Volcanic Activity on Io During the Galileo Era

Galileo's explorations have revealed a remarkable variety of eruptive styles among Io's diverse volcanoes. Activity at hundreds of volcanic centers ranges from dormant through sporadic to continuous over the 20-year period of spacecraft observation. High temperature volcanism is common on Io, suggesting that the lavas are made up of mafic to ultramafic silicates rather than sulfur compounds. Io's largest plumes are driven by SO2 and sulfur-rich gasses vented from the silicate interior that produce prominent red pyroclastic deposits. Red deposits flag the source regions of many other ongoing or very recent eruptions. Smaller plumes are produced near the margins of active lava flows by explosive volatilization of the underlying or surrounding SO2. These plumes produce SO2 snowflakes that mantle existing topography. Io's volcanism drives significant variations in the atmosphere and plasma torus, yet most of the heat loss occurs through lava flows and by the quiet overturning of lava lakes without large-scale explosive activity. Although only a handful of Io's volcanoes have been directly observed to produce explosive eruptions, volcanic resurfacing is efficient enough to erase even small craters from Io's youthful surface.