DPS 2001 meeting, November 2001
Session 24. Io, Tori, and Satellite Atmospheres
Oral, Chairs: I. de Pater, W. Smythe, Wednesday, November 28, 2001, 5:00-6:40pm, Regency E

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[24.03] The Rheology and Emplacement of the Lava Flows on Io

R. R. Wilson, P. M. Schenk (LPI), A. G. Davies (JPL)

Thermal measurements on Io have indicated high temperature lava eruptions consistent with low silica lavas mafic or ultramafic in composition. Stereo derived topographic studies of the shield-like volcanoes on Io may lead to a better understanding of the rheology of Ionian lavas. Most Ionian volcanoes have little relief with the greatest relief of less than 2 km and slopes ranging from 0.2 to 0.6.

We have adopted Jeffrey's equation to estimate lava viscosities and assumed a Bingham's rheology for constraining the yield strength of the Ionian lavas. Flow thickness is unknown but limited shadow measurements indicate an upper limit of ~20 m. Flow velocities may be as high as 10 m/s (but not less than 1 cm/s). William's values for komatiite density were also applied in estimating both yield strength and viscosity of Io's lavas. Estimated lava viscosities range from 101 to 103 Pa s but could be as high as 106 Pa s for assumed komatiite and basalt compositions. Yield strength was calculated for both types of lavas and upper and lower bounds for both were very similar. Maximum yield strengths for Ionian lavas may be 103 Pa with a lower bound of 102 Pa.

Low slopes and heights estimated for volcanoes on Io are also suggestive of very-low silica high-temperature eruptions. Our measured low slopes coupled with long run out distances of several hundred kilometers are at least consistent with low viscosities and yield strengths for the erupting lavas on Io, supporting arguments for mafic or ultramafic compositions such as basalt or komatiite for Ionian lavas.

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