International Ultraviolet Explorer (IUE) observations of Ganymede demonstrate decade length or less temporal variations at a few discreet trailing side longitude regions. The temporal changes are seen in comparisons of IUE spectra from 1984--1986 with new IUE observations from 1996. Variations are observed on the trailing side associated with the new detection of SO2 frost. A distinctive SO2 frost spectral signature at 0.32 &mgr;m is detected in the 1984--1986 spectra of trailing side regions from 225¿ to 285¿ which are absent in corresponding 1996 measurements. ¿ 1998 American Geophysical Union