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Alba Mons (formerly known as Alba Patera, a term that has since been restricted to the volcano's summit caldera) is an immense, low-lying volcano located in the northern Tharsis region of the planet Mars. It is the largest volcano on Mars in terms of area, with volcanic flow fields that extend for at least from its summit.〔Cattermole, 2001, p. 85.〕 Although the volcano has a span comparable to that of the United States, it reaches an elevation of only at its highest point.〔Carr, 2006, p. 54.〕 This is about one-third the height of Olympus Mons, the tallest volcano on the planet.〔Plescia, J. B. (2004). Morphometric Properties of Martian Volcanoes. ''J. Geophys. Res.,'' 109(E03003), Tbl. 1, .〕 The flanks of Alba Mons have very gentle slopes. The average slope along the volcano's northern (and steepest) flank is 0.5°, which is over five times lower than the slopes on the other large Tharsis volcanoes.〔〔Boyce, 2008, p. 104.〕 In broad profile, Alba Mons resembles a vast but barely raised welt on the planet's surface.〔See Carr, 2006, p. 54, Fig. 3.10 for MOLA profile of Alba Mons compared to Olympus Mons. The difference in relief is striking.〕 It is a unique volcanic structure with no counterpart on Earth or elsewhere on Mars.〔 In addition to its great size and low relief, Alba Mons has a number of other distinguishing features. The central portion of the volcano is surrounded by an incomplete ring of faults (graben) and fractures, called Alba Fossae on the volcano's western flank and Tantalus Fossae on the eastern flank. The volcano also has very long, well preserved lava flows that form a radiating pattern from the volcano's central region. The enormous lengths of some individual flows (>) implies that the lavas were very fluid (low viscosity) and of high volume. Many of the flows have distinctive morphologies, consisting of long, sinuous ridges with discontinuous central lava channels. The low areas between the ridges (particularly along the volcano's northern flank) show a branching pattern of shallow gullies and channels (valley networks) that likely formed by water runoff. Alba Mons has some of the oldest, extensively exposed volcanic deposits in the Tharsis region. Geologic evidence indicates that significant volcanic activity ended much earlier at Alba Mons than at Olympus Mons and the Tharsis Montes volcanoes. Volcanic deposits from Alba Mons range in age from Hesperian to early Amazonian〔Ivanov, M. A.; Head, J.W. (2006), Alba Patera, Mars: Topography, Structure, and Evolution of a Unique Late Hesperian–Early Amazonian Shield Volcano. ''J. Geophys. Res.,'' 111 E09003, .〕 (approximately 3600〔Werner, S.C.; Tanaka, K.L.; Skinner, J.A. (2011). Mars: The Evolutionary History of the Northern Lowlands Based on Crater Counting and Geologic Mapping. ''Planet. Space Sci.,'' in press, .〕 to 3200 million years old). ==Name origin== For years the volcano's formal name was Alba Patera. ''Patera'' (pl. ''paterae'') is Latin for a shallow drinking bowl or saucer. The term was applied to certain ill-defined, scalloped-edged craters that appeared in early spacecraft images to be volcanic (or non-impact) in origin.〔Russell, J.F.; Snyder, C.W.; Kieffer, H.H. (1992). Origin and Use of Martian Nomenclature in ''Mars,'' H.H. Kieffer ''et al.,'' Eds.; University of Arizona Press: Tucson, AZ, p. 1312.〕 In September 2007, the International Astronomical Union (IAU) renamed the volcano Alba Mons (Alba Mountain), reserving the term Alba Patera for the volcano's two central depressions (calderas).〔 Nevertheless, the entire volcano is still commonly called Alba Patera in the planetary science literature.〔A Google Scholar search of the astronomy and planetary science literature from 2007 to 2011 reveals 106 uses of Alba Patera versus 5 for Alba Mons (accessed May 7, 2011).〕 The term Alba is from the Latin word for white and refers to the clouds frequently seen over the region from Earth-based telescopes.〔Hartmann, 2003, p. 308〕 The volcano was discovered by the Mariner 9 spacecraft in 1972 and was initially known as the Alba volcanic feature or the Arcadia Ring (in reference to the partial ring of fractures around the volcano). The IAU named the volcano Alba Patera in 1973.〔 The volcano is often simply called Alba when the context is understood. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Alba Mons」の詳細全文を読む スポンサード リンク
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