Lava Lakes on Io

Calderas are the most ubiquitous volcanic construct on Io's surface. Data from Galileo has shown that many Ionian calderas are active and that activity is often confined to the caldera's interior. We use observations from Galileo's Near-Infrared Mapping Spectrometer (NIMS) to study the thermal emission from several Ionian calderas. Galileo's close fly-bys of Io from 1999 to 2001 have allowed NIMS to image the calderas at high spatial resolution (1-30 km pixel). At these scales, several of the calderas reveal greater thermal emission around the edges, which can be explained as the crust of a lava lake breaking up against the caldera walls. Comparisons with imaging data show that lower albedo areas (which are indicative of young lavas) coincide with higher thermal emission areas on NIMS data. Other calderas, however, show thermal emission and features in the visible that are more consistent with lava flows over a solid caldera floor. Identifying eruption styles on Io is important for constraining eruption and interior models on Io. We will focus on the thermal analysis of NIMS data from the last two successful fly-bys of Galileo, in particular, on observations of the calderas Tupan, Emakong, Gish Bar, Culann, Chaac, and a small caldera near Tohil, and examine the distribution of thermal emission, how it had varied with time, and the implications for eruption styles. The new observations suggest that lava lakes may be common on Io, perhaps much more than on Earth, possibly reflecting differences in volcanic plumbing and magma composition.