LARGE-SCALE SPATIAL PATTERNS IN TOPOGRAPHY AT ALPHA-REGIO, VENUS

Hypsometric topographic analysis of Magellan altimetry data at Alpha R egio results in a multimodal distribution. Planimetric display of the spatial distribution for altitudes close to each mode reveals large-sc ale ring-like and crescentic patterns. The latter result from the inte rsection of horizontal altitude ranges with sloping patterns that are quasicircular in shape. The spatial patterns of topographic features n ear Alpha Regio have the following attributes: (1) quasicircular shape s of individual elements; (2) a hierarchy of distinctive sizes for tho se elements, with diameters of various elements at approximately 2800, 1500, 500-700, and 200 km; and (3) a large-scale arrangement or patte rn in which the 1500-km highland plateau of Alpha Regio is surrounded by a ring of 500-km structures, all of which constitute a 2800-km mega structure. We hypothesize that the intricate patterns of hierarchical scaling for large-scale spatial elements of Venusian topography result from corresponding complexity in Venusian mantle convection.