A lot of information on impacts of solid bodies on planets
has been extracted from remote observations of impact craters
on planetary surfaces; experiments however with
large enough impact energies as compared to the energy stored in
the ground are difficult. We approach this problem by
downscaled experiments and by corresponding discrete particle numerical
simulations: The idea is to fully  decompactify very
fine sand which then at impact of a steel ball behaves fluid-like.
The series of events is as follows: On impact of the ball, sand is
blown away in all directions (``splash'') and an impact crater
forms. When this cavity collapses, a granular jet emerges and
is driven straight into the air.
A second jet goes downwards into the  air bubble entrained
during the process, thus pushing surface material deep into the ground.
The entrained air bubble rises slowly towards the surface,
causing a granular eruption.
In addition to the experiments and discrete particle
simulations, we present a simple continuum theory to account
for the void collapse leading  to the formation of the upward
and downward jets. We show that the phenomenon is robust
and even works for oblique impacts: the upward jet is then
shooting  backwards, in the direction where the projectile came from.