Fractal properties of outflows from Venusian impact craters

This article presents fractal analyses of 28 outflow margins from 18 Venusian impact craters. The fractal dimensions of the second parts of R-plots of the outflow outlines were measured by a three-step method. The fractality values for the same outflow measured from images which have only a small difference in resolution are very similar, while large differences in image resolution may result in differences in fractality, possibly due to the fact that we are actually studying geological processes on different scales. The outflows were classified into three general categories: single outflows, multiple outflows and outflow fields. Three conclusions were drawn on the relations between fractality and crater diameter, which may be related to the greater effects caused by the immediate local environment on the outflows from small craters than on those from larger craters. Investigation of the relations between the regional topography and fractality indicates that there are substantially less effects on outflows originating from large craters than on those from small craters. The smooth bending in the R-plot and the higher D-value for the multiple outflows could result from the mixing of various fractal or non-fractal units. When comparing our results with the fractality of terrestrial lava flows, outflows from craters of diameter greater than 50 km seem to resemble aa-type lava flows in their fractal dimensions and outflows from craters of diameter below 50 km tend to be more pahoehoe-like. This preliminary result is based on 28 outflows, however, and the pattern should be investigated more carefully by further more extensive work.