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Tharsis Tholus is an intermediate-sized shield volcano located in the eastern Tharsis region of the planet Mars. The volcano was discovered by the Mariner 9 spacecraft in 1972〔Carr, M.H. (1973). Volcanism on Mars.'' J. Geophys. Res.'' 78(20), p. 4050, Fig. 1.〕 and originally given the informal name Volcano 7.〔''National Geographic'' (1973) Mars Map Supplement; February, 143(2), p. 255A.〕 In 1973, the International Astronomical Union (IAU) officially designated it Tharsis Tholus.〔 In planetary geology, tholus (pl. ''tholi'') is the term for a small domical mountain, usually a volcano.〔Hartmann, W.K. (2003). ''A Traveler's Guide to Mars: The Mysterious Landscapes of the Red Planet;'' Workman: New York, p. 28.〕 ==General Description== Tharsis Tholus lies on the eastern edge of the Tharsis quadrangle at 13.5°N, 91°W. It is about 800 km east-northeast of Ascraeus Mons,〔Platz, T. et al. (2009). Growth and Destruction Cycles and Eruption Styles at Tharsis Tholus, Mars. 40th Lunar and Planetary Science Conference; LPI: Houston, Abstract #1522. http://www.lpi.usra.edu/meetings/lpsc2009/pdf/1522.pdf.〕 the northernmost of the large Tharsis Montes volcanoes. Lava from the Tharsis Montes and other sources within the interior of Tharsis completely surrounds Tharsis Tholus, forming a broad volcanic plain at the volcano's base. Tharsis Tholus measures 155 km x 125 km.〔 It is distinctly bulbous in appearance, and is unique among Martian volcanoes in the degree to which it has been modified by faulting.〔Plescia, J.B. (2001). Geology of Tharsis Tholus, Mars. 32nd Lunar and Planetary Science Conference, LPI: Houston, Abstract #1090, p. 1. http://www.lpi.usra.edu/meetings/lpsc2001/pdf/1090.pdf.〕 Large normal faults cut across and completely penetrate the volcano, dividing the edifice into several major blocks, or sectors. The volcano has an elongated central caldera (collapse crater) measuring 36.7 × 38.9 km and about 3 km deep. In profile, Tharsis Tholus is dome-shaped (convex upward),〔Carr, M.H. (2006). ''The Surface of Mars;'' Cambridge University Press: Cambridge, UK, p. 57.〕 with flank slopes ranging from less than 1° near the summit to up to 16° at the base.〔 The average flank slope is 10°, making it one of the steepest volcanoes on Mars. The volcano rises to an elevation of about . The base of the volcano is buried by young (Amazonian-aged) lava flows presumably from the Tharsis Montes, so the true size of the edifice cannot be accurately determined. Estimates of the thickness of lava burying the base of Tharsis Tholus range from 500 m〔 to 3.5 km.〔Robinson, M. (1993) PhD dissertation cited by Plescia (2003), p. 236.〕 Most of the volcano's surface is mantled with a thick layer of fine dust or ash,〔 giving the volcano's flanks a smooth to slightly hummocky appearance.〔 The mantle material obscures the underlying bedrock except in areas with steep slopes, such as along the caldera's upper walls. Landslide debris from the caldera's western and southeastern wall is present on the floor of the caldera. 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「Tharsis Tholus」の詳細全文を読む スポンサード リンク
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