A Major Missing Component to Martian Surface Evolution and Habitable Environments - Aeolian-Fluvial Interactions

Mars’ surface is carved by thousands of valley networks (VNs), which are evidence of ancient flowing rivers, which were most active ~3.7 Byr ago, a period coined “the warm and wet period”. Although it was wetter than present, recent analysis of paleolake deposits and the branching angles of VNs indicate that Mars was arid during this period, similar to terrestrial deserts. Additionally, geomorphological evidence indicates that these rivers were episodically active, with reactivation periods of years. In deserts on Earth, fluvial (flowing water) and aeolian (wind-blown) (AF) processes display considerable interactions, which have an impact on dune and river trajectories, morphologies, geometries, and distributions. These interactions can lead to water loss to the subsurface and the formation of sabkhas, which are interdune ponds that transform into salt flats. These pools are where primordial continental life on Earth emerged, evidenced by microbial mats. Geological evidence on Mars, such as lithified dunes and interwoven inverted river channels, and the discovery of aqueously altered lithified dunes by the Curiosity rover, indicates synergy between AF interactions on ancient Mars. However, the combined influence of AF processes on Martian landscapes has not yet been fully explored.

Here we report the results of the pilot 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. 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. We conduct simulations of various scenarios to model the interactions between perennial and ephemeral rivers, actively migrating dunes, and different types of terrain (bedrock and unconsolidated sediment). These simulations incorporate factors such as evaporation and water loss to the subsurface.

These interactions have a number of salient impacts: meandering inverted channels, the sediment size and distribution of Martian rivers, the formation of interdune pools, and the preservation of Martian VNs.