  Landslide deposits often exhibit surface features, such as transverse ridges
and X-shaped conjugate troughs, whose physical formation origins are not well
understood. To study the deposit morphology, laboratory studies typically focus
on the simplest landslide geometry: an inclined plane accelerating the sliding
mass immediately followed by its deceleration on a horizontal plane. However,
existing experiments have been conducted only for a limited range of the slope
angle $\theta$. Here, we study the effect of $\theta$ on the kinematics and
deposit morphology of laboratory landslides along a low-friction base, measured
using an advanced 3D scanner. At low $\theta$ (30{\deg}-35{\deg}), we find
transverse ridges formed by overthrusting on the landslide deposits. At
moderate $\theta$ (40{\deg}-55{\deg}), conjugate troughs form. A Mohr-Coulomb
failure model predicts the angle enclosed by the X-shaped troughs as
90{\deg}-$\phi$, with $\phi$ the internal friction angle, in agreement with our
experiments and a natural landslide. This supports the speculation that
conjugate troughs form due to failure associated with a triaxial shear stress.
At high $\theta$ (60{\deg}-85{\deg}), a double-upheaval morphology forms
because the rear of the sliding mass impacts the front during the transition
from the slope to the horizontal plane. The overall surface area of the
landslides increases during their downslope motion and then decreases during
their runout.
