Journal article Open Access

Silicate volcanism on Io

Carr, Michael H.

Io is currently emitting 1–1.5 W m−2 of tidal energy as a result of its volcanic activity. If the lithosphere is more than 20 km thick, as appears probable from the surface relief, only a fraction of the tidal energy can be dissipated within the lithosphere, otherwise it will become thinner. The rest of the tidal energy must be dissipated below the lithosphere. Io is likely to be highly differentiated as a result of the volcanic activity, with a low melting temperature fraction, such as basalt, near the surface and a high melting temperature fraction, such as peridotite, at depth. If solidus temperatures are reached at depths shallower than the thickness of the basalt layer, a partial melt zone will separate an all‐basalt lithosphere above from a peridotite mantle below, and part of the tidal energy will be dissipated by viscous deformation within the melt zone. Most of the energy dissipated below the lithosphere will be transported upward through the lithosphere as silicate magma, which is generated in quantities sufficient to resurface the satellite at a rate of a few tenths of a centimeter a year, depending on the lithosphere thickness. Many of the characteristics of the Ionian surface have been explained in terms of sulfur volcanism. However, most of the features observed can be as readily explained by silicate volcanism, and silicates are more consistent with the apparent strength of the surface as implied by the relief. Simulations of basaltic eruptions indicate that the surface temperatures that would result from basaltic eruptions are similar to those measured by the Voyager infrared interferometer spectrometer experiment. The high rates of emission by the Ionian hot spots imply eruption rates that are high compared with typical terrestrial eruptions. An eruption rate of 4000 m3 s−1 may be required to explain Loki which is currently emitting 1013 W. Although the near‐surface materials are mainly silicate, they may contain several percent of volatile components rich in S, Na, and K. Remobilization of these components by the ongoing silicate eruptions causes the plumes, provides material to the torus, and gives the satellite its characteristic reflectivity.
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