earth-based infrared studies in the 1980s and 1990s shifted the paradigm from one of primarily sulfur volcanism to one where silicate volcanism dominates, and sulfur acts in a secondary role. in 1986, measurements of a bright eruption on io's leading hemisphere revealed temperatures of at least . this is higher than the boiling point of sulfur (), indicating a silicate composition for at least some of io's lava flows. similar temperatures were also observed at the surt eruption in 1979 between the two "voyager" encounters, and at the eruption observed by witteborn and colleagues in 1978. in addition, modeling of silicate lava flows on io suggested that they cooled rapidly, causing their thermal emission to be dominated by lower temperature components, such as solidified flows, as opposed to the small areas covered by still molten lava near the actual eruption temperature.