During the first few hours after each impact, numerous phenomena were observed with telescopes on Earth, in orbit, and in space. The primary events in that time were: impacts themselves, rise and fall of large plumes of ejected material, and atmospheric waves; also of interest were the characteristic morphologies of fresh sites. Based on timing from Galileo instruments and ground-based observations, the Hubble Space Telescope (HST) recorded actual impact phenomena for fragments G and W, with the A and E impacts occurring just prior to the HST observation window. For these four events, plumes were directly imaged; plume development and collapse correlated with strong infrared emission near the jovian limb, supporting the interpretation that the IR brightness was created by the fall-back of plume material from high altitude (see chapter by Nicholson). For medium-to-large fresh impact sites imaged by HST within a few hours of impact, expanding rings were detected, caused by horizontal propagation of atmospheric waves (see chapters by Ingersoll and Zahnle). Initial site morphology at visible wavelengths was similar for all medium-to-large impacts: a dark streak surrounded by dark material, dominated by a large crescent-shaped ejecta to the southeast. Smaller impact sites typically only showed a dark patch (no ejecta) which dissipated quickly. This chapter summarizes the most recent measurements and interpretations of plumes and fresh impact sites as observed by HST.