The formation mechanism of long run-out landslides on planetary bodies

Landslides are not only an important landscape-forming process on solid bodies throughout the Solar System, but on Earth also represent a natural hazard to life and infrastructure. The mechanisms responsible for the onset and flow of long run-out (typically tens of km) landslides are particularly poorly understood. Numerous methods have been proposed to explain long run-out landslide formation, including, but not limited to: basal fine powders, interstitial fluids, pore fluid pressure, air pockets, steam generation and thermal pressurisation, frictional melts, lubrication, fluidization and dynamic fragmentation.

On Earth, fieldwork allows the in situ investigation of long run-out landslide deposits, which can reveal important insights into the formation mechanism. The slipping zone, or basal plane, of large landslides that accommodates much of the slip displacement is, in many cases, saturated with fluid. The amount of pore fluid pressure can lower the apparent friction of the sliding mass by carrying some of the overburden and reducing the effective stress. Frictional heating and chemical reactions of materials in the landslide slip zone can also lead to pressurization of the pore fluid along the shear zone and reduce the frictional resistance to sliding, by decomposing or dehydrating slip zone material and produce overpressured fluids. This chemical-thermal-poro-mechanical process can lead to extremely high sliding velocity (10-100 m/sec) and can explain the anomalously large runouts. For example, recent studies showed that at the Heart Mountain landslide, the largest sub-aerial landslide on Earth, shear heating at high slip velocities could have caused thermal decomposition and the release of carbon dioxide, which allowed catastrophic slip even on a low angle detachment surface. However, investigating these deposits in the rock record on Earth can be hampered by active geological processes driven by plate tectonics. Therefore it is useful to use other planetary bodies, where deposits have been better preserved due to lower rates of geological activity.

On Mars, there are a large number of long run-out landslides that suffer from a similar uncertainty in formation mechanism , but which are also important in dating key geological processes. Some studies have proposed dehydration controls on the initiation and mechanics of enormous Martian landslides. The scale of such landslides can be seen in Valles Marineris, Mars. On the Moon, a long run-out landslide, thought to be triggered by ejecta from the distant Tycho impact event, has been used as a key calibration point in age dating planetary surfaces through crater size-frequency analysis. This project will address the question of how long run-out landslides initiate and propagate on Earth, the Moon and Mars. This will involve a combination of in situ analysis for terrestrial deposits, and the latest high-resolution remote sensing data (e.g. LROC, HiRISE) for the Moon and Mars, as well as developing. Co-supervisor Schmitt also carried out fieldwork at one of the study landslides in the Taurus-Littrow valley on the Moon during the Apollo 17 mission.