An excellent summary article is:

Spencer, J.R., and Schneider, N.M., 1996, Io on the eve of the Galileo mission: Annu. Rev. Earth Planet. Sci, v. 24, p. 125-190.

Other useful references:

Anderson, J.D., W.L. Sjogren, and G. Schubert, 1996, Galileo gravity results and the internal structure of Io: Science 272, p. 709-712.

Beatty J. K., O'Leary B., and Chaikin A., eds.,1990, The New Solar System. Sky Publishing Corporation, Cambridge, Massachusetts; Cambridge University Press, New York. 326 pp.

Blaney, D.L., and others, 1997, Io's thermal anomalies: Clues to their origin from comparison of ground-based observations between 1 and 20 mm, in, Special Section: in Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2459-2462.

Carlson, R.W., and others, 1997, The distribution of sulfur dioxide and other infrared absorbers on the surface of Io, in, Special Section: Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2479-2483.

Carr, M.H., Masursky, H., Strom, R.G., and Terrile, R.J., 1979, Volcanic features of Io: Nature, v. 280, p. 729-733

Carr, M.H., 1986, Silicate volcanism on Io: Jour. geophysical res., v. 91, p. 3521-3532.

Clow, G.D., and M.H. Carr, 1980, Stability of sulfur slopes on Io: Icarus 44, p. 268-279.

Crumpler, L.S., 1983, Io: Models of volcanism and interior structure. PhD Dissertation, University of Arizona.

Davies, A.G., and others, 1997, Temperature and area constraints of the South Volund Volcano on Io from NIMS and SSI instruments during the Galileo G1orbit in, Special Section: Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2447-2450.

Fanale, F.P., Brown, R.H., Cruikshank, D.P., and Clark, R.N., 1979, Significance of absorption features on Io's IR reflectance spectrum: Nature, v. 280, p. 761-763.

Fink, J.H., Park, S.O., and Greeley, R., 1983, Cooling and deformation of sulfur flows: Icarus, v. 56, p. 38-50.

Francis, P., 1994, Volcanoes a planetary perspective: Oxford University Press, New York, 443 p.

Greeley, R., and Fink, J., 1984, Sulphur volcanoes on Io?: Astronomy Express, v. 1, p. 25-31.

Greeley, R., Theilig, E., and Christensen, P., 1984, The Mauna Loa sulfur flows as an analog to secondary sulfur flows(?): Icarus, v. 60, p. 189-199.

Greeley, R., P.D. Spudis, and J.E. Guest, 1988, Geologic Map of the Ra Patera Area of Io, U.S. Geological Survey, 1:2M, Map I-1949.

Hanal, R., and others, 1979, Infrared observations of the Jovian system from Voyager 1: Science, v. 204, p. 972-976.

Howell, R.R., D.P. Cruikshank, and F.P. Fanale, 1984, Sulfur dioxide on Io: Spatial distribution and physical state: Icarus, v. 57, p. 83-92.

Ingersoll, A.P., 1989, Io Meterology: How Atmospheric Pressure is Controlled Locally by Volcanoes and Surface Frosts: Icarus, Vol. 81, p. 298.

Johnson, T.V. and others, 1988, Io: Evidence for silicate volcanism in 1986: Science, v. 242, p. 1280-1283.

Keszthelyi, L. and McEwen, A., 1997, Thermal models for basaltic volcanism on Io, in, Special Section: Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2463-2466.

Lewis, J.S., 1982, Io: Geochemistry of sulfur. Icarus 50, p. 103-114.

Lopes-Gautier, R., and others, 1997, Hot spots on Io: Initial results from Galileo's near infrared mapping spectrometer, in, Special Section: Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2439-2442.

Masursky, H., Schaber, G.G., Soderblom, L.A., and Strom, R.G., 1979, Preliminary geological mapping of Io: Nature, v. 280, p. 725-729.

McEwen, A.S., 1988, Global color and albedo variations on Io: Icarus, v. 73, p. 385-426.

McEwen A. and others, 1997, High-temperature hot spots on Io as seen by the Galileo solid state imaging (SSI) experiment in, Special Section: Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2443-2446.

McEwen A. and others, 1989, Dynamic geophysics of Io. In Time-Variable Phenomenon in the Jovian System, pp. 11-46, NASA Special Publication 494.

McEwen A.S., Lunine, J.I., and Carr, M.H., 1989, Dynamic geophysics of Io, NASA Special Publication 494, p. 11-46.

Moons and Rings, 1991, Voyage Through the Universe series. Time-Life Books, Alexandria, Virginia. 144 pp.

Morabito, L.A., Synnot, S.P., Kupferman, P.N., and Collins, S.A., 1979, Discovery of currently active extraterrestrial volcanism: Science, v. 204, p. 972.

Morrison D., ed., 1982, Satellites of Jupiter. University of Arizona Press, Tucson. 972 pp.

Nash D. et al., 1986, Io. In Satellites (J. Burns and M. Matthews, eds.), p. 629, University of Arizona Press, Tucson.

Nelson, R.M., Peiri, D.C., Nash, D., and Baloga, S.M., 1982, Reflection spectrum of liquid sulphur and its implications for Io: Rep. Planet. Geol. Prog. - 1982, NASA TM-85127, 12-15.

Peale, S.J., Cassen, P. and Reynolds, R.T., 1979, melting of Io by tidal dissipation: Science, v. 203, p. 892-894.

Rothery D., 1992, Satellites of the Outer Planets. Clarendon Press, Oxford. 208 pp.

Schaber, G.G., D.H. Scott, and R. Greeley, 1989, Geologic Map of the Ruwa Patera Quadrangle of Io, U.S. Geological Survey, Quadrangle Ji2, 1:5M, Map I-1980.

Schaber, G.G., 1980, The surface of Io: geologic units, morphology and tectonics: Icarus, v. 43, p. 302-333.

Schaber, G.G., 1982, The geology of Io: in Satellites of Jupiter. D. Morrison (ed.), p. 556-597, University of Arizona Press, Tucson.

Schenk P. et al., 1997, Geology and topography of Ra Patera, Io, in the Voyager era: Prelude to eruption. Geophys. Res. Lett., 24, 2467-2470.

Smith, B.A., Shoemaker, E.M., Kieffer, S.W., and Cook, F.A., 1979, The role in SO2 volcanism on Io: Nature, v. 280, p. 738-743.

Spencer, J.R., and others, 1997, Volcanic resurfacing on Io: Post-repair HST images, in press, Icarus.

Spencer, J.R., and others, 1997, A history of high-temperature Io volcanism: February 1995 to May 1997, in, Special Section: Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2451-2454.

Spencer, J.R., and others, 1997, The Pele plume (Io): Observations with the Hubble Space Telescope, in, Special Section: Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2471-2474.

Spencer J. and Schneider N., 1996, Io on the eve of the Galileo mission. Annual Reviews of Earth and Planetary Science, 24, 125.

Stansberry, J.A., and others, 1997, Violent silicate volcanism on Io in 1996, in, Special Section: Io Volcanism in the Galileo Era: Geophysical Research Letters, v. 24, no. 20, p. 2455-2458.

Strom, R.G., and others, 1981, Volcanic eruptions on Io: Jour. geophysical res., v. 86, p. 8593-8620.

Strom R.G., and others, 1979, Volcanic eruption plumes on Io: Nature: v. 280, p. 733-736.

Taylor, S.R., 1992, Solar System Evolution: A new perspective: New York, Cambridge University Press.

Watanabe, T., 1940, Eruptions of molten sulfur from the Siretoko-Iosan volcano, Hokkaido, Japan: Japan. J. Geol. Geogr. V. 17, p. 289-310.

Wilson, L., and Head, J., 1983, A comparison of volcanic processes on Earth, Moon, Mars, Io, and Venus: Nature, v. 302, p. 663-669.