Theses defended

2020 2019 2018 2017 2016 2015



Maï BORDIEC - 15th December

"Formation of topographic waves by mass transfers and diffusion in turbulent flowing fluids"

Interactions between fluid flows and solid substrates exposed to mass transfers (sublimation or condensation for ice and dissolution or precipitation for rocks) can lead to the shaping of spatially organized topographic patterns. We call them “solid bedforms”. This thesis focuses on a specific class of solid bedforms: “transverse linear waves”. Morphological characterization and constraints on the environmental conditions in which these transverse linear waves develop are obtained from the analysis of terrestrial and planetary examples. Their formation, which results from a positive feedback between the flow and the topography, is modeled. To study this instability, a linear stability analysis is performed and highlights a preferential mode for their growth. Three scaling laws are derived from this analysis and relate the geometrical and kinematic characteristics (wavelength, migration velocity, time of formation) of the waves to the environmental conditions (viscosity, speed flow, ablation rate). The laws are in good agreement with the observational data: these waves are thus convenient geomorphic markers for various predictions, in glaciology, geomorphology, karstology and planetology.

Sneha SINGH - 20th November

"Wavefield gradients and small-scale heterogeneities"

Since all seismic sources produce not only translations but also its gradients, i.e strains and rotations; all three motions are equally crucial in seismology. Only with the measurement of all these motions can ground motion be completely accessed.
Unlike translations however, strains and rotations are shown to be affected by local small-scale heterogeneities, such as geological inhomogeneities, surface topographies and cavities. In this work, we study the effect of small-scale heterogeneities on wavefield gradients in the context of both forward and inverse problem.

Maxime PINEAU - 5th November

"Investigation of near-infrared signature properties of opaline silica and kaolinite for interpreting their geological origin on Mars"

Alteration minerals are key objects to understand the geological history of the planetary bodies’ surfaces. In this work, we studied the near-infrared spectroscopic properties of opaline silica and kaolinite in order to constrain the surface paleoclimatic conditions at the surface of Mars during the past. A preliminary geomorphologic study of opal-bearing deposits on Mars shows four types of deposits: aeolian deposits, hydrothermal deposits, alluvial fan/fan delta and bedrock. Spectroscopic criteria, distinguishing continental weathering and hydrothermal opals, show that aeolian deposits are relicts of hydrothermal deposits. Other deposits are of weathering origin, except hydrothermal deposits that have a spectral signature consistent with low-temperature hydrothermal activity. Near-infrared properties of kaolinite are proxies of its crystalline degree. Poorly ordered kaolinites are exclusively of continental weathering origin while well-ordered kaolinites can form by either hydrothermalism or continental weathering.