Modelling River-Dune Interactions on Ancient Mars

Abstract

Aeolian and fluvial processes on Earth show significant interactions. Within terrestrial desert environments, analysis of ~200 locations has revealed that where ephemeral or episodic rivers flow across a dune field the predominant processes alternate between aeolian and fluvial, and that when rivers and dunes are active, they interact with one another. Avulsions can be major, with channels in the northern Kalahari having cumulative diversions of 10s of km. Considering Mars likely had an arid environment during the period of peak fluvial activity, the presence of fossilised Martian dunes, and observations by the Curiosity rover of fluvially altered aeolian deposits, it is apparent that Mars likely experienced simultaneous fluvial and aeolian processes, and periods of fluvial inactivity where aeolian processes persisted. At present, Martian aeolian and fluvial processes have only been studied independently, and their interaction has not been explored.Here we report the initial study by the Working group on Aeolian-Fluvial Terrain Interactions (WAFTI), based at the European Space Agency, which examines the effects of these processes in synergy under ancient Martian conditions, using a combination of modelling and geomorphological analysis. We hypothesise that these interactions could have implications for a number of Martian phenomena, for example: the prevalence of meandering inverted channel systems, the distribution of organic material, the discordance of Martian valley networks, and the sediment size and distribution of Martian rivers. In this study, we simulate the interactions between migrating dunes and different reaches of an active river channel, under ancient Martian conditions to determine the effects on the channel’s morphology and geometry.Our Martian Aeolian-Fluvial Interactions (MAFI) model is a landscape evolution model based on a coupled implementation of the Caesar-Lisflood fluvial model, and Discrete ECogeomorphic Aeolian Landscape model (DECAL) dunes model. It routes water over a Digital Elevation Model (DEM) and calculates erosion and deposition from fluvial and slope processes changing elevations accordingly. Aeolian material is discretized into slabs on the DEM, and slabs are moved across the space according to a set of simple rules.At EGU we will present the results of our simulations of aeolian and fluvial interactions on an inclined plane with a central channel and a continuously flowing Martian river. Typically on Mars, channels are housed within valleys with V or U-shaped cross-sections. Additionally, the topography of Mars is heavily altered by impact craters, many of which are sediment sinks. Finally, the profiles and immaturity of Martian valleys indicate that they were likely ephemeral/episodic, so flow was unlikely to be continuous. We, therefore, plan to expand our study to simulate the following: (1) simulate continuous flow for a DEM with a V-shaped valley and central channel; (2) “” U-shaped valley and central channel; (3) “” for a DEM with a crater present adjacent to the part of the valley; (4) simulate episodic fluid flow with periods of no fluvial activity, but continued aeolian activity. Understanding these two major surface processes in synergy will aid in the reconstruction of Mars’ ancient paleoenvironments in a way that has not previously been explored.