The trough system of Valles Marineris, Mars contains numerous landslides in the large relief exposures (up to 8 km) of basaltic wall rock and soft interior layered deposits (ILDs). Eleven landslides, including eight circular failures, were mapped in the ILDs. Two wall rock landslide complexes and four ILD landslides were modelled using limit-equilibrium slope stability analysis to evaluate the mechanisms of slope failure. Wall rock landslide complexes in the Ophir and Hebes Chasmata required artesian fluid pressures of at least 41% of overburden pressure or ground accelerations of at least 0.19 Mars g for failure. Agreement between modelled and observed failure surface geometries and the difficulty of generating artesian pressures at a regional topographic high indicate that ground shaking from Marsquakes or impacts most likely triggered the modelled wall rock landslides. Triggering mechanisms, such as ground acceleration or fluid pressure, were also necessary for most other landslides in Valles Marineris wall rock. Given minimum rock mass strengths, ILD landslides in the Hebes and East Candor Chasmata did not require triggering mechanisms; thus, landslides in ILDs may be a result of gravitational, fluid, or seismic loading.