  We present simulations of the magnetized interstellar medium (ISM) in models
of massive star forming (40 Msun / yr) disk galaxies with high gas surface
densities (~100 Msun / pc^2) similar to observed star forming high-redshift
disks. We assume that type II supernovae deposit 10 per cent of their energy
into the ISM as cosmic rays and neglect the additional deposition of thermal
energy or momentum. With a typical Galactic diffusion coefficient for CRs (3e28
cm^2 / s) we demonstrate that this process alone can trigger the local
formation of a strong low density galactic wind maintaining vertically open
field lines. Driven by the additional pressure gradient of the relativistic
fluid the wind speed can exceed 1000 km/s, much higher than the escape velocity
of the galaxy. The global mass loading, i.e. the ratio of the gas mass leaving
the galactic disk in a wind to the star formation rate becomes of order unity
once the system has settled into an equilibrium. We conclude that relativistic
particles accelerated in supernova remnants alone provide a natural and
efficient mechanism to trigger winds similar to observed mass-loaded galactic
winds in high-redshift galaxies. These winds also help explaining the low
efficiencies for the conversion of gas into stars in galaxies as well as the
early enrichment of the intergalactic medium with metals. This mechanism can be
at least of similar importance than the traditionally considered momentum
feedback from massive stars and thermal and kinetic feedback from supernova
explosions.
