NASA NTRS1992
After a preliminary assessment of venusian channels, it now seems to be clear that the channels have distinctive classes, which imply a wide range of formation parameters and formation mechanisms. They include outflow channels mainly formed by mechanical erosion from very high discharge flow, and canali-type channels requiring either constructional process or mechanical erosion by rather exotic low-viscosity lava such as carbonatite or sulfur. Here we focus on venusian sinuous rilles. Venusian sinuous rilles are generally simple, and originate from a collapsed source. They are shallow and narrow downstream. The venusian sinuous rilles are distinct from canali-type channels, which exhibit almost constant morphologies throughout their entire length, and from outflow channels, which are characterized by wide anastomosing reaches. The lunar sinuous rilles could have been formed initially as constructional channels. However, incision was caused by the long flow duration and high temperatures of eruption, along with relatively large discharge rates, possibly assisted by a low viscosity of the channel-forming lava. Channel narrowing and levee formation suggest relatively fast cooling. The venusian channels could have had a similar sequence of formation including rapid cooling. Assuming the substrate is typical tholeiitic lava, the flowing lavas' temperatures have to be higher than the melting temperature of the substrate. The flow should have a low viscosity to cause turbulence and keep a high Reynolds number to sustain efficient thermal erosion. Determining eruption conditions also provide insights to estimate lava composition. Assuming a channel is formed mostly by thermal erosion, the channel's length and longitudinal profile are functions of lava properties. The depth profiles of the channel are measured by radar foreshortening methods and stereo images. Eruption conditions of channel forming lava can be estimated by the methods developed by Hulme.