Several analyses of the impact cratering record on Venus have concluded that 80% of Venus was resurfaced sometime in the last 300 m.y.--700 m.y. The cratering record further indicates that the resurfacing took place over a 30 m.y--100 m.y. interval. Since this period, there has been little large scale tectonic activity on Venus. This study proposes that such behavior may result from the interaction of phase change induced avalanches with a non-Newtonian lithosphere. The mechanism proposed here suggests that because of non-Newtonian rheology, the Venusian lithosphere becomes highly mobile during brief periods when avalanches occur. Afterwards, due to the reduction in stress levels, the lithosphere becomes rigid and large scale tectonics ceases. ¿ American Geophysical Union 1996