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W Schwarz, R Greeley, J Fink (Ariz. State Univ.), Galileo SSI Imaging Team
The first and most prominent europan domes were imaged during the sixth orbit of the Galileo spacecraft, and they have been found subsequently in many other areas of Europa. Most domes range in diameter from 3 to 6 km, have heights of 60 to 100 m, and have a `moat' or dark halo surrounding them. They usually are axisymmetric in planform and have a `spiny' surface texture. This morphology is similar to that of some terrestrial lava domes. Laboratory simulations and field work on terrestrial lava domes were used to develop models that relate lava flow morphology to rheology and effusion rate [1,2]. These models have been modified for a europan environment, and several estimates of the physical properties of the erupted `cryolava' are used, assuming water ice. The morphology of europan domes resembles the types that result from the extrusion of a bingham-plastic material. The aspect ratios of 10 europan domes, determined by photoclinometry, were used to estimate the yield strength of the potential `cryolava'. The resulting yield strength of 3.3 kPa combined with observations of the morphology types seen in Galileo images was then used to constrain the effusion rates of the `cryolava' that formed the domes. Estimated effusion rates between 0.01 m3/s and 1.0 m3/s were obtained, assuming pure water ice. These values can place constraints on the ice properties and composition of cryomagmas as well as the thickness of the lithosphere.
References: [1] Fink and Griffiths, 1990. J. Fluid Mechanics, 221, pp. 485-509.; [2] Fink and Griffiths, 1998, J. Geophysical Research, 103, B1, pp.527-545.
The author(s) of this abstract have provided an email address for comments about the abstract: wschwarz@asu.edu