Two new, rare, high-effusion outburst eruptions at Rarog and Heno Paterae on Io

Observations obtained with the near-infrared camera NIRC2, coupled to the adaptive optics system on the 10-m W.M. Keck II telescope on Mauna Kea, Hawaii, on 15 August 2013 at ~15:30UT revealed two large 'Outburst'-class volcanic eruptions on Io. Follow-up observations five days later showed that both eruptions had substantially faded. The most energetic eruption was at Rarog Patera, at a location near 305°W, 42°S; a smaller one occurred further south at ~310°W and ~57°S, close to Heno Patera. Total radiant fluxes at Rarog Patera on August 15 were of order ~500GW/sr/μm at wavelengths between 2 and 4μm, and close to 250GW/sr/μm at 1.6μm, indicative of an effective temperature of ~1040K over an area of ~120km2, and a total thermal emission of nearly 8TW. At Heno Patera the 4-μm flux measured ~250GW/sr/μm, and ~90GW/sr/μm at 2.2μm, suggestive of an effective temperature of ~720K over an area of more than 300km2, and a total thermal emission of ~5-6TW. Fits of the Davies (Davies, A.G. [1996]. Icarus 124(1), 45-61) Io Flow Model indicate that these two eruptions are vigorous and the exposed surfaces are mostly very young, no older than 4-5min at Rarog Patera and a few hours at Heno Patera. The model fits suggest that in both locations lava fountaining is taking place, a highly-energetic style of volcanism. Using follow-up observations taken between August 20 and September 7 we estimate peak effusion rates between 5×104 and 105m3/s