Volcanism on Io: Emplacement of Lava Flow Fields

Io is the most volcanically active body in the Solar System, with a diverse range of styles of effusive and explosive eruptions. Eruption styles familiar to terrestrial volcanologists have been identified, including insulated pahoehoe-like lava flows, active lava lakes, and flood basalt-like flows which emanate from long fissures (these eruptions often begin with extensive lava fountains; e.g., Pillan, Tvashtar). However, despite a global eruption rate of lava and sulphurous materials exceeding 430 km³/yr, only a few structures resemble canonical shield volcanoes. For example, three such shield-like features are seen at Zamama. From these three cones emanate 15 lava flows, some of which were emplaced during the Galileo mission. Instead, much of Io's volcanic activity is confined to paterae, caldera-like depressions mostly set in flat plains, and flow fields. The largest patera is Loki Patera, which is nearly 200 km across. Io's active flow fields often cover thousands of km² (Prometheus's flows cover >6300 km²) and the largest (such as Lei Kung Fluctus) exceed 1.25 x 10⁵ km². At the other end of the activity scale, no small-scale cinder cones have been identified, probably because little of Io has been imaged at high spatial resolutions. Subtle thermal detections in low resolution Galileo NIMS data indicated the presence of small volcanic centres which were later identified in higher resolution NIMS data; however, these areas were not imaged at visible wavelengths at high spatial resolution. Alternatively, it may be that the eruption of low viscosity, possibly superheated lavas are not conducive to the formation of cones or shields, instead favouring the emplacement of long flows.

This work was performed at the Jet Propulsion Laboratory-California Institute of Technology, under contract to NASA.