Color and morphology of lava flows on Io

Analyses of color and morphologic changes in Voyager images of lava hows on Io were conducted to extend previous flow studies to additional volcanoes in preparation for comparison to Galileo data. Blue and orange filter image s of Atar, Daedalus, and Ra Paterae were examined to identify systematic do wnflow decreases in blue/orange reflectivity suggested in earlier studies a s diagnostic of color changes in cooled sulfur flows. Analyses of the color and morphology of 21 lava flows were conducted at these volcanoes, with ad ditional morphologic analysis of lava flows at Agni, Masaaw, Mbali, Shoshu, and Tales Paterae. A total of 66 lava flows of up to 245 km in length were mapped to identify morphologic changes consistent with the theologic chang es expected to occur in sulfur flows. Although downflow color changes are o bserved, the trends are not consistent, even at the same edifice, Individua l flows exhibit a statistically significant increase in blue/orange ratio, decrease in blue/orange ratio, or a lack of progressive downflow color vari ation. Color changes have similar magnitudes downflow and across how, and t he color ranges observed are similar from volcano to volcano, suggesting th at similar processes are controlling color ratios at these edifices. In add ition, using flow widening and branching as an indicator of the low viscosi ty exhibited by sulfur cooling from high temperatures, these flows do not e xhibit morphologic changes consistent with the systematic behavior expected from the simple progressive cooling of sulfur. (C) 2000 Academic Press.