Geomorphometric mapping of Zagros Ranges at regional scale

Abstract

A method for regional-scale geomorphometric mapping that is useful for morphotectonic studies is presented for the Zagros Ranges in Iran. The DEM-to-Mount transformation, a region-growing algorithm for terrain segmentation is implemented. To cope with the specific conditions in that compressional-morphotectonic context, the transformation was modified: region growing was not allowed for valley pixels; ridge pixels were used as seeds; and the growing criterion was based on gradient. The landscape was decomposed to two terrain classes (mount and non-mount) and to isolated mountain objects that were numerically represented on the basis of appropriate attributes (mean and maximum elevation, gradient, hypsometric integral, size). The domain of the attributes was sliced to intervals on the basis of geomorphometric criteria and their spatial occurrence. Finally, the landscape was characterized on the basis of mountain morphometry from the spatial distribution of the classes. The objects greatest in size were observed in the NW. Three distinct regions with respect to the mean elevation were spatially distributed in increasing mean elevation from SE to NW, producing stair-step topography at a regional scale. In the NW, the degree of dissection was less and objects with the highest gradient were observed. These observations suggest that at a regional scale the main NW topographic units have not been significantly downcut towards sea level, for a pattern of small isolated objects with lower mean elevation, gradient and hypsometric integral to be formed as those observed in the SE.