Volcanic Activity on Io during 1987--1992:

Over the past 6 years we have conducted an extensive monitoring program of Io at near infrared wavelengths, in order to determine the location, frequency, and duration of the volcanic activity on this satellite of Jupiter. The observations were obtained at the Wyoming 2.3-m telescope using a near-infrared speckle interferometry system that provides standard photometry and in addition can locate bright hotspots on the disk of the satellite. Most observations were made at a wavelength of 4.8 ¯m. In this paper we concentrate primarily on analysis of the photometric data. The photometry provides a clear record of the variable activity at Loki. This source seems to brighten every couple years, and remains in the active state for a few months. We have seen no activity of comparable brightness at other longitudes. Preliminary models of the activity at Loki suggest that these brightenings correspond to eruption rates and durations similar to that during emplacement of the individual flows whic..