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Olympus Mons (Latin for "Mount Olympus") is the tallest known volcano and mountain in the Solar System and was formed during the Amazonian epoch. It is located on the planet Mars at approximately 18°N 133°W / 18, -133. It is three times as tall as Mount Everestmarker. Since the late 19th century — well before space probes confirmed its identity as a mountain — Olympus Mons was known to astronomers as the albedo feature, Nix Olympica ("Snows of Olympus"), although its mountainous nature was suspected.

General description

Olympus Mons
The central edifice stands 27 kilometers (around 16.7 miles/approx. 88,600 ft) high above the mean surface level of Mars (about three times the elevation of Mount Everestmarker above sea level and 2.6 times the height of Mauna Keamarker above its base). It is 550 km (342 miles) in width, flanked by steep cliffs, and has a caldera complex that is 85 km (53 miles) long, 60 km (37 miles) wide, and up to 3 km (1.8 miles) deep with six overlapping pit craters. Its outer edge is defined by an escarpment up to 6 km (4 miles) tall, unique among the shield volcanoes of Mars. For a size comparison Olympus Mons is approximately the size of the U.S. State of Missourimarker.

Both the size of Olympus Mons and its shallow slope (2.5 degrees central dome surrounded by 5 degree outer region) means that a person standing on the surface of Mars would be unable to view the upper profile of the volcano even from a distance, as the curvature of the planet and the volcano itself would obscure it. However, one could view parts of Olympus: standing on the highest point of its summit, the slope of the volcano would extend beyond the horizon, a mere 3 kilometers away; from the three kilometer elevated caldera rim one could see 80 kilometers to the caldera's other side; from the southeast scarp highpoint (about 5 km elevation) one could look about 180 km southeast; from the northwest scarp highpoint (about 8 km elevation) one could look upslope possibly 240 km and northeast up to 230 km.

An occasional misconception is that the top of Olympus Mons is above the Martian atmosphere. The atmospheric pressure at the top varies between 5 and 8% of the average Martian surface pressure (600 pascals); by comparison the atmospheric pressure at the summit of Mount Everestmarker is about 32 percent of that at sea level. Even so, airborne Martian dust is still present and high altitude carbon dioxide-ice cloud cover is still possible at the peak of Olympus Mons, though water-ice clouds are not. Although the average Martian surface atmospheric pressure is less than one percent of that seen on Earth, the much lower gravity on Mars allows its atmosphere to extend much higher, as lower gravity increases scale height.

Two of the craters on Olympus Mons have been provisionally assigned names by the IAU. These are the 15.6 km diameter Karzok crater ( ) and the 10.4 km diameter Pangboche crater ( ).

Volcanism

Olympus Mons is a shield volcano, the result of highly fluid lava flowing out of volcanic vents over a long period of time, and is much wider than it is tall; the average slope of Olympus Mons' flanks is very gradual. In 2004 the Mars Express orbiter imaged old lava flows on the flanks of Olympus Mons. Based on crater size and frequency counts, the surface of this western scarp has been dated from 115 million years old down to a region that is only 2 million years old. This is very recent in geological terms, suggesting that the mountain may yet have some ongoing volcanic activity.

The Hawaiian Islands are examples of similar shield volcanoes on a smaller scale (see Mauna Keamarker). The extraordinary size of Olympus Mons is likely because Mars does not have tectonic plates. Thus, the crust remained fixed over a hotspot and the volcano continued to discharge lava, bringing it to such a height.

The caldera at the peak of the volcano was formed after volcanism ceased and the roof of the emptied magma chamber collapsed. During the collapse the surface became extended and formed fractures. Later additional caldera collapses were formed due to subsequent lava production. These overlapped the original circular caldera, giving the edge a less symmetric appearance.

Early observations and naming

The mountain, as well as a few other of the volcanoes in the Tharsis regionmarker, has sufficient height to reach above the frequent dust storms of Mars, and it was visible from Earth already to 19th century observers. The astronomer Patrick Moore points out that during dust storms, "Schiaparelli had found that his Nodus Gordis and Olympic Snow were almost the only features to be seen. He guessed correctly that they must be high". Only with the Mariner probes could this be confirmed with certainty. After the Mariner 9 probe had photographed it from orbit in 1972, it became clear that the altitude was much greater than that of any mountain found on Earth, and the name was changed to Olympus Mons.

Surroundings

Olympus Mons is located in the Tharsis bulgemarker, a huge swelling in the Martian surface that bears numerous other large volcanic features. Among them are a chain of lesser shield volcanoes including Arsia Monsmarker, Pavonis Monsmarker and Ascraeus Monsmarker, which are small only in comparison to Olympus Mons itself. The land immediately surrounding Olympus Mons is a depression in the bulge 2 km deep.

The volcano is surrounded by a region known as the Olympus Mons aureole (Latin, "circle of light") with gigantic ridges and blocks extending 1000 km (600 miles) from the summit that show evidence of development and resurfacing connected with glacial activity. Both the escarpment and the aureole are poorly understood. In one theory, this basalt cliff was formed by landslides, and the aureole consists of material they deposited. A view of this escarpment (scarp/cliff) is shown in the picture taken by HiRISE below.

Image:Olympus Mons Scarp.JPG|Olympus Monsmarker Scarp, as seen by HiRISE. Scale bar is 500 meters long.

Image:Young and Old Lava Flows.JPG|Image shows both young and old lava flows from the base of Olympus Monsmarker. The flat plain is the younger flow. The older flow has channels with levees along their edges. The presence of levees is quite common in many lava flows. Image from Mars Global Surveyor.

See also



References

  1. Patrick Moore 1977, Guide to Mars, London (UK), Cutterworth Press, p.96
  2. Highest and lowest points on Mars NASA
  3. Martian Volcanoes on HST Images How Far Could I See Standing on Olympus Mons, "2.37 miles", Jeff Beish, Former A.L.P.O. Mars Recorder
  4. Spreading of the Olympus Mons volcanic edifice, Mars. P. J. McGovern lpi.usra.edu, 2005, Lunar and Planetary Science XXXVI (2005), Figure 2b showing profiles with NE and SW scarp highpoints
  5. Public Access to Standard Temperature-Pressure Profiles Standard Pressure Profiles measured by MGS Radio Science team at 27 km range from approx 30 to 50 pascals
  6. Late Martian Weather! stanford.edu temperature/pressure profiles 1998 to 2005
  7. Moore 1977, Guide to Mars, p.120


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