The impact of brines on channel morphology

On Mars, there is evidence of a multitude of ancient single-thread river channels. Although the channels on Mars are observable, we do not fully understand the morphology of the channels and how they differ from terrestrial alluvial rivers. Alluvial river channels are formed through the interaction between the sediment, which forms the channel boundaries, and the fluid, which transports the sediment. In most terrestrial systems, the fluid is water. However, on planetary bodies like Mars, with an abundance of salt minerals, a primary fluid could have been denser, more viscous brine. If brine formed the ancient channels on Mars, then the resulting morphology could be different than terrestrial counterparts. For example, in equilibrium channels, the higher density of the brines would cause shear stress to increase leading to channel shallowing. This could cause channel widening for an equivalent discharge. We hypothesize that the channels on Mars are wider due to the presence of flowing brines. To test this hypothesis, we created small, single-thread channels at equilibrium in the lab. Equilibrium for a channel is defined when the amount of sediment entering the system is equal to the amount of sediment moving out. In the case of our experiments, the channel is at equilibrium when the sediment stops moving completely. To measure the changes in channel morphology, we created small single-thread channels on a water table and tested variable fluid densities. We documented the results with time-stepped photographs and a precision slope measuring device. The results indicate that the differing viscosities and densities lead to changes in channel morphology. The differing channel morphology could mean an overestimation of discharge by an order of magnitude leading to an overestimation of the volume of water during Martian history. This work will lead to a greater understanding of the paleoclimate of Mars. In addition, the results will contribute the greater field of extraterrestrial fluvial geomorphology.