  In this Letter, we experimentally investigate the collapse of initially dry
granular media into water and the subsequent impulse waves. We systematically
characterize the influence of the slope angle and the granular material on the
initial amplitude of the generated leading wave and the evolution of its
amplitude during the propagation. The experiments show that whereas the
evolution of the leading wave during the propagation is well predicted by a
solution of the linearized Korteweg-de Vries equation, the generation of the
wave is more complicated to describe. Our results suggest that the internal
properties of the granular media and the interplay with the surrounding fluid
are important parameters for the generation of waves at low velocity impacts.
Moreover, the amplitude of the leading wave reaches a maximum value at large
slope angle. The runout distance of the collapse is also shown to be smaller in
the presence of water than under totally dry conditions. This study provides a
first insight into tsunamis generated by subaerial landslides at low Froude
number.
