![]() ![]() ![]() The SAR images are left-looking Cycle 1 from the Magellan mission NNW–SSE-trending black bands are gaps in the radar image data. Types of stream drainage on Earth are after Howard (1967)³⁵ and Bridge and Demicco (2008)³⁶. Each row features a Magellan SAR image (left) on which an interpreted valley pattern is drawn based on the volcanic flooding (centre) and which is matched to terrestrial stream drainage patterns (right). Shows tesserae regions that are partially flooded by lava flows and our interpretation of the resultant patterns in terms of stream drainage patterns. Valley patterns revealed by lava flooding and our fluvial interpretation Noteworthy are the white dashed lines in e that correspond to prominent lineament sets that may reflect inward dipping strata on both flanks of the inferred syncline. The tessera is orange and the younger mafic lava flows are light yellow, and the smooth yellowish-white band is the missing data. Vertical exaggeration is 20× and the viewing elevation angle is about 20°. e Elevated oblique view (looking north) generated by draping the SAR image onto Magellan altimetry topography using the software ArcScene. T = tesserae and L = younger mafic lava flows. ![]() b–d End-member generalized alternative geological interpretations for cross-section A–A’ of which only the third (d) fits the observations: b a purely tectonic interpretation whereby these landforms are a central syncline and bordering anticlines c a purely fluvial erosional interpretation, or d initial tectonic activity (synclinal folding) followed by fluvial erosion. Edge of main flooding (red line) on left side extrapolated from the SAR image on both sides of the data gap. Red portion of topographic profile corresponds to the portion flooded and embayed by plains lavas. Dotted portion of brown line extrapolates across a topographic data artefact (appearing as a topographic ‘hole’) in the dataset. ![]() The topographic relief between the valley (covered by lava flows) and bordering tesserae hills is about 100 m (along profile line A–A’). White band marks absence of Magellan SAR data, but topographic data are available in this region. This proposed fluvial erosion in tesserae provides support for climate models for a cool, wet climate on early Venus and could be an attractive research theme for future Venus missions.Įvidence for erosion in the southern portion of Salus tesseraĪ Left-looking Cycle 1 Magellan SAR image (central coordinates 4.4°S, 48.2☎) north is up, showing tessera (light grey and lineated) with a re-entrant area that has been flooded by younger plains lavas (featureless dark grey). These observed valley patterns are attributed to primary geology, tectonic deformation, followed by fluvial erosion (and lesser wind erosion). Given poor topographic resolution, we use an indirect technique to recognize valleys, based on the pattern of lava flooding of tesserae margins by adjacent plains volcanism. We observe that the stratigraphically oldest, geologically most complex units, tesserae, exhibit valley patterns morphologically similar to the patterns resulting from fluvial erosion on Earth. However, recent global circulation models suggest the possibility of Earth-like climatic conditions on Venus for much of its earlier history, prior to catastrophic runaway greenhouse warming. Fluvial erosion is usually assumed to be absent on Venus, precluded by a high surface temperature of ~450 ☌ and supported by extensive uneroded volcanic flows. ![]()
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