Mathematics – Logic
Scientific paper
Nov 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993jgr....9820891c&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 98, no. E11, p. 20,891-20,902
Mathematics
Logic
23
Channel Flow, Ejecta, Impact Damage, Morphology, Planetary Craters, Planetary Geology, Venus (Planet), Venus Surface, Flow Distribution, Magellan Spacecraft (Nasa), Mathematical Models, Melting, Satellite Imagery, Topography
Scientific paper
Many of the 932 impact craters discovered by the Magellan spacecraft at Venus are associated with lobate flows that originate at or near the crater rim. They extend for several to several hundred kilometers from the crater, and they commonly have a strong radar backscatter. A morphologic study of all identifiable crater outflows on Venus has revealed that many individual flows each consist of two areas, defined by distinct morphologic features. These two areas appear to represent two stages of deposition for each flow. The part of the flow that is generally deposited closest to the crater tends to be on the drownage side of the crater, flows in the downrange direction, and it is interpreted to be a late-stage ejecta. Dendritic channels, present in many proximal flows, appear to have drained liquid from the proximal part downhill direction, and they debouch to feed the outer part of the flows. The distal part flows downhill, fills small grabens, and is ponded by ridges, behavior that mimics that of volcanic lava flows. The meandering and dendritic channels and the relation of the distal flows to topography strongly suggest that the distal portion is the result of coalescence and slow drainage of impact melt from the proximal portion. Impact melt forms a lining to the transient crater and mixes turbulently with solid clasts, and part of the mixture may be ejected to form the proximal part of the flow during the excavation stage of crater development. A statistical study of the Venusian craters has revealed that, in general, large craters produced by impacts with relatively low incidence angles to the surface are more likely to produce flows than small craters produced by higher-angle impacts. Numerical models have predicted that large volumes of impact melt would be produced on Venus than on the cooler terrestrial bodies due to high atmospheric and target temperatures, perhaps 3 times the volume produced on the Moon for a given crater diameter.
Chadwick David J.
Schaber Gerald G.
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