Sulphur flows on Io

Voyager 1 close-encounter photomosaics have clarified both the coloration of Io and its surface variation. These colour patterns seem explicable in terms of liquid sulphur produced in ionian volcanoes and solfataras and quenched at Io ambient temperatures approximately equal to 135 K. The liquid sulphur flow fronts and frozen rivers which appear in the Voyager images are discussed. It is argued that the volcanic deposition rates and the vapour pressure over sulphur melts are both consistent with the notion that the surface of Io changes significantly in geologically very short periods of time. (UK)