Ascraeus Mons
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| Coordinates | 11°55′N 255°55′E / 11.92°N 255.92°ECoordinates: 11°55′N 255°55′E / 11.92°N 255.92°E |
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| Peak | 18,225 m (59,793 ft) above datum 15 km (49,000 ft) local relief |
| Discoverer | Mariner 9 |
| Eponym | Ascraeus Lacus |
Ascraeus Mons is a large shield volcano located in the Tharsis region of the planet Mars. It is the northernmost and tallest of three shield volcanoes collectively known as the Tharsis Montes.
The volcano's location corresponds to the classical albedo feature Ascraeus Lacus.
Ascraeus Mons was discovered by the Mariner 9 spacecraft in 1971. The volcano was originally called North Spot because it was the northernmost of only four spots visible on the surface due to a global dust storm that was then enshrouding the planet. As the dust cleared, the spots were revealed to be extremely tall volcanoes whose summits had projected above the dust-laden, lower atmosphere.
The volcano's location corresponds to the classical albedo feature Ascraeus Lacus. The name comes from "Ascra," the birthplace of Hesiod. The word ascraeus is poetic for rural. The volcano's name officially became Ascraeus Mons in 1973.
The volcano is located in the southeast-central portion of the Tharsis quadrangle at 11.8°N, 255.5°E in Mars' western hemisphere. A group of three smaller volcanoes (the Ceraunius-Uranius group) lies about 700 km to the northeast, and Pavonis Mons (the middle volcano of the Tharsis Montes) lies 500 km to the southwest. The 70-km diameter crater Poynting is located 300 km to the west-southwest.
Ascraeus Mons is roughly 480 km in diameter and is the second highest mountain on Mars, with a summit elevation of 18.1 km. The volcano has a very low profile with an average flank slope of 7°. Slopes are steepest in the middle portion of the flanks, flattening out toward the base and near the top where a broad summit plateau and caldera (collapse crater) complex are located.
Volcanic vents, located on the northeastern and southwestern edges of the volcano, are sources for broad lava aprons, or fans, that bury nearby portions of the volcano and extend over 100 km out into the surrounding plains. The southwest-northeast orientation of the aprons matches the orientation of the Tharsis Montes, suggesting that a major fissure or rift in the Martian crust is responsible for the orientation of both the aprons and the Tharsis Montes chain. The presence of the lava aprons causes some disagreement in the actual dimensions of the volcano. If the aprons are included as part of the edifice then Ascraeus Mons has dimensions closer to 375 × 870 km.
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