page_title: Surface features of Venus
section_title: Channels/valles
hierarchical_section_title: Surface features of Venus / Channels/valles
caption_attribution_description: PIA00245: Venus - 600 Kilometer Segment of Longest Channel on Venus This compressed resolution radar mosaic from Magellan at 49 degrees north latitude, 165 degrees east longitude with dimensions of 460 by 460 kilometers (285 by 285 miles), shows a 600 kilometers (360 mile) segment of the longest channel discovered on Venus to date. The channel is approximately 1.8 kilometers (1.1 miles) wide. At more than 7,000 kilometers (4,200 miles) long, it is several hundred kilometers longer than the Nile River, Earth's longest river, thus making it the longest known channel in the solar system. Both ends of the channel are obscured, however, so its original length is unknown. The channel was initially discovered by the Soviet Venera 15-16 orbiters which, in spite of their one kilometer resolution, detected more than 1,000 kilometers (620 miles) of the channel. These channel-like features are common on the plains of Venus. In some places they appear to have been formed by lava which may have melted or thermally eroded a path over the plains' surface. Most are 1 to 3 kilometers (0.6 to 2 miles) wide. They resemble terrestrial meandering rivers in some aspects, with meanders, cutoff bows and abandoned channel segments. However, Venus channels are not as tightly sinuous as terrestrial rivers. Most are partly buried by younger lava plains, making their sources difficult to identify. A few have vast radar-dark plains units associated with them, suggesting large flow volumes. These channels, with large deposits appear to be older than other channel types, as they are crossed by fractures and wrinkle ridges, and are often buried by other volcanic materials. In addition, they appear to run both upslope and downslope, suggesting that the plains were warped by regional tectonism after channel formation. Resolution of the Magellan data is about 120 meters (400 feet). The white margins and arrows have been added to the NASA image.
context_page_description: The surface of Venus is dominated by geologic features that include volcanoes, large impact craters, and aeolian erosion and sedimentation landforms. Venus has a topography reflecting its single, strong crustal plate, with a unimodal elevation distribution that preserves geologic structures for long periods of time. Studies of the Venusian surface are based on imaging, radar, and altimetry data collected from several exploratory space probes, particularly Magellan, since 1961. Despite its similarities to Earth in size, mass, density, and possibly composition, Venus has a unique geology that is unlike Earth's. Although much older than Earth's, the surface of Venus is relatively young compared to other terrestrial planets, possibly due to a global-scale resurfacing event that buried much of the previous rock record. Venus is believed to have approximately the same bulk elemental composition as Earth, due to the physical similarities, but the exact composition is unknown. The surface conditions on Venus are more extreme than on Earth, with temperatures ranging from 453 to 473 °C and pressures of 95 bar.
context_section_description: The surface of Venus contains over 200 channel systems and named valles, that resemble terrestrial rivers. These channels vary in length and width and are commonly found in planar regions of the planet. Channel length and width ranges from the minimum resolution of Magellan imaging to over 6800 km long (Baltis Vallis) and up to 30 km wide. Their global distribution is not uniform, and tend to concentrate around the equatorial region, near volcanic structures. Venusian valles also show characteristics of flows, such as levees on the margins and downstream narrowing and shallowing. Channels also do not contain tributaries, despite their large scale. However, because of the high surface temperature of Venus, liquid water is unstable, making their comparison with terrestrial rivers difficult.  These features are similar to lava flows on other terrestrial planets, which has led to the conclusion that these valleys likely formed from volcanic flows. This is also suggested by the evidence of cooled lava flows filling the valles. Channels  likely formed in very short timescales (1–100 years), indicating very fast movement and erosion of lavas. Venusian channels are classified by morphology and include three types: simple, complex, and compound.
  Simple channels are single channel valleys with little to no branching or anastomosing. Types of simple channels observed on Venus include sinuous rilles, simple channels with flow margins, and canali. Sinuous rilles are like those seen on the Moon; narrow erosive channels that originate from regions of volcanic collapse, such as coronae. Simple channels with flow margin are located in obvious flow fields, have an undefined source and end, and are believed to feed into large flows from surrounding volcanics. Canali, like the Baltis Vallis, are long flows with constant width and depth that may contain abandoned channels, bends, and levees, indicating they are sourced from large amounts of thick lavas.
  Complex channels are channels that can be braided, anastomosing, or in distributary patterns. They commonly form on lava flow deposits, but also occur elsewhere. Complex channels without flow margins may form part of a larger flow system, and form as channels of lava flows erode into the crust. Complex channels with flow margins appear as non-erosional, and their individual channels are separated by islands of crust of differing radar qualities.
  Compound channels show simple and complex channel structures. These channels usually begin as simple channels and bifurcate and meander as flow energy decreases on its distal reaches.
caption: Radar mosaic from Magellan showing a 600-km-long segment of Baltis Vallis, a channel on Venus that is longer than the Nile
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