  The detection of Ly alpha emission in star-forming galaxies in different
shapes and intensities (always smaller than predicted for case B recombination)
has puzzled the astronomical community for more than a decade. Here we use two
dimensional calculations to follow the evolution of superbubbles and of the H
II regions generated by the output of UV photons from massive stars. We show
the impact caused by massive star formation in the ISM of different galaxies
and we look at the conditions required to detect Ly alpha emission from a
nuclear H II region, and the variety of profiles that may be expected as a
function of time.
