| Summary: | The return of the first Voyager images of Io in 1979 provoked a controversy over the
importance of sulfur versus silicate volcanism in resurfacing the satellite. The debate
involves both the strength of crustal material as well as the mode of mass and heat
transport to the surface of Io. The dynamics of sulfur magma transport will depend
upon the properties of liquid sulfur. Unlike the Newtonian behaviour of silicate magmas,
molten sulfur has anomalies in the heat capacity (a A-like transistion at 432 K) and in the
viscosity (a maximum at 460 K) due to a polymerization reaction. Numerical modelling
of a pure liquid sulfur supply region at depth in a porous crust shows that the fluid
supply rate from such a magma reservoir is about seven orders of magnitude less than
the observed mass and heat fluxes at the surface of Io. This requires accumulation of
magma in a reservoir prior to eruption at the surface, but the accumulation time on the
order of tens of thousands of years is much longer than would be consistent with the
level of volcanic activity observed on Io. Low sulfur magma supply rates suggest that
sulfur is not the dominant resurfacing material for the satellite. This is consistent with
calculations performed for the viscous relaxation of topography on Io. Surface features
of a largely sulfur crust would disappear within months because of material weakness.
Significant topographic highs and steep slopes on Io provide evidence for a crust with
stronger mechanical properties. Sulfur convection in the crust can still provide a large
fraction of the global heat flow, within certain conditions on the permeability. Previous
estimates of resurfacing rates have equated the cooling of erupted material to the entire
global energy budget. Significant convective transfer of heat by liquid sulfur may call for
a downward revision of resurfacing rates. === Science, Faculty of === Earth, Ocean and Atmospheric Sciences, Department of === Graduate
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