Effect of far‐field slope on morphologic dating of scarplike landforms

Abstract

The principal finding of this paper is that the far‐field slope has a first‐order effect on model age determinations of scarplike landforms in weakly consolidated terrains. Observationally, this can be demonstrated in two ways using the Lake Bonneville and Lahontan shoreline scarps as separate and combined data sets. Use of the reduced scarp slope, tan θs ‐ b (where θs is the maximum scarp angle and b is the far‐field or fan slope), instead of tan θs alone as the measure of scarp slope measurably reduces separation between the two data sets induced by different average fan slopes for the two data sets and significantly reduces scatter in the slope‐offset plot for both the separate and combined data sets. Theoretically, the argument can be put even more strongly, at least within the range of linear and nonlinear diffusion models that we consider here together with a mathematical transformation of the empirical approach of R. C. Bucknam and R. E. Anderson: When one correctly takes into account the far‐field slope, one will basically get the same age determination no matter which of these models one uses; conversely, without accounting properly for the effect of far‐field slope, one is virtually guaranteed to get an erroneous age determination, no matter which model is used.