  We report on specific effects of collective scattering for a cloud of heavy
impurities exposed to a gas stream. Formation is presented of a common density
perturbation and shock waves, both generated collectively by a system of
scatterers at sudden application of the stream-inducing external field. Our
results demonstrate that (i) the scattering of gas stream can be essentially
amplified, due to nonlinear collective effects, upon fragmentation of a solid
obstacle into a cluster of impurities (heterogeneously fractured obstacle);
(ii) a cluster of disordered impurities can produce considerably stronger
scattering accompanied by enhanced and accelerated shock wave, as compared to a
regularly ordered cluster. We also show that the final steady-state density
distribution is formed as a residual perturbation left after the shock front
passage. In particular, a kink-like steady distribution profile can be formed
as a result of shock front stopping effect. The possibility of the onset of
solitary diffusive density-waves, reminiscent of precursor solitons, is shown
and briefly discussed.
