The mechanisms for the explosive loss of plasma confinement that occurs in solar flares, magnetospheric sub-storms, tokamak disruptions and edge localized modes remain largely unexplained. Modelling the rapid onset of such events provides a considerable challenge to theory. A possible explanation for these events, nonlinear explosive ballooning, is discussed. In this mechanism a narrow finger of plasma erupts from inside the plasma growing explosively and pushing aside other field lines—the instability spreads from a small region until it disturbs lines across a large section of plasma. The model predicts the observed features of some high β tokamak disruptions.