The processes leading to permanent deformation when two bodies make contact are important in adhesion, wear, and tribology. We present nanoindentation results for GaAs showing that impact kinetic energies of only a few eV can lead to a dramatic reduction in the load required to cause permanent deformation when compared to the load required for impact energies of less than 1 eV. We explain this extreme sensitivity to the initial contact in terms of atomic size asperities which must be deformed if defects are to be generated on impact. Lower kinetic energies do not destroy the asperities, and dislocations must be nucleated later in the indentation cycle. ©1996 American Institute of Physics.