GEOLOGY AND TOPOGRAPHY OF RA PATERA, IO, IN THE VOYAGER ERA - PRELUDETO ERUPTION

Voyager era stereo images are used to map the geology and topography o f Ra Patera (a major active volcanic center and possible site of sulfu r eruptions on Io). The summit of Ra Patera reaches only similar to 1 km above the surrounding plains. pre-Voyager-era lava flows occur on s lopes of 0.1-0.3 degrees, comparable to the lunar mare. These flows we re emplaced at either low viscosities, high eruption rates, or both. A 600-km-long ridged mountain unit (rising to similar to 8 km near Cara ncho Patera) forms a 60 by 90 km wide plateau similar to 0.5 km high 5 0 km east of Ra Patera. The new lava flows observed by Galileo flowed around the southern edge of this plateau.