We have observed the sudden and spontaneous evolution of an initially correlated gas of repulsively interacting Rydberg atoms to an ultracold plasma.
By combining optical imaging and ion detection, we access the full information on the dynamical evolution of the system, including the rapid increase in the number of ions and a sudden depletion of the Rydberg and ground state densities. The Rydberg blockade effect is observed to strongly affect the dynamics of plasma formation, and the initial correlations of the Rydberg distribution should persist through the avalanche. This may provide the means to overcome disorder-induced-heating, and offer a route to enter new strongly-coupled regimes.