Variability and geologic associations of volcanic activity in 2001–2016

Since the end of the Galileo epoch, ground-based observations have been crucial for the continued monitoring and characterization of volcanic activity on Jupiter's moon, Io. We compile and analyze observations from the Keck and Gemini North telescopes between 2001 and 2016, including new and published observations from 2003, 2004, 2005, 2007, 2008, 2009, 2011, 2012, 2013, and 2016. A total of 88 distinct hot spot sites were detected over the 15-year period, 82 of which were detected multiple times, and 24 of which were not detected by Galileo at thermal infrared wavelengths (1–5 µm). A variety of analytical methods are utilized to investigate the detections of active volcanism as a surface expression of interior heating. Geologic associations of hot spots, including patera type, lava flow type, and proximity to mountainous regions, are made using the USGS-published global geologic map of Io (Williams, 2011). We also provide a summary of outburst-scale events, along with the slightly less bright but more frequent, mini-outbursts described by de Kleer and de Pater (2016a). We investigate the spatial distribution of volcanic activity on Io using nearest neighbor, mean pairwise spacing, and mean latitude statistics with various classification schemes. The analysis confirms previous findings in that the heat dissipation appears to be primarily concentrated in the asthenosphere resulting in a high time-averaged surface heat flux at low latitudes. Our observations show significant spatial deviations do exist from the asthenosphere heat dissipation model while also suggesting a deeper source of magma ascent to be present as well, supporting conclusions from previous analyses of primarily spacecraft data (Veeder et al., 2012; Hamilton, 2013; Davies et al., 2015). From a temporal perspective, there are signs of significant variations in the distribution of global heat flux, as volcanoes undetected, and probably dormant, during the Galileo encounters subsequently erupted and remained active during our observations. We also use the on 3.8-µm radiant intensity timelines of individual hot spots, along with the distribution of extensive lava fields in relation to detected activity, as a means to investigate possible connections between hot spots and short timescale, spatio-temporal variations in the global heat flux distribution. We conclude that while the global heat flux distribution remains relatively constant over decadal timescales, there is evidence that significant deviations do occur potentially as a result of mountain forming processes or triggering mechanisms between eruptions.