Arsia Mons
Template:Short description Template:Infobox feature on celestial object Arsia Mons Template:IPAc-en is the southernmost of three volcanoes (collectively known as Tharsis Montes) on the Tharsis bulge near the equator of the planet Mars. To its north is Pavonis Mons, and north of that is Ascraeus Mons. The tallest volcano in the Solar System, Olympus Mons, 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. Historically, it was known as Nodus Gordii ("Gordian knot") before being renamed.<ref>Template:Cite book</ref>
Structure
Arsia Mons is a shield volcano with a relatively low slope and a massive caldera at its summit. The southernmost of the three Tharsis Montes volcanoes, it is the only major Tharsis volcano south of the equator.<ref name="Carr 2006 Location Map">Template:Cite bookTemplate:Dead link</ref>
The volcano is Template:Convert in diameter, almost Template:Convert high (more than Template:Convert higher than the surrounding plains<ref>Catalog Page for PIA02337</ref>), and the summit caldera is 110 km (72 miles) wide.<ref>Catalog Page for PIA03948</ref> It experiences atmospheric pressure lower than 107 pascals<ref name="stanascr">Martian Weather Observation Template:Webarchive NASA MGS data 9.2 degrees S 238.2 degrees E 17757 meters 1.07 mbar</ref> at the summit. Excluding Olympus Mons, it is the largest known volcano in terms of volume. Arsia Mons has 30 times the volume of Mauna Loa in Hawaii, the largest volcano on the Earth.<ref>Template:Cite book</ref>
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.<ref>Catalog Page for PIA03799</ref> The caldera floor formed around 150 Mya ago.<ref name="Carr 2006 Age of Caldera">Template:Cite bookTemplate:Dead link</ref>
The shield is transected roughly northeast to southwest by a set of collapse features.<ref name="Carr 2006 Rift Zone">Template:Cite bookTemplate:Dead link</ref> 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 probe Mars Express. In 2004, a 3D map of this region was created at high resolution.<ref name="South Flank">Template:Cite web</ref> Cliffs, landslides, and numerous collapse features can be seen in 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.<ref name="Glaciers on Northwest Arsia">Template:Cite web</ref>
Possible plate tectonics
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 of plate tectonics, which on Earth makes chains of "hot spot" volcanoes.<ref>Template:Cite journal</ref><ref>Template:Cite web</ref><ref>Template:Cite journal</ref>
History
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.<ref name="Richardson2017">Template:Cite journal</ref> This low recent rate contrasts with an average rate of 270 km3/Ma over the volcano's inferred entire 3400 Ma history.<ref name="Cohen2017">Template:Cite journal</ref>
Weather
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. 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 this orographic 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 the Mars Express orbiter.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>
A study using a global climate model found that the Medusae Fossae Formation could have been formed from ancient volcanic ash from Apollinaris Mons, Arsia Mons, and possibly Pavonis Mons.<ref>Template:Cite journal</ref>
Glaciers
Recent work provides evidence for glaciers on Arsia Mons at both high<ref name="Glaciers on Arsia Mons">Template:Cite journal</ref> and low elevations.<ref name="Glaciers on Northwest Arsia" /> 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 from sublimating.<ref>Scanlon,K., J. Head, D. Marchant. 2015. REMNANT BURIED ICE IN THE ARSIA MONS FAN-SHAPED DEPOSIT, MARS. 46th Lunar and Planetary Science Conference. 2266.pdf</ref>
Possible cave entrances
As of 2007 seven putative cave entrances, have been identified in satellite imagery of the flanks of Arsia Mons.<ref>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)</ref><ref name = "Lakdawalla1">Template:Cite web</ref><ref name = "Lakdawalla2">Template:Cite web</ref> They have been informally dubbed Dena, Chloë, Wendy, Annie, Abbey, Nikki, and Jeanne and resemble "skylights" formed by the collapse of lava tube ceilings.
- Dena (Template:Coord)
- Chloë (Template:Coord)
- Wendy (Template:Coord)
- Annie (Template:Coord)
- Abbey and Nikki (Template:Coord)
- Jeanne (Template:Coord)
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 of Martian life.<ref>Template:Cite web</ref>
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.<ref>Template:Cite news</ref> Nonetheless, the darkness of this feature implies that it must be at least 178 meters deep.<ref>Template:Cite web</ref>
Gallery
-
Arsia Mons, as seen by THEMIS. Click on image to see relationship of Arsia Mons to other nearby volcanoes. -
Arsia Mons and its surroundings in a THEMIS daytime infrared image mosaic. A huge fan-shaped expanse of knobby deposits (the Arsia Sulci), believed left by past glaciation, extends northwestward from the mountain. -
Layers from numerous lava flows are exposed on the side of a pit on the lower west flank of Arsia Mons (photo by HiRISE). -
Possible cave entrance ("Jeanne") on Arsia Mons
See also
- Caves of Mars Project
- List of mountains on Mars by height
- List of tallest mountains in the Solar System
- Tharsis quadrangle
References
External links
- A Hole in Mars – Astronomy Picture of the Day for 28 May 2007
- Template:Gpn
- The Cave in Arsia Mons is a science fiction story by astronomer Andrew Fraknoi, published in the anthology Building Red
Template:Mars Template:Portal bar Template:Authority control