NEW EVIDENCE FOR EXTRAORDINARILY RAPID CHANGE OF THE GEOMAGNETIC-FIELD DURING A REVERSAL

Palaeomagnetic results from lava flows recording a geomagnetic polarit y reversal at Steens Mountain, Oregon suggest the occurrence of brief episodes of astonishingly rapid field change of six degrees per day. T he evidence is large, systematic variations in the direction of remane nt magnetization as a function of the temperature of thermal demagneti zation and of vertical position within a single flow, which are most s imply explained by the hypothesis that the field was changing directio n as the flow cooled.