Hybrid (particle ion, massless fluid electron) simulations are carried out in one and two spatial dimensions to show that the supercritical quasi-parallel shock is not steady. Instead of a well-defined narrow transition region (shock ramp) between upstream and downstream states that remains at a fixed position in the flow, the ramp periodically steepens, broadens, and then re-forms upstream of its former position. During part of the re-formation cycle, the number of ions backstreaming from the shock increases to a significant fraction (up to 40%) of the incoming ions. This dense ion beam then couples to the incident ions to form a heated region, the leading edge of which becomes the new shock ramp. Two-dimensional simulations demonstrate that this process is not a consequence of restricting the calculations to one spatial dimension and show that the re-formation cycle is not in phase along the shock surface, although the surface itself remains fairly laminar. Generally, the downstream wave turbulence is comparable in all three magnetic components (unlike one dimensional where Bn=const) and shows no tendency to be aligned in any particular direction. Both the two-dimensional simulations as well as the one-dimensional runs indicate that the downstream plasma is a complex mixture of regions of merged incident and reflected ion beams. The simulations are consistent with recent observational studies at the quasi-parallel bow shock showing the presence of magnetic pulsations, cold ion beams, and a downstream consisting of alternating regions of low-density hot ions and higher density cooler ions. ¿ American Geophysical Union 1990