Reconnective annihilation of magnetic field leads to the formation of magnetic flux cells with small scales, followed by enhanced transverse plasmons occurring in a thin current sheet with a very small vertical extent. The analysis here focuses on the nonlinear interaction between the flux and plasmons. The transverse plasmon field is modulationally unstable in the Lyapunov sense. When the initial pumping wave amplitude attains the threshold of instability, this instability occurs with a high growth rate. Nonlinear development of modulational instability eventually results in self-similar collapse, due to nonlinear equilibrium, giving rise to a spatially intermittent, collapsing magnetic flux, very similar to a turbulent pattern. The Maxwell stress tensor from the turbulence flux determines the anomalous magnetic viscosity, i.e. the parameter α. It is shown that the instability is responsible for the alternation of outburst or quiescent states in astrophysical accretion disks. When the instability occurs, the parameter α is large. In the quiescent state, the instability is suppressed, leading to a smaller, collapse-quenching value of α.