  Plasma instabilities are parametrically the dominant nonequilibrium dynamics
of a weakly coupled quark-gluon plasma. In recent years the time evolution of
the corresponding collective colour fields has been studied in stationary
anisotropic situations. Here I report on recent numerical results on the time
evolution of the most unstable modes in a longitudinally expanding plasma as
they grow from small rapidity fluctuations to amplitudes where non-Abelian
self-interactions become important.
