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Surface features of Venus
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 (over 90% of the surface lies within an elevation of -1.0 and 2.5 km) 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 (see Venus Exploration). 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 (<500 million years old), 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. Venus lacks water, which makes crustal rock stronger and helps preserve surface features. The features observed provide evidence for the geological processes at work. Twenty feature types have been categorized thus far. These classes include local features, such as craters, coronae, and undae, as well as regional-scale features, such as planitiae, plana, and tesserae.
==Plains==
Plains are large areas of relatively flat topography on Venus that form at varying elevations. Plains with elevations within 1–3 km of the datum are referred to as lowland plans, or ''planitiae'', and those above are named highland plains, or ''plana''.〔 Plains cover 80% of the Venusian surface, and, unlike those seen on other silicate planets, are heavily faulted or fractured throughout. Structurally, these plains contain features such as wrinkle ridges, grabens (''fossa'' and ''linea''), fractures, scarps (''rupes''), troughs, hills (''collis''), and dikes in both local and region scales. Plains often contain visible flow patterns, indicating a source from volcanic lava flows. The more pronounced lave flow fields are named ''fluctūs''. The presence of surface flow patterns, in conjunction with crosscutting valleys, has given rise to the hypothesis that these plains likely formed by global lava flows over a short timescale and were subsequently exposed to compressional and extensional stresses. Structurally, plains are often deformed in belts of ridges (''dorsa'') or fractures (''lineae'') of various orientation and morphology.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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