During the periods after the maximum phase of geomagnetic storms on 2 April 1972 a broadband VLF emission burst has been observed by the equatorially orbiting satellit S3-A (Explorer 45) along its inbound plasmapause crossings. The frequency band broadening takes place just outside of the nighttime plasmasphere, where the density of cold plasma has been known to be very low during the later phase of a geomagnetic storm. Instead of the gradual broadening of several hours duration, a burst type braodening of VLF emission lasting less than ten minutes was observed in the similar location. The magnetic field component of this emission is very weak and the frequency spreads below the local half electron cyclotron frequency. Corresponding enhancement of the anisotropic ring-current electrons is also very sudden and limited below the order of 10 keV without significant velocity dispersion, in contrast to the gradual broadening events. The cause of this type of emission band spreading can be attributed to the generation of the quasi-electrostatic whistler mode emissions of short wavelength by hot bi-maxwellian electrons surging into the domain of relatively low density magnetized cold plasma. The lack of energy dispersion in the enhanced electrons indicates that the inner edge of the plasma sheet, the source of these hot electrons, is not far from the location of this event.