Morphological and hydrological analysis of volcanic flank valleys – Evidence for a volcanic origin

Abstract

Valley networks incising the flanks of Martian volcanoes are potential evidence of geologically recent fluvial activity, either via geothermal heating of snowmelt and groundwater upwelling [Gulick and Baker, 1989, 1990; Gulick et al., 1997; Gulick, 2001; Hynek et al., 2010], or summit snowpack melt [Fassett and Head, 2006, 2007]; however, their origin remains uncertain [Carr, 2012]. In this study, detailed morphological, geometric and palaeohydraulic [Hack, 1957] analysis was performed on seven valley networks. Four are Martian valley networks incising the flanks of Alba Mons, Hecates Tholus and Ceraunius Tholus. Considering they may have a magmatic origin, the results of the analysis were compared to several Martian valleys incising volcanic plains and a lunar sinuous rille system, adjacent to Rimae Prinz, to determine whether they bear similarities and may have formed via a similar process. The morphologies of the three small valleys incising the flanks of Alba Mons, Hecates Tholus and Ceraunius Tholus are similar to those incising volcanic plains and the lunar sinuous rille (e.g., width:depth ratios of ∼3). In high-resolution imagery (Context Camera – 5 ​m per pixel; HiRISE - ∼0.5 ​m per pixel), pits can be observed throughout these valleys, which are potential evidence for collapsed lava tubes . The paleohydraulic analysis of these networks indicates that they did not likely form via precipitation-fed fluvial activity and, in some areas, the surface would cause drainage away from the valley trough. However, some of the volcanic flank valleys have small sedimentary deposits at their termination. A combination of these results indicate that they likely formed primarily as a result of tube-forming eruptions and subsequent lava tube collapse, followed by later periods of channel-forming eruptions. If subsequent fluvial activity did take place, resulting in the small sedimentary fans seen at the base of the some of the networks, it was likely the result of short-lived ice/snow melt, which flowed through the pre-defined lava channels. • Morphological and hydrological analysis of seven Martian valleys on volcanoes and volcanic plains, and one lunar rille. • The majority of the valleys bare resemblance with the lunar rille. • The valleys do not follow the scaling relationships expected for fluvial valley systems. • Most valleys likely formed from volcanic activity. • Some of these valleys were likely modified in post by fluvial activity.