Indentation experiments were performed with a pyramidal Vickers indenter on glass samples to observe the dynamic process of indentation. Successive picture images of indentation were taken by a CCD camera through a microscope. The change in diagonal length of the indentation was measured as a function of time of the order of several tens of milliseconds. The results show that the initial process of indentation is highly dependent on the collision velocity of the indenter when it comes into contact with the sample. Higher collision velocities yield larger rates of initial increase in diagonal length. An empirical equation was obtained that is similar to a visco-elastic Voigt model. It is suggested that local heating due to friction between the indenter and the sample or adiabatic compression reduced the viscosity of the sample material. The dynamic effect observed may be a cause of the change in resistance that is seen in the rate-dependent rock friction. ¿ American Geophysical Union 1995