ATTRIBUTES OF STREAMLINED ISLANDS IN VENUSIAN CHANNELS: IMPLICATIONS FOR THEIR ORIGIN AND USE AS FLOW DIRECTION INDICATORS

NASA's Magellan mission in the early 1990s provided a near-global dataset of high-resolution radar images that revealed a plethora of distinctive landforms. Among these are over 200 channels snaking across the planet's surface. Interestingly, some of these channels contain streamlined features or islands. Here we explore the physical characteristics of streamlined islands in Venusian channels to address two questions: What could explain their origins? And might they serve as markers for reconstructing the direction of material that once flowed through these channels? To address these questions, we utilized Magellan radar images (~75 m/pxl) and altimetry data to examine 15 channels with an obvious origin and terminus. In all cases, the streamlined islands resemble elongated teardrops, with tapered ends pointing downstream and blunt ends facing up channel. Six channels contained a total of 11 streamlined islands whose lengths, widths, shapes, and elevation profiles were measured; several of these features spanned several tens of kilometers in both width and length, with the largest being ~36.5 km long and ~12.4 km wide and the smallest being ~1.7 km long and ~0.6 km wide. Qualitatively, the surfaces of the larger islands appear to be at the same level of the substrate on either side of the channel. Additionally, there seemed to be a correlation between shape and flow direction. In most cases, the elongated tails of the islands pointed downstream while their blunt ends faced upstream. This shape strongly suggests they were sculpted and streamlined by flowing lava or volcanic debris moving through the channels. These streamlined islands likely formed in two ways. The first way, which may be represented by smaller streamlined islands inside a distinct channel may be the result of material left over from waning flow; these streamlined islands are therefore likely constructional in origin. The second way, which is likely represented by the largest of the islands is that they are the result of material diverging around a stronger or more resistant section of substrate; in this situation, the channel forming material eroded into a substrate, but was then deflected around more resistant bedrock. These findings hint that these enigmatic islands could be used to reconstruct flow directions in channels with non-obvious origins.