Origin of Mountains on Io by Thrust Faulting and Large-Scale Mass Movements

A. McEwen et al., in Time-Variable Phenomena in the Jovian System (NASA Spec. Publ. 494, NASA, Washington, DC, 1989), pp. 3–46;

Veeder G., et al., J. Geophys. Res. 99, 17095 (1994).

G. Schaber, in Satellites of Jupiter, D. Morrison, Ed. (Univ. of Arizona Press, Tucson, AZ, 1982), pp. 556–597.

Schenk P., et al., Geophys. Res. Lett. 24, 2467 (1997).

M. Carr, Geol. Soc. Am. Abstr. Programs 29, A-311 (1997).

This software was developed in 1995–96 at the Lunar and Planetary Institute by P. Schenk and B. Fessler for use with Voyager images and employs a scene-recognition algorithm to locate features in each image and determine parallax (3).

McCauley J., et al., Nature 280, 736 (1979);

Moore J. M., et al., Icarus 122, 63 (1996).

H. J. Moore, U.S. Geol. Surv. Misc. Investig. Map I-1851 (1987).

P. W. Francis and G. L. Wells, Bull. Volcanol. 50, 258 (1988).

Shreve R. L., Science 154, 1639 (1966).

P. J. Shaller, thesis, California Institute of Technology, Pasadena (1991); M. H. Bulmer, thesis, University of London (1994).

J. E. Guest, in Geology and Physics of the Moon, G. Fielder, Ed. (Elsevier, Amsterdam, 1971), pp. 93–103.

P. J. Shaller, Can. Geotech. J. 28, 584 (1991).

A. Heim, Bergstruz und Menschenleben (Fretz und Wasmuth, Zurich, 1932), p. 218.

Lucchitta B., Geol. Soc. Am. Bull. 89, 1601 (1978).

Yarnold J. C., ibid. 105, 345 (1993).

L. Muller, Rock Mech. Eng. Geol. 6, 1 (1968).

B. Voight and W. Pariseau, in Geotechnical Engineering, B. Voight, Ed. (Elsevier, Amsterdam, 1978), pp. 1–67.

Lopes R., et al., J. Geophys. Res. 87, 9917 (1982);

; R. Lopes et al., Moon Planets 22, 221 (1980);

Francis P. W., Wadge G., J. Geophys. Res. 88, 8333 (1983);

; M. Bulmer and P. McGovern, Lunar Planet. Sci., in press.

R. Dingle, J. Geol. Soc. London 134, 293 (1977); C. Summerhayes et al., Mar. Geol.31, 265 (1979).

See P. Schenk and M. Bulmer [Lunar Planet Sci.XXVIII, 1247 (1997)] and M. Bulmer (in preparation), and references therein.

The average friction coefficient is given by the tangent of the slope connecting the pre- and postevent centers of gravity of a failed mass (30). Because it is not possible to determine the pre- and postevent centers of gravity for masses on Io or most other planets, we use the tangent of the slope angle of the line connecting the top of the scarp to the toe of the apron (13) to derive the ratio H:L. The value derived using this method approximates the center of gravity gradient for those slope failures whose center of gravity lies near the toe (10), which may be the case for Euboea. Taking these caveats into consideration, we use H:L as an estimate of the coefficient of friction.

M. H. Bulmer and J. E. Guest, in Volcano Instability on the Earth and Other Planets, W. J. McGuire, A. P. Jones, J. Neuberg, Eds. (Geological Society of London, London, 1996), p. 349.

At 16 km height, Boosaule Montes (10°S, 270°W) is the highest mountain identified to date on Io. The automated stereogrammetry (5) measurement we report has been confirmed by manual measurement of parallax in the Voyager images.

Previous estimates that the crust of Io is ∼30 km thick (31) assumed that mountain heights are due to isostatic buoyancy of material that is lower in density than the surrounding crust. Our interpretation of the formation of Euboea Montes suggests that mountains may have the same density as the surrounding crust, indicating that these crustal thickness estimates are not generally relevant to Io.

R. Allmendinger, in Geology of North America—An Overview, vol. G-3 of Geology of North America, B. Burchfiel, P. Lipman, M. Zoback, Eds. (Geological Society of America, Boulder, CO, 1992), pp. 583–608; D. Miller, T. Nilsen, W. Bilodeau, ibid., pp. 205–260.

Jordan T., Allmendinger R., Am. J. Sci. 286, 737 (1986).

Smithson S., et al., J. Geophys. Res. 84, 5955 (1979).

On Io, it is not known whether such faults penetrate the crust or the lithosphere.

Lopes-Gautier R., et al., Geophys. Res. Lett. 24, 2439 (1997);

; M. Carr, paper presented at the Lowell Observatory during the Galileo Era Conference, Flagstaff, AZ, 22 to 24 September 1997.

Cruden D., Geol. Soc. Am. Bull. 91, 63 (1980).

D. Nash et al., in Satellites, J. Burns and M. Matthews, Eds. (Univ. of Arizona Press, Tucson, AZ, 1986), pp. 629–688.

This report is Lunar and Planetary Contribution No. 940. This work was done while M.H.B. was a Garber Fellow at the National Air and Space Museum. We are grateful to J. Moore, W. McKinnon, and an anonymous reviewer for comments.