Arsia Mons is the southernmost of three volcanoes (collectively known as Tharsis Montes) on the Tharsis bulge near the

equator The equator is the circle of latitude that divides Earth into the Northern Hemisphere, Northern and Southern Hemisphere, Southern Hemispheres of Earth, hemispheres. It is an imaginary line located at 0 degrees latitude, about in circumferen ...

of the

planet A planet is a large, Hydrostatic equilibrium, rounded Astronomical object, astronomical body that is generally required to be in orbit around a star, stellar remnant, or brown dwarf, and is not one itself. The Solar System has eight planets b ...

Mars Mars is the fourth planet from the Sun. It is also known as the "Red Planet", because of its orange-red appearance. Mars is a desert-like rocky planet with a tenuous carbon dioxide () atmosphere. At the average surface level the atmosph ...

. To its north is Pavonis Mons, and north of that is Ascraeus Mons. The tallest volcano in the

Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Sola ...

Olympus Mons Olympus Mons (; ) is a large shield volcano on Mars. It is over high as measured by the Mars Orbiter Laser Altimeter (MOLA), about 2.5 times the elevation of Mount Everest above sea level. It is Mars's tallest volcano, its tallest planetary mou ...

, is to its northwest. Its name comes from a corresponding

albedo feature In planetary geology, an albedo feature is a large area on the surface of a planet (or other Solar System body) which shows a contrast in brightness or darkness (albedo) with adjacent areas. Historically, albedo features were the first (and usu ...

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 The cutting of the Gordian Knot is an Ancient Greek legend associated with Alexander the Great in Gordium in Phrygia, regarding a complex knot that tied an oxcart. Reputedly, whoever could untie it would be destined to rule all of Asia. In 33 ...

") before being renamed.

Structure

Arsia Mons is a

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...

with a relatively low slope and a massive

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

at its summit. The southernmost of the three Tharsis Montes volcanoes, it is the only major Tharsis volcano south of the equator. The volcano is in diameter, almost high (more than higher than the surrounding plains), and the summit

is 110 km (72 miles) wide. It experiences

atmospheric pressure Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth. The standard atmosphere (symbol: atm) is a unit of pressure defined as , which is equivalent to 1,013. ...

lower than 107 pascalsMartian Weather Observation
NASA MGS data 9.2 degrees S 238.2 degrees E 17757 meters 1.07 mbar 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 Mauna Loa (, ; ) is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean. Mauna Loa is Earth's largest active volcano by both mass and volume. It was historically considered to be the largest ...

Hawaii Hawaii ( ; ) is an island U.S. state, state of the United States, in the Pacific Ocean about southwest of the U.S. mainland. One of the two Non-contiguous United States, non-contiguous U.S. states (along with Alaska), it is the only sta ...

, the largest volcano on the Earth. The caldera of Arsia Mons was formed when the mountain collapsed in on itself after its reservoir of

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...

was exhausted. There are many other geologic collapse features on the mountain's flanks. The caldera floor formed around 150 Mya ago. The shield is transected roughly northeast to southwest by a set of collapse features. 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 ''Mars Express'' is a space exploration mission by the European Space Agency, European Space Agency (ESA) exploring the planet Mars and its moons since 2003, and the first planetary mission attempted by ESA. ''Mars Express'' consisted of two ...

. In 2004, a 3D map of this region was created at high resolution. Cliffs, landslides, and numerous collapse features can be see
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.

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 Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...

, which on Earth makes chains of "hot spot" volcanoes.

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. This low recent rate contrasts with an average rate of 270 km³/Ma over the volcano's inferred entire 3400 Ma history.

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

orbiter. 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.

Glaciers

Recent work provides evidence for glaciers on Arsia Mons at both high and low elevations. 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.

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, Chloë, Wendy, Annie, Abbey, Nikki, and Jeanne and resemble "skylights" formed by the collapse of

lava tube A lava tube, more rarely called a pyroduct, is a 'roofed conduit through which molten lava travels away from its vent'. If lava in the tube drains out, it will leave an empty cave. Lava tubes are common in low-viscosity volcanic systems. La ...

ceilings. *Dena () *Chloë () *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 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. 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 178 meters deep.

Gallery

File:Arsia Mons.JPG, Arsia Mons, as seen by THEMIS. Click on image to see relationship of Arsia Mons to other nearby volcanoes. File:Arsia Mons THEMIS day IR 100m v11.5 0.5.jpg, 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. File:PIA13540 - Layers in Martian volcano Arsia Mons.jpg, Layers from numerous lava flows are exposed on the side of a pit on the lower west flank of Arsia Mons (photo by HiRISE). File:Mars; Arsia Mons cave entrance -MRO.jpg, Possible cave entrance ("Jeanne") on Arsia Mons

References

External links

A Hole in Mars
–

Astronomy Picture of the Day Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include ...

for 28 May 2007 *
''The Cave in Arsia Mons''
is a science fiction story by astronomer

Andrew Fraknoi Andrew Fraknoi (born 1948) is a retired professor of astronomy recognized for his lifetime of work using everyday language to make astronomy more accessible and popular for both students and the general public. In 2017 Fraknoi retired from his po ...

, published in the anthology ''Building Red'' {{Authority control Mountains on Mars Shield volcanoes Volcanoes of Mars Phoenicis Lacus quadrangle