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[46.09] Preliminary Analysis of the Rheological Properties of a Probable Cryovolcanic Flow on Titan, by Radarclinometric Analysis of Cassini RADAR Data

K L Mitchell, R M Lopes (Jet Propulsion Laboratory), R L Kirk (USGS Flagstaff), Cassini Radar Team

Theoretical studies predict that Titan should be cryovolcanically active, erupting mixtures of water, ammonia and possibly methanol, which exhibit behaviour very much like terrestrial silicate lavas [1]. This is supported by interpretations of cryovolcanic landforms in Cassini radar imagery, acquired during the 26/11/2004 fly-by, including a circular dome and several flows of varying length and thickness [2].

One flow, consisting of two sequential lobes each ~40 km in length, emanates from a bright-rimmed circular feature (41^o W, 47^o N) interpreted as a caldera. It exhibits an unusually bright near-edge and dark far-edge across the flow, and appears to be relatively photometrically uniform, so is a prime candidate for morphometric analysis using a prototype radarclinometric method. Our preliminary findings suggest flow thickness of ~200-300 m, with maximum cross-flow slopes of ~7^o.

Assuming Bingham-like behaviour [3], we estimate effective yield strengths of the order of 10⁴ - 10⁴ Pa. Given a high degree of correlation between yield strength and viscosity [1,3], as observed for silicate lavas, we infer viscosities in excess of 10⁵ Pa s, albeit with considerable uncertainty; c.f. [1] who found viscosities of up to ~10¹ Pa s for ammonia-water slurries and ~10⁴ Pa s for ammonia-water-methanol slurries, as well as terrestrial basalts (200 - 2.3x10⁵ Pa s) and andesites (10⁵ - 10⁹ Pa s).

In conclusion, we tentatively suggest that this flow exhibits rheological properties inconsistent with ammonia-water slurries, and is more consistent with ammonia-water-methanol slurries. The effects of supercooling and more exotic compositions should also be considered. Further investigations are required to validate the silicate lava analogy, particularly the yield strength to viscosity correlation.

This work was supported by an NRC Research Associateship and the Cassini project.

[1] Kargel et al. (1991) Icarus 89:93-112. [2] Elachi et al. (2005) Science 308:970-974. [3] Pinkerton & Wilson (1994) Bull. Volcanol. 56:108-120.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.