  We present results from three-dimensional numerical simulations of the
dynamics of SN-driven bubbles as they propagate through and escape the grasp of
subgalactic halos with masses M ~ 10^8 Msun at redshift z=9. The hydrodynamic
simulations use a nested grid method to follow the evolution of explosive
multi-SN events operating on the characteristic timescale of a few x 10^7 yr,
the lifetime of massive stars. The results confirm that, if the star formation
efficiency of subgalactic halos is close to 10%, a significant fraction of the
halo gas will be lifted out of the potential well (`blow-away'), shock the
intergalactic medium, and pollute it with metal-enriched material, a scenario
recently advocated by Madau, Ferrara & Rees (2001). The volume filling factor
of the ejecta is close to unity. Depending on the stellar distribution, we find
that less than 30% of the available SN energy is converted into kinetic energy
of the blown away material, the remainder being radiated away. It appears that
mechanical feedback is less efficient than expected from simple energetic
arguments, as off-nuclear SN explosions drive inward-propagating shocks that
tend to collect and pile up cold gas in the central regions of the host halo.
Low-mass galaxies at early epochs may survive multiple SN events and continue
forming stars.
