressions from use.