A model of giant edge localized modes in tokamaks is developed. The theory of self-sustained turbulence of a current-diffusive ballooning mode is extended. A bifurcation from the H mode to a third state with magnetic braiding, the M mode, is found to occur if the pressure gradient reaches a critical value. Nonlinear excitation of magnetic perturbation takes place, followed by catastrophic increase of transport. With backtransition to the $H\left(L\right)$ mode, a new hysteresis is found in the gradient-flux relation. The process then repeats itself. Avalanche of transport catastrophe across the plasma radius is analyzed.