A continuous record of the 80 MHz image and polarization of a type IV solar outburst has been made with the Culgoora radioheliograph from which the magnetic structure of the event can be directly inferred. The first ('moving') part of the event appears beyond the limb as an expanding magnetic arch along which three concentrated sources develop: one unpolarized source near the peak, attributed to synchrotron radiation; and two polarized sources of opposite polarity near the feet, attributed to plasma radiation. The radio-emitting arch appears to lie above an eruptive prominence seen in Hα. The second ('stationary') part is seen later as a separate highly polarized source on the disk above the projected position of the flare that had previously triggered the prominence activity. © 1969 D. Reidel Publishing Company.