Comparison of Grainflow Activity on Earth and Mars Utilising 3D Microscale Airflow Modelling

Abstract

Dune migration is accomplished by individual grainflows that redistribute
sediment downslope, locally advancing the slipface. As grainfall and grain saltation over the dune brink restores the slope, subsequent grainflows may take place. The frequency in which grainflows occur is dependent on sediment availability, sediment flux, and the wind regime of the aeolian environment. Slipface dynamics have been the focus of many terrestrial aeolian studies aiming to better understand the mechanisms of dune migration using a variety of approaches including wind tunnel experiments, airflow modelling, and field observation. Until recently, the study of slipface dynamics was confined to Earth due to lack of in situ observations on Mars. In December 2015, the Mars Science Laboratory Curiosity Rover visited a martian dune and collected data on the local wind regime, aeolian sediment characteristics, and high resolution images of
the dune slipface. This new data opened a new avenue for aeolian research, making it possible to directly compare terrestrial and martian dune slipface dynamics.
This study uses terrestrial field observations from the Maspalomas dune field in
Gran Canaria, Spain as a Mars analog to the grainflows imaged by Curiosity on Mars on the Namib dune. The Earth-based research is comprised of video documentation of the dynamics of grainflows and a series of ground-based laser scans that captured the morphometric characteristics of grainflows, including morphology, thickness, and area. These observations are compared to the martian slipface to interpret the grainflow activity preserved on the dune. These interpretations augmented by Computation Fluid Dynamics Modelling at the dune-scale to investigate the influence of the local martian wind regime on aeolian features and sediment transport.
The results demonstrate that similar aeolian slipface processes are operating on
Earth and Mars. Due to Mars’ low density atmosphere, wind speeds must be
significantly greater to initiate grain movement and therefore, the Namib dune is likely subject to short-term intermittent seasonal aeolian activity. Modelling results suggest that there are limited times during the martian day and year when sand grains are mobilised and slipface advancement may largely be confined to the spring season.

Date of Award	Jun 2018
Original language	English
Supervisor	Andrew Cooper (Supervisor) & Derek Jackson (Supervisor)