- It is well-known that high-Mach number shocks are nonstationary. The shock front steepens and unsteepens quasiperiodically, and some shocks even reform. It is widely believed that the typical timescale of this process is of the order of the ion gyroperiod, so that electrons feel a quasistationary electric field. Electrons, which cross the shock in the adiabatic regime during the unsteepening phase, may become demagnetized in during the shock steepening. Thus, the electron heating regime may be time dependent in high-Mach number shocks and bursty nonadibatic heating may coexist with adiabatic heating. The downstream electron distribution would be a mixture of nonadiabatically and adiabatically heated electrons.