Automated mapping of conformity between topographic and geological surfaces

Abstract

We present a technique to produce spatially distributed fields of geometric alignment between topography and the orientation of geologic bedding planes (topographic/bedding-plane intersection angle). Computation and digital mapping of the topographic/bedding-plane intersection angle (TOBIA) requires the derivation of four spatially distributed variables: topographic slope, slope aspect, bedding dip, and dip azimuth. Slope and slope aspect surfaces are derived from a high resolution (10 m) digital elevation model. Ordinary kriging is used to interpolate spatially continuous fields of dip azimuth and dip from point measurements of strike and dip. Using these variables, TOBIA can be mapped either categorically as slope types, or as a continuous index. Categorical mapping requires two steps. First, slopes are classified into three functional types based on the alignment between the dip azimuth and slope aspect. Slopes are then further partitioned based on the alignment between slope angle and dip angle. Continuous computations of TOBIA rely on a geometric equation using all four variables. The methods provide an efficient means for estimating topographic/bedding plane intersection angles over large areas. Resulting surfaces are useful for a variety of landscape-scale modeling applications, such as the prediction of potential hillslope failure, hydrologic flow paths, and vegetation patterns.