Regional slope values for earth and Venus are calculated for each 3° × 3° region of topography, and the global characteristics of these magnitudes are examined and compared. The effects on terrestrial regional slope due to ocean loading are treated by approximating the component of seafloor depth due to the weight of the overlying water column and removing this component from the ocean topography. Although regional slopes on Venus and earth span the same range, 0.0°–2.4° (±0.07°), the slope frequency distributions for the two planets differ significantly. The most abundant regional slope values for the terrestrial cases (earth and unloaded earth) are 0.0° and reflect the presence of vast plains associated with the continental interiors and ocean abyssal plains. In contrast, Venus exhibits a peak in slope frequency at approximately 0.09°, perhaps indicating less effective planation processes in the absence of a hydrosphere. Surfaces with regional slope values of 0.07°–0.24° are substantially more common on Venus than on earth. Slopes in this range are associated with discrete features in the lowland and upland rolling plains provinces of Venus and may be indicative of a geologic process that is not commonly observed on earth. Only 14±1% of all Venus surfaces have regional slopes above 0.24°, compared to 26±1% for earth. When mean regional slope is calculated as a function of elevation, a distinctive positive correlation is expressed on Venus. In contrast, the terrestrial cases exhibit a complex relationship marked by four modes related to the presence on earth of an active hydrosphere-driven weathering regime, a distinctive crustal dichotomy, and plate tectonics. The distinctions in the regional slope characteristics between Venus and earth point to a simpler, less diversified geology on Venus.
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