High-resolution DTM-based estimation of geomorphometric parameters of selected putative martian scoria cones

Abstract

Some previous studies have identified a number of features on Mars that are thought to be scoria cones. Since (terrestrial) scoria cones have special significance that they are monogenetic volcanoes, i.e. the volcanic edifice is created by a single eruptive event. The process usually produces fairly symmetrical cones, making them a target for morphometric research. In this study, we investigated features that were interpreted as scoria cones (or mud volcanoes), which are included in the HiRiSE database of stereopairs and thus, high-resolution DTMs can be generated for their area. We have computed DTMs using the tools of NASA Ames Stereo Pipeline and USGS ISIS system and calculated classic (cone width, cone height, crater width) and other volcano-geomorphometric indices and derivatives based on the elevation data. Polar Coordinate Transformation (PCT) images have been calculated in order to analyze the symmetry of the cones. Spatial Elliptical Fourier Descriptors (SEFD) have been computed to model the outer contours and the crater rims. The parameters (especially those of the fitted ellipses) are analyzed in order to visualize the orientation and extent of the properties of the cones. The classic relationship of the cone widths and cone heights can also be established for the Martian scoria cones. However, while for the terrestrial cases, a factor of 0.20–0.22 has been determined in the last decades, for the analyzed putative Martian scoria cones this factor is below 0.2, according to our calculations, they are in the range of 0.16–0.19. The analysis of the elevations of the cone contours reveals that in most of the cases the pre-eruptional surface could have been subhorizontal and flat. The fitted ellipses of SEFD method have a remarkably constant ratio of the lengths of the semimajor and semiminor axes, both for the outlines and for the crater rims. Although the contours and rims are slightly elliptical in most cases, our results show a high degree of symmetry in the selected cones. This symmetry is considered to be due to two main reasons: first, it is the result of a selection effect, as only those cone-shaped features are included in the study that are very probably scoria cones, and second, due to the different Martian conditions from those on Earth, in certain cases there is degradation on these cones, with e.g. at most minor mass movement traces modifying the high degree of symmetry.