The evolution of fast magnetosonic waves of high frequency propa-
gating into an axisymmetric equilibrium plasma is studied. By using
the methods of weakly nonlinear geometrical optics, it is shown that the
perturbation travels in the equatorial plane while satisfying a transport
equation which enables us to predict the time and location of formation of
shock waves. For plasmas of large magnetic Prandtl number, this would
result into the creation of sheet currents which may give rise to magnetic
reconnection and destruction of the original equilibrium.