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Arsia Mons is the southernmost of three volcanos (collectively known as Tharsis Montesmarker) on the Tharsismarker bulge near the equator of the planet Mars. To its north is Pavonis Monsmarker, and north of that is Ascraeus Monsmarker. The tallest mountain in the solar system, Olympus Monsmarker, is to its northwest. Its name comes from a corresponding albedo feature on a map by Giovanni Schiaparelli, which he named in turn after the legendary Roman forest of Arsia Silva.

Arsia Mons is 270 miles (approximately 435 kilometres) in diameter, almost 12 miles high (more than 9 kilometers (5.6 miles) higher than the surrounding plains), and the summit caldera is 72 miles (approximately 110 km) wide. It experiences atmospheric pressure lower than 107 pascals at the summit. Except for Olympus Mons, it is the biggest volcano in volume.

Topographic map of Arsia Mons

A repeated weather phenomenon occurs each year near the start of southern winter over Arsia Mons. Just before southern winter begins, sunlight warms the air on the slopes of the volcano. This air rises, bringing small amounts of dust with it. Eventually the rising air converges over the volcano's caldera and the fine sediment blown up from the volcano's slopes coalesces into a spiraling cloud of dust that is thick enough to observe from orbit. The spiral dust cloud over Arsia Mons repeats each year, but observations and computer calculations indicate it can only form during a short period of time each year. Similar spiral clouds have not been seen over the other large Tharsis volcanoes, but other types of clouds have been seen. The spiral dust cloud over Arsia Mons can tower 15 to 30 kilometers (9 to 19 miles) above the volcano.

The caldera of Arsia Mons was formed when the mountain collapsed in on itself after its reservoir of magma was exhausted. There are many other geologic collapse features on the mountain's flanks.

Possible Plate Tectonics

Arsia Mons is the southernmost of three volcanos (collectively known as Tharsis Montes) on the Tharsis bulge near the equator of the planet Mars. The other Tharsis volcanoes are Ascraeus Mons and Pavonis Mons. The three Tharsis Montes, together with some smaller volcanoes to the north form a rather straight line. This arrangement suggests that they were formed by a crustal plate moving over a hot spot. Such an arrangement exists in the Earth's Pacific Oceanmarker, especially with the Hawaiian Islands. The Hawaiian Isands are in a straight line, with the youngest in the south and the oldest in the north. So geologists believe the plate is moving while a plume of hot magma rises, then punches through the crust to produce a volcanic mountain.

Image:Arsia Mons.JPG|Arsia Mons, as seen by THEMIS. Click on image to see relationship of Arisia Mons to other nearby volcanoes.

Image:Arsia Mons layers.jpg|Layers are visible in a pit on the lower flank of Arsia Mons. A dark streak is also visible. As seen by HiRISE.


Recent studies provide evidence for glaciers on Arsia Mons. A series of parallel ridges resemble moraines dropped by glaciers. Another section looks as if ice melted under the ground and formed a knobby terrain. A third bit of evidence is the lower part that has lobes and seems to be flowing onto the lower surface. This lobed feature probably still contains an ice core that is covered with a thin layer of rocks that keep the ice from sublimating (going directly from a solid to a gas due to present atmospheric conditions). Perhaps, in the future colonists will tap this ice for water.

Possible cave entrances

As of 2007 seven putative cave entrances have been identified in satellite imagery of the flanks of Arsia Mons. They have been informally dubbed Dena, Chloƫ, Wendy, Annie, Abbey, Nikki, and Jeanne and resemble "skylights" formed by the collapse of cave ceilings.
Mosaic image of Arsia Mons on Mars

  • Dena ( )
  • ChloĆ« ( )
  • Wendy ( )
  • Annie ( )
  • Abbey and Nikki ( )
  • Jeanne ( )

From day to night, temperatures of the circular features change only about one-third as much as the change in temperature of surrounding ground. While this is more variable than large caves on Earth, it is consistent with them being deep pits. However, due to the extreme altitude, it is unlikely that they will be able to harbour any form of Martian life.

A more recent photograph of one of the features shows sunlight illuminating a side wall, suggesting that it may simply be a vertical pit rather than an entrance to a larger underground space. Nonetheless, the darkness of this feature implies that it must be at least 78 metres deep.

See also


Possible cave entrance ("Jeanne") on Arsia Mons

  1. Catalog Page for PIA02337
  2. Catalog Page for PIA03948
  3. Martian Weather Observation NASA MGS data 9.2 degrees S 238.2 degrees E 17757 meters 1.07 mbar
  4. Catalog Page for PIA04294
  5. Catalog Page for PIA03799
  7. Themis Observes Possible Cave Skylights on Mars. G. E. Cushing, T. N. Titus, J. J. Wynne, P. R. Christensen. Lunar and Planetary Science XXXVIII (2007)

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