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

Tharsis Tharsis () is a vast volcanic plateau centered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Asc ...

bulge near the equator of the

planet A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury. In the English language, Mars is named for the Roman god of war. Mars is a terrestrial planet with a thin at ...

. To its north is

Pavonis Mons Pavonis Mons (Latin for "peacock mountain") is a large shield volcano located in the Tharsis region of the planet Mars. It is the middle member of a chain of three volcanic mountains (collectively known as the Tharsis Montes) that straddle th ...

, and north of that is

Ascraeus Mons 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. Discovery The volcano's location corresponds to t ...

. The tallest volcano in the

Solar System The Solar System Capitalization 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 "Solar ...

, Olympus Mons, is to its northwest. Its name comes from a corresponding albedo feature on a map by

Giovanni Schiaparelli Giovanni Virginio Schiaparelli ( , also , ; 14 March 1835 – 4 July 1910) was an Italian astronomer and science historian. Biography He studied at the University of Turin, graduating in 1854, and later did research at Berlin Observatory, ...

, which he named in turn after the legendary Roman forest of Arsia Silva.

Structure

Arsia Mons is a shield volcano 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 volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

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 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 1013.25 millibars, ...

lower than 107

pascals The pascal (symbol: Pa) is the unit of pressure in the International System of Units (SI), and is also used to quantify internal pressure, stress, Young's modulus, and ultimate tensile strength. The unit, named after Blaise Pascal, is defined ...

Martian 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 ( or ; Hawaiian: ; en, Long Mountain) is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean. The largest subaerial volcano (as opposed to subaqueous volcanoes) in both mass and ...

Hawaii Hawaii ( ; haw, Hawaii or ) is a state in the Western United States, located in the Pacific Ocean about from the U.S. mainland. It is the only U.S. state outside North America, the only state that is an archipelago, and the only state ...

, 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 is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

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 being conducted by the European Space Agency (ESA). The ''Mars Express'' mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally ref ...

. 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 (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large ...

, 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 200–300 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 Orographic lift occurs when an air mass is forced from a low elevation to a higher elevation as it moves over rising terrain. As the air mass gains altitude it quickly cools down adiabatically, which can raise the relative humidity to 100% and cr ...

, 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 The Medusae Fossae Formation is a large geological formation of probable volcanic origin on the planet Mars. It is named for the Medusa of Greek mythology. "Fossae" is Latin for "trenches". The formation is a collection of soft, easily eroded de ...

could have been formed from ancient volcanic ash from Apollinaris Mons, Arsia Mons, and possibly

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 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 Picture of the Day (APOD) is a website provided by NASA and Michigan Technological University (MTU). According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation writt ...

for 28 May 2007 * {{Authority control Mountains on Mars Shield volcanoes Volcanoes of Mars Phoenicis Lacus quadrangle