Rippled metallic surfaces have been produced as a result of ballistic impact as well as the movement of high-pressure (explosive) gas over a metal plate. Such loading conditions produce a strong shock wave. Under the high pressure, metal plate surfaces are plastically deformed and sometimes are welded together. These welds are sometimes associated with a wavy (rippled) interfacial disturbance. There is no metallurgical evidence for the formation of a fluid jet. In addition to the incident and reflected wave due to impact, a Mach stem (wave) produced by acoustic focusing sweeps along the plate interface.