Avalanche dynamics on desert dunes: Processes and drivers, from ancient to modern

Project Rationale:

Avalanching is responsible for wind-blown dune migration on Earth and Mars and because avalanches are preserved in dune stratigraphy, they are the most direct way that we can interpret past wind-climate conditions. From the stratigraphic record in ancient and modern dunes, we can observe variability in avalanche deposit thickness, slope and grainsize distribution. Recent evidence from a 5 m barchan suggested avalanche magnitude is driven by grainfall dynamics which link to wind speed [1] and observations of avalanches have been made on a Martian barchan visited by Curiosity [2]. However, evidence is lacking on the extent this theory holds for dunes of different heights and grain size. Without a better grasp of the process-form feedbacks between dune size and avalanche drivers, it is impossible to interpret the ancient wind climates that formed dune environments now preserved in the rock record. Previous attempts to investigate avalanche dynamics have been hampered because slopes are unstable for mounting instruments. This PhD will use the latest technology to measure avalanches remotely and supplement field experiments with laboratory replicates. Ultimately the research outcomes will provide unique, cutting-edge insight into the influence of avalanche dynamics on aeolian dune migration, both modern and ancient.

Methodology:

The principal aim of this project is to examine how driving processes of avalanches are imprinted on dune stratigraphy and in the rock record, and how this process might vary for Mars. This requires a multi-methodological approach. Field evidence of avalanche dynamics will be collected from White Sands National Monument, New Mexico, USA, where preliminary work by supervisor Ewing has shown that avalanche lobe thickness and grainsize distribution change along a downwind transect. Here you will undertake active process measurements, using terrestrial laser scanning (TLS) to characterize avalanche morphology and grainfall zone dynamics, along with sonic anemometry to measure flow and sediment samples for grain size analysis. Field work at Great Sand Dunes National Park, Colorado, will add data from different grain types. Field work will be supplemented by experiments within the new School of Geography and Environmental Science aeolian avalanche slope facility which is capable of replicating and controlling for field slope angle, sediment size and grainfall dynamics. Climate conditions responsible for Jurassic-age avalanches (in Utah) will be reconstructed using TLS and grain size measurements, along with knowledge from the modern field and lab. Curiosity and HiRISE data will be used to measure size and shape of Martian avalanches.

Training:

The INSPIRE DTP programme provides comprehensive personal and professional development training alongside extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial/policy partners. The student will be registered at the University of Southampton and hosted within the School of Geography and Environmental Science at Highfield Campus. The supervisory team are experts in desert landscape processes and together have extensive experience in undertaking effective field campaigns with high resolution process-form measurements. Full training will be provided in the use of TLS [1], 3D sonic anemometry [3], sediment transport measurements, grain size analysis, remote sensing techniques, ancient and modern environment interpretations [2], field skills, laboratory experimental avalanche slope techniques and large data set processing and analysis.