From molecular dynamics simulations for up to 2.5 micros, results are reported on structural dynamics in glass-forming metallic Ni(0.5) Zr(0.5) melts at 700 and 785 K. After elimination of high-frequency fluctuations, cascades of atoms and avalanches of atom chains, local in space and time, are identified as complex processes that govern the heterogeneous low-frequency dynamics in sufficiently aged structures near the glass temperature.