The results of investigations of nonlinear tearing‐mode dynamics in reversed field pinch plasmas are described. The linear instabilities have poloidal mode numberm=1 and toroidal mode numbers 10≲n≲20, and the resonant surfaces are therefore in the plasma core. The nonlinear dynamics result in dual cascade processes. The first process is a rapidm=1 spectral broadening toward highn, with a simultaneous spreading of magnetic turbulence radially outward toward the field‐reversal surface. Globalm=0 perturbations, which are driven to large amplitudes by them=1 instabilities, in turn trigger them=1 spectral broadening by back coupling to the highern. The second process is a cascade toward largemand is mediated bym=2 modes. Them=2 perturbations have the structure of localized, driven current sheets and nonlinearly stabilize them=1 modes by transferringm=1 energy to small‐scale dissipation. The calculated spectrum has many of the qualitative features observed in experiments.