We perform numerical hydrodynamic modeling of various physical processes that can form an HI ring as is observed in Holmberg~I. Three energetic mechanisms are considered: multiple supernova explosions (SNe), a hypernova explosion associated with a gamma ray burst (GRB), and the vertical impact of a high velocity cloud (HVC). We find that multiple SNe are in general more effective in producing shells that break out of the disk than a GRB of the same total energy. Both multiple SNe and single GRBs can produce kpc-sized HI rings in dwarf galaxies, whereas HVCs are much less effective in producing giant HI rings. The results were published in Astronomy and Astrophysics, 2005, 431, 451. The paper in the pdf format can be downloaded here . This research was done in collaboration with Prof. Shantanu Basu.