  We discuss results from 3+1-D numerical simulations of SU(2) Yang--Mills
equations for an unstable Glasma expanding into the vacuum after a high energy
heavy ion collision. We expand on our earlier work on a non-Abelian Weibel
instability in such a system and study the behavior of the instability in
greater detail on significantly larger lattices than previously. We establish
the time scale for the onset of the instability and demonstrate that the growth
rate is robust as one approaches the continuum limit. For large violations of
boost invariance, non-Abelian effects cause the growth of soft modes to
saturate. At late times, we observe significant creation of longitudinal
pressure and a systematic trend towards isotropy. These time scales however are
significantly larger than those required for early thermalization in heavy ion
collisions. We discuss additional effects in the produced Glasma that may speed
up thermalization.
