On geologic processes in the lowland regions of Venus

Rolling lowland plains comprise ∼80% of Venus' surface, thus developing a geologic understanding of processes in these regions are critical for understanding Venus' geologic evolution. Here, I use NASA Magellan Synthetic Aperture Radar and altimetry radar data to elucidate geologic processes that operate within Venusian lowlands.; Chapter 1 presents results of 1:5,000,000 scale geologic mapping of Llorona Planitia (Greenaway quadrangle; 0°-25° N, 120°-150° E), a region that includes a representative portion of the lowlands. Geologic mapping of this region provides insights into volcanic and tectonic processes that shaped the Venusian lowlands. Map relations illustrate that small shield edifices, which reflect local point-source volcanism, resurfaced most of the study area. Coronae, circular to quasi-circular volcano-tectonic structures, appear to have played a minor role in resurfacing at this location.; Chapter 2 is a qualitative study of Venusian channels, sinuous features on Venus' surface that transported, and were carved by, fluids. I constructed geologic maps of channels in three geographically separate regions with the express goal of delineating the operative processes involved in Venusian channel formation. Channels in each region dissect pre-existing topographic highs with no deflection in the channel course by surface topography, relationships difficult to justify with the widely held view that Venusian channels formed by surface processes. I propose that channels evolved through subsurface fluid flow that involved local stoping and erosion of overlying material.; In Chapter 3, I develop a quantitative approach to address Venusian channel formation. Specifically, I build on the work presented in Chapter 2 and develop a mathematical model that singularly addresses the role of thermal erosion in channel formation. In the model, I use the control volume method to track the changes in the channel width and magma velocity and temperature at a fixed control volume. I conclude that thermal erosion could play a significant role in Venusian channel formation; the heat transfer coefficient will govern the magnitude of thermal erosion. Further, modeling suggests that thermal erosion can be driven by lava as common as basalt. Finally, I postulate that the widths of Venusian channels may be controlled by heat loss from the conduit top.*; *This dissertation is a compound document (contains both a paper copy and a CD as part of the dissertation). The CD requires the following system requirements: Adobe Acrobat; Microsoft Office.