Defense of thesis “Influence of ice degradation on global landscapes” – Meven Philippe

My thesis aims to gain a new understanding of how ground ice and associated processes influence surface geomorphology on Earth and on Mars. I investigate two landforms: molards and thermal-contraction polygons.
Molards are cones of loose debris found in landslide deposits, indicative of permafrost degradation. I developed a novel photogrammetry system to monitor the shape of molards created in the laboratory setting. This opens the door to future studies that will use molards to better understand the state of mountain permafrost. I also present a study on the potential first martian molards, that provide insights into the ice and water content of the ejecta of Hale crater, as well as on their post-impact evolution.
Ice-wedge polygons are networks of polygonal fractures, which initially form by the thermal contraction of ground ice. Repeated freeze-thaw cycles of water generate different polygon morphologies. Mars has polygons with similar morphologies, but whether liquid water was involved in their formation is still under debate, because liquid water is thought to be unstable under the present martian climate. Hence, I investigate thermal-contraction polygons in Utopia Planitia, and the results suggest that liquid water could have been involved. In parallel, I developed a methodology that uses thermal-contraction polygons to infer the geological properties of their substrate, which gives new constraints on the origin of the terrains in Utopia Planitia.

Date and place : 12 July at 2pm, LPG, Faculty of Sciences, Nantes University

Published on June 16th, 2023