We present a method to determine the energy-momentum tensor density created between two colliding nuclei at very high energies shortly after the collision. We assume a color field building up between the nuclei that rapidly decays into a quark gluon plasma. The field is induced by effective color charges in the nuclei and can be approximated by solving the classical QCD equations of motions for small times. Coherence arguments and energy-momentum conservation in the system, including the deccelerating nuclei, lead to constraints on the local energy density and pressure of the plasma phase. Our results can directly serve as initial conditions of a further hydrodynamic evolution of the system.