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| Feature type | Shield volcano |
|---|---|
| Coordinates | 8°21′S120°05′W / 8.35°S 120.09°W /-8.35; -120.09 |
| Peak | 11.7 km (7.3 mi) 38,386 ft (11,700 m) |
| Eponym | Latin –Arsia Silva – classical albedo feature name |
Arsia Mons/ˈɑːrsiəˈmɒnz/ is the southernmost of three volcanoes (collectively known asTharsis Montes) on theTharsis bulge near theequator of theplanetMars. To its north isPavonis Mons, and north of that isAscraeus Mons. The tallest volcano in theSolar System,Olympus Mons, is to its northwest. Its name comes from a correspondingalbedo feature on a map byGiovanni Schiaparelli, which he named in turn after the legendary Roman forest ofArsia Silva. Historically, it was known asNodus Gordii ("Gordian knot") before being renamed.[1]
Arsia Mons is ashield volcano with a relatively low slope and a massivecaldera at its summit. The southernmost of the threeTharsis Montes volcanoes, it is the only major Tharsis volcano south of the equator.[2]
The volcano is 435 kilometres (270 mi) in diameter, almost 20 kilometres (12 mi) high (more than 9 kilometers (5.6 mi) higher than the surrounding plains[3]), and the summitcaldera is 110 km (72 miles) wide.[4] It experiencesatmospheric pressure lower than 107pascals[5] at the summit. Excluding Olympus Mons, it is the largest known volcano in terms of volume. Arsia Mons has 30 times the volume ofMauna Loa inHawaii, the largest volcano on the Earth.[6]
The caldera of Arsia Mons was formed when the mountain collapsed in on itself after its reservoir ofmagma was exhausted. There are many other geologic collapse features on the mountain's flanks.[7] The caldera floor formed around 150 Mya ago.[8]
The shield is transected roughly northeast to southwest by a set of collapse features.[9] The collapse features on the shield are connected by a line of small shield volcanoes on the floor of the caldera. It is possible that this line represents a significant fault similar to others found on the Tharsis bulge. This fault may represent the source of the Arsia lavas.
The rift area to the southwest has been imaged in significant detail by the European Space Agency probeMars Express. In 2004, a 3D map of this region was created at high resolution.[10] Cliffs, landslides, and numerous collapse features can be seenin this detailed image. Combined with the extensive lava flows at the termination of the rift, this may reveal areas that drained the caldera lavas and contributed to the collapse.
The northwest flank of the volcano is significantly different and rougher than the southeast flank, and the features may represent evidence of glaciers.[11]
The three Tharsis Montes, together with some smaller volcanoes to the north, form a rather straight line. It has been proposed that these are the result ofplate tectonics, which on Earth makeschains of "hot spot" volcanoes.[12][13][14]
The most recent eruptive episode in the history of Arsia Mons, among the youngest on Mars, involved at least 29 vents within the caldera and also eruptions on the flank aprons along the north–south axis of the volcano. This activity is thought to have extended from 200 to 300 Ma to 10–90 Ma ago, peaking at 150 Ma with eruption rates in the caldera of 1–8 km3 per Ma.[15] This low recent rate contrasts with an average rate of 270 km3/Ma over the volcano's inferred entire 3400 Ma history.[16]
A repeatedweather 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. On the leeward slope, water ice condenses, forming a cloud which can extend westward for more than 1000 km. The autumn of 2018 saw a particularly pronounced version of thisorographic cloud, as the planet-wide dust storm finally subsided. The presence of some dust undoubtedly emphasised the phenomenon. This phenomenon has been repeatedly observed by theMars Express orbiter.[17][18]
A study using a global climate model found that theMedusae Fossae Formation could have been formed from ancient volcanic ash fromApollinaris Mons, Arsia Mons, and possiblyPavonis Mons.[19]
Recent work provides evidence for glaciers on Arsia Mons at both high[20] and low elevations.[11] 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. The lower part has lobes and seems to be flowing downhill. This lobed feature may still contain an ice core that is covered with a thin layer of rocks that has prevented ice fromsublimating.[21]
As of 2007 seven putative cave entrances, have been identified in satellite imagery of the flanks of Arsia Mons.[22][23][24] They have been informally dubbed Dena, Chloë, Wendy, Annie, Abbey, Nikki, and Jeanne and resemble "skylights" formed by the collapse oflava tube ceilings.
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 there being deep pits. However, due to the extreme altitude, it is unlikely that they will be able to harbour any form ofMartian life.[25]
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.[26] Nonetheless, the darkness of this feature implies that it must be at least 178 meters deep.[27]
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