We demonstrate the use of hourly Geostationary Meteorological Satellite (GMS) and NOAA polar-orbiting advanced very high resolution radiometer (AVHRR) satellite images of the June 1991 Mount Pinatubo volcanic eruption plumes in providing details of the timing, changing eruptive style, and umbrella plume movement and dynamics. A chronology of explosive events, which culminated in a >9-hour-long climactic phase on June 15, has been determined from satellite data and favorably compared to ground-based and other ancillary information. Maximum eruption column altitudes of 40 km and column-top undercooling in excess of 55 ¿C below the ambient atmosphere occurred during the climactic phase. Phases dominated by Plinian versus coignimbrite eruptive plumes can be distinguished on the images. Analysis of the spreading umbrella plume during the climactic phase suggests that over the first 4--5 hours the plume spread laterally as a gravitational intrusion before becoming advected in the ambient winds. We compare the rate of plume growth to a model of a radially symmetric, continuously fed intrusion to describe the motion. The rate of plume growth shows good agreement with this simple model for the first 4--5 hours. From column-top heights we determine eruption rates and obtain an independent estimate of the total volume of magma erupted from June 12--16 of ~5.5 km3 dense rock equivalent (DRE), in good agreement with an independent estimate of the total eruptive volume made from deposits on land and submarine ash fall of up to 5.3 km3 DRE. We also show that secondary explosions in the Pinatubo ignimbrite deposits produced ash plumes reaching altitudes as high as 19 km in September 1991. This study indicates that realistic interpretation and monitoring of major eruption plumes can be accomplished by analysis of high temporal resolution satellite data. ¿ American Geophysical Union 1996