It is well known that screw dislocations are step sources that allow crystals to grow at low driving forces. Growth is accelerated at the outcrop of a screw dislocation generating a spiral hillock. This makes the intersection of a screw dislocation and a crystal surface a so-called velocity source. In this paper the interaction between dislocation growth, 2D-nucleation and misorientation step flow is investigated for a wide range of driving forces by means of Monte Carlo simulations of growth of the Kossel (100) surface. The interactions between the different growth mechanisms are shown to agree with a general model for velocity source behavior, which allows for a simple analytical expression of the growth rate. This expression can be used in a continuum description of crystal growth. Finally, dislocation etching is studied and compared with dislocation growth.