In 1991 we organized a campaign of observation of mutual eclipses and occultations between the Galilean satellites. This paper presents the results obtained at the European Southern Observatory from the observation of mutual events involving Io. We analyze the infrared observation of the occultation of Io by Europa made with a 1-m telescope of February 20, 1991. During the observation of this occultation two volcanoes were occulted by Europa and their signatures have been recorded at 3.8 μm. The same observation was simultaneously made with the ESO 50-cm telescope with the v Strömgren filter. We used this to derive corrections for the ephemerides during the event thanks to a fit of a new photometric model and also to obtain measurements of the positions of hotspots on Io's visible surface. Similarly, a model including the thermal emission of the volcanoes permits a close representation of the infrared lightcurve and provides physical parameters related to the two volcanoes Loki and Pele. © 1992.