An apparatus was built in conjunction with the transparent anvils drop weight machine to view the events occurring during the formation, growth, and collapse of vapour cavities in thin liquid layers. During the collapse phase, several mechanisms operate, namely: proportional shrinkage, volume jetting, surface jetting and secondary cavitation, which can be attributed to features of the liquid flow under compression. Localized flow in the bodies of the liquid surrounding the cavities drives the proportional shrinkage (in which the cavities roughly retain their shapes); the pressure or shock waves propagation and reflection at the cavity interfaces drive the volume jets; the interaction of the release or rarefaction waves with the pressure/shock wave itself seems to initiate the secondary cavitation and the surface jets seem to be caused by the variations of the vertical distribution of the horizontal flow velocity during the transition from the tensile to the compression phase. A simple model which considers the liquid a perfectly plastic material and assumes a very rapid rate of vapour condensation fits the experimental results throughout most of the collapse process. It seems that in the final stages of the collapse the rate of condensation is not fast enough and the model is not valid there. Further studies should be carried out to better quantify the various mechanisms observed.