  Tsunami waves induced by landslides are a threat to human activities and
safety along coastal areas. In this paper, we characterize experimentally the
waves generated by the gravity-driven collapse of a dry granular column into
water. Three nonlinear wave regimes are identified depending on the Froude
number $\mathrm{Fr}_f$ based on the ratio of the velocity of the advancing
granular front and the velocity of linear gravity waves in shallow water:
transient bores for large $\mathrm{Fr}_f$, solitary waves for intermediate
values of $\mathrm{Fr}_f$, and non-linear transition waves at small
$\mathrm{Fr}_f$. The wave amplitude relative to the water depth increases with
$\mathrm{Fr}_f$ in the three regimes but with different non-linear scalings,
and the relative wavelength is an increasing or decreasing function of
$\mathrm{Fr}_f$. Two of these wave regimes are rationalized by considering that
the advancing granular front acts as a vertical piston pushing the water, while
the last one is found to be a transition from shallow to deep water conditions.
The present modeling contributes to a better understanding of the rich
hydrodynamics of the generated waves, with coastal risk assessment as practical
applications.
