Craters on the surface of an yttrium-aluminum garnet crystal plate under irradiation by nanosecond laser pulses with an intensity of 10 9 –10 10 W/cm 2 and a wide (∼500Å) spectrum have been studied. The mechanism of crater formation as a result of plastic deformation of the surface during the laser action has been discussed. The proposed mechanism takes into account specific features of nonlinear effects under the action of a broadband radiation on the medium. In the stimulated Brillouin scattering of pumping radiation, acoustic waves transform into shock waves, on the fronts of which stimulated Raman scattering develops. As a result, crystal lattice defects formed on the shock-wave fronts are dragged in the direction of pumping, which leads to a high-rate deformation of the crystal surface.