Effects of lava heating on volatile-rich slopes on Io

Abstract:

Jupiter’s moon Io is characterized by vigorous and diverse silicate and sulfurous volcanism. Volcanotectonic depressions called paterae often host eruptive activity including lava lakes and confined flows. Paterae resemble terrestrial calderas, but may have a distinct origin. Keszthelyi et al. [2004, Icarus 169, 271-286] suggested that they are depressions formed when the heat from a sill melts and sublimates a crustal layer rich in volatile S and SO₂. A prediction of this model is that the near-vertical, 1-2 km patera walls are rich in volatiles. Here we explore the consequences of this hypothesis using a numerical model for the heating of volatile slopes. The heat conduction equation is solved in one dimension for a sloped surface with inputs from time-varying solar and Jovian radiation as well as radiant heat from a lava flow at the base of the slope. Two end-members are considered: (1) an instantly-emplaced infinitely wide flow that cools rapidly, and (2) a steady-state lava surface characterized by some resurfacing or turnover timescale. Temperature-dependent thermophysical properties and latent heat effects are included.

We investigate the heating of steep (70 degree) S- and SO₂-rich slopes. Within a nominal parameter range early in the instantly-emplaced lava flow scenario, S-rich slopes briefly reach the melting point. However, this is unlikely to be realistic. The steady-state case results in heating of the walls, and can undergo significant sublimation and even melting if the turnover time is short (hours). In either case, lava heating is likely to soften sulfur-rich walls to a depth dependent on the heating timescale, which could destabilize slopes that would otherwise be stable. An SO₂-rich slope under the same conditions undergoes enough sublimation to cause meters of wall retreat per year, and possibly serve as an important local source of SO₂ vapor.

This work is funded by NASA PGG grant #NNH14AX97I.