Cavities are present in a wide range of energetic systems by design or mischance. In either case, the presence of a bubble sensitizes the explosive to ignition when it is collapsed by a shock pulse. In this case, the temperature within the cavity is high as well as the collapse being asymmetric. Many authors attribute ignition to the adiabatic heating of the trapped gas. In this work, cavities are created within an ammonium nitrate emulsion matrix. They are large enough to be visualized using conventional optics with a high-speed camera. These relatively large cavities collapse in such a way that the ignition event is controlled by the hydrodynamic pressures generated by the impact of a high–speed liquid jet. It is thought that other mechanisms may dominate at different length–scales.