Tharsis
Encyclopedia
The Tharsis region on Mars
is a vast volcanic plateau
centered near the equator in Mars’ western hemisphere. The region is home to the largest volcanoes in the Solar System
, including the three enormous shield volcano
es Arsia Mons
, Pavonis Mons
, and Ascraeus Mons
, which are collectively known as the Tharsis Montes
. The tallest volcano on the planet, Olympus Mons
, is often associated with the Tharsis region but is actually located off the western edge of the plateau. The name Tharsis is the Greco-Latin transliteration
of the biblical Tarshish
, the land at western extremity of the known world.
-sized region of anomalously elevated terrain centered just south of the equator around longitude 265°E. Called the Tharsis bulge or Tharsis rise, this broad, elevated region dominates the western hemisphere of Mars and is the largest topographic
feature on the planet, after the global dichotomy
.
Tharsis has no formally defined boundaries, so precise dimensions for the region are difficult to give. In general, the bulge is about 5,000 km across and up to 7 km high (excluding the volcanoes, which have much higher elevations). It roughly extends from Amazonis Planitia
(215°E) in the west to Chryse Planitia
(300°E) in the east. The bulge is slightly elongated in the north-south direction, running from the northern flanks of Alba Patera
(about 55°N) to the southern base of the Thaumasia
highlands (about 43°S). Depending on how the region is defined, Tharsis covers 10–30 million km2, or up to 25% of Mars’ surface area.
Tharsis is divided into two broad rises, a northern and a larger southern rise. The northern rise partially overlies sparsely cratered, lowland plains north of the dichotomy
boundary. This region is dominated by Alba Patera
and its extensive volcanic flows. Alba Patera is a vast, low-lying volcanic construct that is unique to Mars. Alba Patera is so large and topographically distinct that it can almost be treated as an entire volcanic province onto itself. The oldest part of the northern rise consists of a broad topographic ridge that corresponds to the highly fractured terrain of Ceraunius Fossae
. The ridge is oriented north-south and forms part of the Noachian-aged basement on which Alba Patera sits. Also located in the northern rise are lava flows of the Ceraunius Fossae Formation, which are somewhat older than the Amazonian-aged flows that make up much of the central Tharsis region to the south.
The larger southern portion of Tharsis (pictured right) lies on old cratered highland terrain. Its western boundary is roughly defined by the high lava plains of Daedalia Planum
, which slope gently to the southwest into the Memnonia and Terra Sirenum
regions. To the east, the southern Tharsis buldge consists of the vast Syria-Thaumasia block, an enigmatic, roughly rectangular slab of uplifted crust about 3,000 km wide. The Syria-Thaumasia block is bounded to the west by a highly elevated zone of fractures (Claritas Fossae
) and mountains (the Thaumasia Highlands) that curves south then east to northeast in a wide arc that has been compared to the shape of a scorpion’s tail. Syria-Thaumasia is bounded to the north by Noctis Labyrinthus
and the western three-quarters of Valles Marineris
. It is bounded to the east by a north-south oriented ridge called the Coprates rise. These boundaries enclose a broad high plateau and shallow interior basin that include Syria
, Sinai, and Solis Plana (see list of plains on Mars). The highest plateau elevations on the Tharsis buldge occur in northern Syria Planum
, western Noctis Labyrinthus
, and the plains east of Arsia Mons
.
Between the northern and southern portions of the Tharsis bulge lies a relatively narrow, northeast-trending region that may be considered Tharsis proper or central Tharsis. It is defined by the three massive Tharsis Montes
volcanoes (Arsia Mons
, Pavonis Mons
, and Ascraeus Mons
), a number of smaller volcanic edifices, and adjacent plains consisting of young (mid to late Amazonian) lava flows. The lava plains slope gently to the east where they overlap and embay the older (Hesperian-aged) terrain of Echus Chasma
and western Tempe Terra
. To the west, the lava plains slope toward a system of immense northwest-oriented valleys that are up to 200 km wide. These northwestern slope valleys (NSVs), which debouch
into Amazonis Planitia
, are separated by a parallel set of gigantic "keel-shaped" prominatories. The NSVs may be relicts from catastrophic floods of water, similar to the huge outflow channels that empty into Chryse Planitia, east of Tharsis. The area of central Tharsis is approximately 3500 km long and includes most of the region covered by the Tharsis quadrangle
and the northwestern portion of the adjoining Phoenicis Lacus quadrangle
to the south.
Finally, the massive Olympus Mons
and its associated lava flows and aureole deposits form another distinct subprovince of the Tharsis region. This subregion is about 1600 km across. It lies off the main topographic buldge, but is clearly related to the volcanic processes that formed Tharsis. Olympus Mons is the youngest of the large Tharsis volcanoes.
and associated tectonic processes that have caused extensive crustal deformation. According to the standard view, Tharsis overlies a hot spot
, similar to the one thought to underlie the island of Hawaii
. The hot spot is caused by one or more massive columns of hot, low-density material (a superplume) rising through the mantle. The hot spot produces voluminous quantities of magma
in the lower crust that is released to the surface as highly fluid, basalt
ic lava
. Because Mars lacks plate tectonics
, the lava is able to build up in one region for billions of years to produce enormous volcanic constructs.
On Earth (and presumably Mars as well), not all of the magma produced in a large igneous province
erupts at the surface as lava. Much of it stalls in the crust where it slowly cools and solidifies to produce large intrusive complexes (pluton
s). If the magma migrates through vertical fractures it produces swarms of dikes
that may be expressed at the surface as long, linear cracks (fossae) and crater chain
s (catena
e). Magma may also intrude the crust horizontally as large tabular bodies, such as sills
and laccolith
s, that can cause a general doming and fracturing of the overlying crust. Thus, the bulk of Tharsis is probably made of these intrusive complexes in addition to lava flows at the surface.
One key question about the nature of Tharsis has been whether the bulge is mainly the product of active crustal uplifting from buoyancy
provided by the underlying mantle plume or whether it is merely a large, static mass of igneous material supported by the underlying lithosphere
. Theoretical analysis of gravity data and the pattern of faults surrounding Tharsis suggest the latter is more likely. The enormous sagging weight of Tharsis has generated tremendous stresses in the crust, producing a broad trough around the region and an array of radial fractures emanating from the center of the bulge that stretches halfway across the planet.
Geologic evidence, such as the flow direction of ancient valley networks around Tharsis, indicates that the bulge was largely in place by the end of the Noachian Period, some 3.7 billion years ago. Although the bulge itself is ancient, volcanic eruptions in the region continued throughout Martian history and probably played a significant role in the production of the planet's atmosphere and the weathering of rocks on the planet's surface. By one estimate, the Tharsis buldge contains around 300 million km3 of igneous material. Assuming the magma that formed Tharsis contained carbon dioxide
(CO2) and water vapor in percentages comparable to that observed in Hawaiian basaltic lava, then the total amount of gases released from Tharsis magmas could have produced a 1.5-bar CO2 atmosphere and a global layer of water 120 m thick. Martian magmas also likely contain significant amounts of sulfur
and chlorine
. These elements combine with water to produce acids that can break down primary rocks and minerals. Exhalations from Tharsis and other volcanic centers on the planet are likely responsible for an early period of Martian time (the Theiikian) when sulfuric acid
weathering
produced abundant hydrated sulfate minerals such as kieserite
and gypsum
.
The total mass of the Tharsis bulge is approximately 1021 kg, about the same as the dwarf planet
Ceres
. Tharsis is so large and massive that it has likely affected the planet's moment of inertia
, possibly causing a change in the orientation of the planet's crust with respect to its rotational axis over time. According to one recent study, Tharsis originally formed at about 50°N latitude and migrated toward the equator between 4.2 and 3.9 billion years ago. Such shifts, known as true polar wander
, would have caused dramatic climate changes over vast areas of the planet.
to incorporate geologic features of widely different shapes, sizes, and compositions throughout the Solar System.One surprising and controversial conclusion from this synthesis of ideas is that the Tharsis region may be a single giant volcano. This is the thesis of geologists Andrea Borgia and John Murray in a Geological Society of America
special paper published in 2010.
The key to understanding how a vast igneous province like Tharsis can itself be a volcano is to re-think the notion of volcano from one of simple conical edifice to that of an environment or "holistic" system. According to the conventional view in geology, volcanoes passively build up from lava and ash erupted above fissures or rifts in the crust. The rifts are produced through regional tectonic forces operating in the crust and underlying mantle. Traditionally, the volcano and its magmatic plumbing have been studied by volcanologists and igneous petrologists
, while the tectonic features are the subject for structural geologists
and geophysicists
. However, recent work on large terrestrial volcanoes indicates that the distinction between volcanic and tectonic
processes is quite blurry, with significant interplay between the two.
Many volcanoes produce deformational structures
as they grow. The flanks of volcanoes commonly exhibit shallow gravity slumps, faults and associated folds
. Large volcanoes grow not only by adding erupted material to their flanks, but also by spreading laterally at their bases, particularly if they rest on weak or ductile materials. As a volcano grows in size and weight, the stress field underneath the volcano changes from compressional to extensional. A subterranean rift may develop at the base of the volcano where the crust is wrenched apart. This volcanic spreading may initiate further structural deformation in the form of thrust fault
s along the volcano's distal flanks, pervasive graben
s and normal faults across the edifice, and catastrophic flank failure (sector collapse). Mathematical analysis shows that volcanic spreading operates on volcanoes at a wide range of scales and is theoretically similar to the larger-scale rifting that occurs at mid-ocean ridge
s (divergent plate boundaries
). Thus, in this view, the distinction between tectonic plate
, spreading volcano, and rift is nebulous, all being part of the same geodynamic system.
According to Borgia and Murray, Mt. Etna in Sicily
is a good terrestrial analogue
for the much larger Tharsis bulge, which to them is one immense volcano they call Tharsis Rise. Mt. Etna is a complex spreading volcano that is characterized by three main structural features: a volcanic rift system that crosses the summit in a north-northeast direction; a peripheral compression belt (thrust front) surrounding the base of the volcano; and a east-northeast trending system of transtensional (oblique normal) faults that connect the summit rift to the peripheral thrust front. The volcano's peak contains an array of steep summit cones, which are frequently active. The entire edifice is also peppered with a large number of small parasitic cones.
The structural similarities of Etna to Tharsis Rise are striking, even though the latter is some 200 times larger. In Borgia and Murray's view, Tharsis resembles a very large spreading volcano. As with Etna, the spreading has produced a rift through the summit of the rise and a system of radial tear faults that connect the rift to a basal compression belt. The tear-fault system on Tharsis is represented by the radial fossae, of which Valles Marineris
is the largest example. The thrust front is visible as the Thaumasia Highlands. Unlike on Earth, where the rifting of plates produces a corresponding subduction zone, the thick lithosphere of Mars is unable to descend into the mantle. Instead, the compressed zone is scrunched up and sheared laterally into mountain ranges, in a process called obduction
. To complete the analogy, the huge Olympus Mons and the Tharsis Montes are merely summit cones or parasitic cones on a much larger volcanic edifice.
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
is a vast volcanic plateau
Volcanic plateau
A volcanic plateau is a plateau produced by volcanic activity. There are two main types: lava plateaus and pyroclastic plateaus.-Lava plateau:...
centered near the equator in Mars’ western hemisphere. The region is home to the largest volcanoes in the Solar System
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
, including the three enormous shield volcano
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
es Arsia Mons
Arsia Mons
Arsia Mons is the southernmost of three volcanos 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 mountain in the solar system, Olympus Mons, is to its northwest...
, Pavonis Mons
Pavonis Mons
Pavonis Mons 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 that straddle the Martian equator between longitudes 235°E and 259°E. The volcano was discovered by the Mariner 9 spacecraft in 1971 and was...
, and Ascraeus Mons
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. The volcano's location corresponds to the classical albedo feature Ascraeus Lacus.Ascraeus Mons was...
, which are collectively known as the Tharsis Montes
Tharsis Montes
The Tharsis Montes are three large shield volcanoes in the Tharsis region of the planet Mars. From north to south, the volcanoes are Ascraeus Mons, Pavonis Mons and Arsia Mons. Mons is the Latin word for mountain...
. The tallest volcano on the planet, Olympus Mons
Olympus Mons
Olympus Mons is a large volcanic mountain on the planet Mars. At a height of almost , it is one of the tallest mountains in the Solar System, three times as tall as Mount Everest and more than twice the height of Mauna Kea the tallest mountain on Earth. Olympus Mons is the youngest of the large...
, is often associated with the Tharsis region but is actually located off the western edge of the plateau. The name Tharsis is the Greco-Latin transliteration
Transliteration
Transliteration is a subset of the science of hermeneutics. It is a form of translation, and is the practice of converting a text from one script into another...
of the biblical Tarshish
Tarshish
Tarshish תַּרְשִׁישׁ occurs in the Hebrew Bible with several uncertain meanings:*One of the sons of Javan .* In the Bible Solomon set up a trade with Tarshish and received ivory, apes, and peacocks from Tarshish which are all native to the jungles in India. India's state bird for example is the...
, the land at western extremity of the known world.
Location and Size
The Tharsis region can have several meanings depending on historical and scientific context. The name is commonly used in a broad sense to represent a continentContinent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
-sized region of anomalously elevated terrain centered just south of the equator around longitude 265°E. Called the Tharsis bulge or Tharsis rise, this broad, elevated region dominates the western hemisphere of Mars and is the largest topographic
Topography
Topography is the study of Earth's surface shape and features or those ofplanets, moons, and asteroids...
feature on the planet, after the global dichotomy
Martian dichotomy
The most conspicuous feature of Martian surface geology is a sharp contrast, known as the Martian dichotomy, between the rugged southern highlands and the relatively smooth northern basins. The two hemispheres differ in elevation by 1 to 3 km...
.
Tharsis has no formally defined boundaries, so precise dimensions for the region are difficult to give. In general, the bulge is about 5,000 km across and up to 7 km high (excluding the volcanoes, which have much higher elevations). It roughly extends from Amazonis Planitia
Amazonis Planitia
Amazonis Planitia is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces to the west of Olympus Mons in the Valles Marineris region of the Memnonia quadrangle, centered at...
(215°E) in the west to Chryse Planitia
Chryse Planitia
Chryse Planitia is a smooth circular plain in the northern equatorial region of Mars close to the Tharsis region to the west, centered at . Chryse Planitia lies partially in the Lunae Palus quadrangle and partially in the Oxia Palus quadrangle...
(300°E) in the east. The bulge is slightly elongated in the north-south direction, running from the northern flanks of Alba Patera
Alba Patera
Alba Mons is an immense, low-lying volcano located in the northern Tharsis region of the planet Mars. It is the largest volcano on Mars in terms of area, with volcanic flow fields that extend for at least 1350 km from its summit...
(about 55°N) to the southern base of the Thaumasia
Thaumasia quadrangle
The Thaumasia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey Astrogeology Research Program...
highlands (about 43°S). Depending on how the region is defined, Tharsis covers 10–30 million km2, or up to 25% of Mars’ surface area.
Subprovinces
The greater Tharsis region consists of several geologically distinct subprovinces with different ages and volcano-tectonic histories. The subdivisions given here are informal and may comprise all or parts of other formally named physiographic features and regions.Tharsis is divided into two broad rises, a northern and a larger southern rise. The northern rise partially overlies sparsely cratered, lowland plains north of the dichotomy
Martian dichotomy
The most conspicuous feature of Martian surface geology is a sharp contrast, known as the Martian dichotomy, between the rugged southern highlands and the relatively smooth northern basins. The two hemispheres differ in elevation by 1 to 3 km...
boundary. This region is dominated by Alba Patera
Alba Patera
Alba Mons is an immense, low-lying volcano located in the northern Tharsis region of the planet Mars. It is the largest volcano on Mars in terms of area, with volcanic flow fields that extend for at least 1350 km from its summit...
and its extensive volcanic flows. Alba Patera is a vast, low-lying volcanic construct that is unique to Mars. Alba Patera is so large and topographically distinct that it can almost be treated as an entire volcanic province onto itself. The oldest part of the northern rise consists of a broad topographic ridge that corresponds to the highly fractured terrain of Ceraunius Fossae
Ceraunius Fossae
Ceraunius Fossae is an area of intensely fractured terrain in the northern Tharsis region of Mars. It lies directly south of the large volcano Alba Mons and consists of ancient highland crust that has been deformed by numerous parallel faults and tension cracks...
. The ridge is oriented north-south and forms part of the Noachian-aged basement on which Alba Patera sits. Also located in the northern rise are lava flows of the Ceraunius Fossae Formation, which are somewhat older than the Amazonian-aged flows that make up much of the central Tharsis region to the south.
The larger southern portion of Tharsis (pictured right) lies on old cratered highland terrain. Its western boundary is roughly defined by the high lava plains of Daedalia Planum
Daedalia Planum
Daedalia Planum is a plain on Mars located south of Arsia Mons at and appears to be relatively featureless plain with multiple lava flows and small craters...
, which slope gently to the southwest into the Memnonia and Terra Sirenum
Terra Sirenum
Terra Sirenum is a large region in the southern hemisphere of the planet Mars. It is centered at and covers 3900 km at its broadest extent. It covers latitudes 10 to 70 South and longitudes 110 to 180 W. Terra Sirenum is an upland area notable for massive cratering including the large Newton...
regions. To the east, the southern Tharsis buldge consists of the vast Syria-Thaumasia block, an enigmatic, roughly rectangular slab of uplifted crust about 3,000 km wide. The Syria-Thaumasia block is bounded to the west by a highly elevated zone of fractures (Claritas Fossae
Claritas Fossae
Claritas Fossae is a trough in the Phoenicis Lacus quadrangle of Mars, located at31.5 S and 104.1 W. It is 2,050.0 km long and was named after a classical albedo feature name....
) and mountains (the Thaumasia Highlands) that curves south then east to northeast in a wide arc that has been compared to the shape of a scorpion’s tail. Syria-Thaumasia is bounded to the north by Noctis Labyrinthus
Noctis Labyrinthus
Noctis Labyrinthus, "the labyrinth of the night", is a region of Mars between the Valles Marineris and the Tharsis upland. It is located in the Phoenicis Lacus quadrangle. The region is notable for its maze-like system of deep, steep-walled valleys...
and the western three-quarters of Valles Marineris
Valles Marineris
Valles Marineris is a system of canyons that runs along the Martian surface east of the Tharsis region...
. It is bounded to the east by a north-south oriented ridge called the Coprates rise. These boundaries enclose a broad high plateau and shallow interior basin that include Syria
Syria Planum
Syria Planum is a broad plateau on surface of Mars, forming part of Tharsis region. It is located at the summit of the Tharsis bulge, and was the center of volcanic and tectonic activity in Martian history from the Noachian to the late Hesperian. It has been confirmed that low shield volcanoes...
, Sinai, and Solis Plana (see list of plains on Mars). The highest plateau elevations on the Tharsis buldge occur in northern Syria Planum
Syria Planum
Syria Planum is a broad plateau on surface of Mars, forming part of Tharsis region. It is located at the summit of the Tharsis bulge, and was the center of volcanic and tectonic activity in Martian history from the Noachian to the late Hesperian. It has been confirmed that low shield volcanoes...
, western Noctis Labyrinthus
Noctis Labyrinthus
Noctis Labyrinthus, "the labyrinth of the night", is a region of Mars between the Valles Marineris and the Tharsis upland. It is located in the Phoenicis Lacus quadrangle. The region is notable for its maze-like system of deep, steep-walled valleys...
, and the plains east of Arsia Mons
Arsia Mons
Arsia Mons is the southernmost of three volcanos 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 mountain in the solar system, Olympus Mons, is to its northwest...
.
Between the northern and southern portions of the Tharsis bulge lies a relatively narrow, northeast-trending region that may be considered Tharsis proper or central Tharsis. It is defined by the three massive Tharsis Montes
Tharsis Montes
The Tharsis Montes are three large shield volcanoes in the Tharsis region of the planet Mars. From north to south, the volcanoes are Ascraeus Mons, Pavonis Mons and Arsia Mons. Mons is the Latin word for mountain...
volcanoes (Arsia Mons
Arsia Mons
Arsia Mons is the southernmost of three volcanos 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 mountain in the solar system, Olympus Mons, is to its northwest...
, Pavonis Mons
Pavonis Mons
Pavonis Mons 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 that straddle the Martian equator between longitudes 235°E and 259°E. The volcano was discovered by the Mariner 9 spacecraft in 1971 and was...
, and Ascraeus Mons
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. The volcano's location corresponds to the classical albedo feature Ascraeus Lacus.Ascraeus Mons was...
), a number of smaller volcanic edifices, and adjacent plains consisting of young (mid to late Amazonian) lava flows. The lava plains slope gently to the east where they overlap and embay the older (Hesperian-aged) terrain of Echus Chasma
Echus Chasma
Echus Chasma is a chasma in the Lunae Planum high plateau north of the Valles Marineris canyon system of Mars. Clay has been found in Echus Chasma that means that water once sat there for a time.-Geography:...
and western Tempe Terra
Tempe Terra
Tempe Terra is a heavily cratered highland region in the northern hemisphere of the planet Mars. Located at the northeastern edge of the Tharsis volcanic province, Tempe Terra is notable for its high degree of crustal fracturing and deformation...
. To the west, the lava plains slope toward a system of immense northwest-oriented valleys that are up to 200 km wide. These northwestern slope valleys (NSVs), which debouch
Debouch
Debouch is a term used in river and stream geography, and the military.-Geography:In fluvial geography, a debouch is a place where a body of water pours forth from a narrow opening...
into Amazonis Planitia
Amazonis Planitia
Amazonis Planitia is one of the smoothest plains on Mars. It is located between the Tharsis and Elysium volcanic provinces to the west of Olympus Mons in the Valles Marineris region of the Memnonia quadrangle, centered at...
, are separated by a parallel set of gigantic "keel-shaped" prominatories. The NSVs may be relicts from catastrophic floods of water, similar to the huge outflow channels that empty into Chryse Planitia, east of Tharsis. The area of central Tharsis is approximately 3500 km long and includes most of the region covered by the Tharsis quadrangle
Tharsis quadrangle
The Tharsis quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey Astrogeology Research Program. The Tharsis quadrangle is also referred to as MC-9 ....
and the northwestern portion of the adjoining Phoenicis Lacus quadrangle
Phoenicis Lacus quadrangle
The Phoenicis Lacus quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey Astrogeology Research Program. The Phoenicis Lacus quadrangle is also referred to as MC-17 ....
to the south.
Finally, the massive Olympus Mons
Olympus Mons
Olympus Mons is a large volcanic mountain on the planet Mars. At a height of almost , it is one of the tallest mountains in the Solar System, three times as tall as Mount Everest and more than twice the height of Mauna Kea the tallest mountain on Earth. Olympus Mons is the youngest of the large...
and its associated lava flows and aureole deposits form another distinct subprovince of the Tharsis region. This subregion is about 1600 km across. It lies off the main topographic buldge, but is clearly related to the volcanic processes that formed Tharsis. Olympus Mons is the youngest of the large Tharsis volcanoes.
Geology
Tharsis is commonly called a volcano-tectonic province, meaning that it is the product of volcanismVolcanism
Volcanism is the phenomenon connected with volcanoes and volcanic activity. It includes all phenomena resulting from and causing magma within the crust or mantle of a planet to rise through the crust and form volcanic rocks on the surface....
and associated tectonic processes that have caused extensive crustal deformation. According to the standard view, Tharsis overlies a hot spot
Hotspot (geology)
The places known as hotspots or hot spots in geology are volcanic regions thought to be fed by underlying mantle that is anomalously hot compared with the mantle elsewhere. They may be on, near to, or far from tectonic plate boundaries. There are two hypotheses to explain them...
, similar to the one thought to underlie the island of Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. The hot spot is caused by one or more massive columns of hot, low-density material (a superplume) rising through the mantle. The hot spot produces voluminous quantities of magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
in the lower crust that is released to the surface as highly fluid, basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
. Because Mars lacks plate tectonics
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
, the lava is able to build up in one region for billions of years to produce enormous volcanic constructs.
On Earth (and presumably Mars as well), not all of the magma produced in a large igneous province
Large igneous province
A Large Igneous Province is an extremely large accumulation of igneous rocks—intrusive, extrusive, or both—in the earth's crust...
erupts at the surface as lava. Much of it stalls in the crust where it slowly cools and solidifies to produce large intrusive complexes (pluton
Pluton
A pluton in geology is a body of intrusive igneous rock that crystallized from magma slowly cooling below the surface of the Earth. Plutons include batholiths, dikes, sills, laccoliths, lopoliths, and other igneous bodies...
s). If the magma migrates through vertical fractures it produces swarms of dikes
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
that may be expressed at the surface as long, linear cracks (fossae) and crater chain
Crater chain
A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena , as specified by the International Astronomical Union's rules on planetary nomenclature....
s (catena
Catena
The word catena has various meanings:*The Latin word for "chain"*Catena *Catenary, a type of curve in mathematics*A chain of similarly sized impact craters, in planetary geology...
e). Magma may also intrude the crust horizontally as large tabular bodies, such as sills
Sill (geology)
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet...
and laccolith
Laccolith
A laccolith is a sheet intrusion that has been injected between two layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base.Laccoliths tend to form at relatively...
s, that can cause a general doming and fracturing of the overlying crust. Thus, the bulk of Tharsis is probably made of these intrusive complexes in addition to lava flows at the surface.
One key question about the nature of Tharsis has been whether the bulge is mainly the product of active crustal uplifting from buoyancy
Buoyancy
In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...
provided by the underlying mantle plume or whether it is merely a large, static mass of igneous material supported by the underlying lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
. Theoretical analysis of gravity data and the pattern of faults surrounding Tharsis suggest the latter is more likely. The enormous sagging weight of Tharsis has generated tremendous stresses in the crust, producing a broad trough around the region and an array of radial fractures emanating from the center of the bulge that stretches halfway across the planet.
Geologic evidence, such as the flow direction of ancient valley networks around Tharsis, indicates that the bulge was largely in place by the end of the Noachian Period, some 3.7 billion years ago. Although the bulge itself is ancient, volcanic eruptions in the region continued throughout Martian history and probably played a significant role in the production of the planet's atmosphere and the weathering of rocks on the planet's surface. By one estimate, the Tharsis buldge contains around 300 million km3 of igneous material. Assuming the magma that formed Tharsis contained carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
(CO2) and water vapor in percentages comparable to that observed in Hawaiian basaltic lava, then the total amount of gases released from Tharsis magmas could have produced a 1.5-bar CO2 atmosphere and a global layer of water 120 m thick. Martian magmas also likely contain significant amounts of sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
. These elements combine with water to produce acids that can break down primary rocks and minerals. Exhalations from Tharsis and other volcanic centers on the planet are likely responsible for an early period of Martian time (the Theiikian) when sulfuric acid
Sulfuric acid
Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...
weathering
Weathering
Weathering is the breaking down of rocks, soils and minerals as well as artificial materials through contact with the Earth's atmosphere, biota and waters...
produced abundant hydrated sulfate minerals such as kieserite
Kieserite
Kieserite is a highly unstable magnesium sulfate mineral . It has a vitreous luster and it is colorless, grayish-white or yellowish. Its hardness is 3.5 and it has a monoclinic crystal system...
and gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
.
The total mass of the Tharsis bulge is approximately 1021 kg, about the same as the dwarf planet
Dwarf planet
A dwarf planet, as defined by the International Astronomical Union , is a celestial body orbiting the Sun that is massive enough to be spherical as a result of its own gravity but has not cleared its neighboring region of planetesimals and is not a satellite...
Ceres
CERES
CERES may refer to:* California Environmental Resources Evaluation System * Centre for European, Russian, and Eurasian Studies of the University of Toronto...
. Tharsis is so large and massive that it has likely affected the planet's moment of inertia
Moment of inertia
In classical mechanics, moment of inertia, also called mass moment of inertia, rotational inertia, polar moment of inertia of mass, or the angular mass, is a measure of an object's resistance to changes to its rotation. It is the inertia of a rotating body with respect to its rotation...
, possibly causing a change in the orientation of the planet's crust with respect to its rotational axis over time. According to one recent study, Tharsis originally formed at about 50°N latitude and migrated toward the equator between 4.2 and 3.9 billion years ago. Such shifts, known as true polar wander
True polar wander
True polar wander is a solid-body rotation of a planet or moon with respect to its spin axis, causing the geographic locations of the North and South Poles to change, or "wander". In a stable state, the largest moments of inertia axis is aligned with the spin axis, with the smaller two moment of...
, would have caused dramatic climate changes over vast areas of the planet.
Is Tharsis a Giant Volcano?
Spacecraft exploration over the last two decades has shown that volcanoes on other planets can take many unexpected forms. Over the same time period, geologists were discovering that volcanoes on Earth are more structurally complex and dynamic than previously thought. Recent work has attempted to refine the definition of a volcanoVolcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
to incorporate geologic features of widely different shapes, sizes, and compositions throughout the Solar System.One surprising and controversial conclusion from this synthesis of ideas is that the Tharsis region may be a single giant volcano. This is the thesis of geologists Andrea Borgia and John Murray in a Geological Society of America
Geological Society of America
The Geological Society of America is a nonprofit organization dedicated to the advancement of the geosciences. The society was founded in New York in 1888 by Alexander Winchell, John J. Stevenson, Charles H. Hitchcock, John R. Proctor and Edward Orton and has been headquartered at 3300 Penrose...
special paper published in 2010.
The key to understanding how a vast igneous province like Tharsis can itself be a volcano is to re-think the notion of volcano from one of simple conical edifice to that of an environment or "holistic" system. According to the conventional view in geology, volcanoes passively build up from lava and ash erupted above fissures or rifts in the crust. The rifts are produced through regional tectonic forces operating in the crust and underlying mantle. Traditionally, the volcano and its magmatic plumbing have been studied by volcanologists and igneous petrologists
Petrology
Petrology is the branch of geology that studies rocks, and the conditions in which rocks form....
, while the tectonic features are the subject for structural geologists
Structural geology
Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation in the rocks, and...
and geophysicists
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
. However, recent work on large terrestrial volcanoes indicates that the distinction between volcanic and tectonic
Tectonics
Tectonics is a field of study within geology concerned generally with the structures within the lithosphere of the Earth and particularly with the forces and movements that have operated in a region to create these structures.Tectonics is concerned with the orogenies and tectonic development of...
processes is quite blurry, with significant interplay between the two.
Many volcanoes produce deformational structures
Structural geology
Structural geology is the study of the three-dimensional distribution of rock units with respect to their deformational histories. The primary goal of structural geology is to use measurements of present-day rock geometries to uncover information about the history of deformation in the rocks, and...
as they grow. The flanks of volcanoes commonly exhibit shallow gravity slumps, faults and associated folds
Fold (geology)
The term fold is used in geology when one or a stack of originally flat and planar surfaces, such as sedimentary strata, are bent or curved as a result of permanent deformation. Synsedimentary folds are those due to slumping of sedimentary material before it is lithified. Folds in rocks vary in...
. Large volcanoes grow not only by adding erupted material to their flanks, but also by spreading laterally at their bases, particularly if they rest on weak or ductile materials. As a volcano grows in size and weight, the stress field underneath the volcano changes from compressional to extensional. A subterranean rift may develop at the base of the volcano where the crust is wrenched apart. This volcanic spreading may initiate further structural deformation in the form of thrust fault
Thrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
s along the volcano's distal flanks, pervasive graben
Graben
In geology, a graben is a depressed block of land bordered by parallel faults. Graben is German for ditch. Graben is used for both the singular and plural....
s and normal faults across the edifice, and catastrophic flank failure (sector collapse). Mathematical analysis shows that volcanic spreading operates on volcanoes at a wide range of scales and is theoretically similar to the larger-scale rifting that occurs at mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...
s (divergent plate boundaries
Divergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which produce rift valleys...
). Thus, in this view, the distinction between tectonic plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
, spreading volcano, and rift is nebulous, all being part of the same geodynamic system.
According to Borgia and Murray, Mt. Etna in Sicily
Sicily
Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...
is a good terrestrial analogue
Analogical models
Analogical models are a method of representing a phenomenon of the world, often called the ‘target system’ by another, more understandable or analysable system. They are also called dynamical analogies.- Explanation :...
for the much larger Tharsis bulge, which to them is one immense volcano they call Tharsis Rise. Mt. Etna is a complex spreading volcano that is characterized by three main structural features: a volcanic rift system that crosses the summit in a north-northeast direction; a peripheral compression belt (thrust front) surrounding the base of the volcano; and a east-northeast trending system of transtensional (oblique normal) faults that connect the summit rift to the peripheral thrust front. The volcano's peak contains an array of steep summit cones, which are frequently active. The entire edifice is also peppered with a large number of small parasitic cones.
The structural similarities of Etna to Tharsis Rise are striking, even though the latter is some 200 times larger. In Borgia and Murray's view, Tharsis resembles a very large spreading volcano. As with Etna, the spreading has produced a rift through the summit of the rise and a system of radial tear faults that connect the rift to a basal compression belt. The tear-fault system on Tharsis is represented by the radial fossae, of which Valles Marineris
Valles Marineris
Valles Marineris is a system of canyons that runs along the Martian surface east of the Tharsis region...
is the largest example. The thrust front is visible as the Thaumasia Highlands. Unlike on Earth, where the rifting of plates produces a corresponding subduction zone, the thick lithosphere of Mars is unable to descend into the mantle. Instead, the compressed zone is scrunched up and sheared laterally into mountain ranges, in a process called obduction
Obduction
Obduction is the overthrusting of continental crust by oceanic crust or mantle rocks at a convergent plate boundary. It can occur during an orogeny, or mountain-building episode....
. To complete the analogy, the huge Olympus Mons and the Tharsis Montes are merely summit cones or parasitic cones on a much larger volcanic edifice.
Tharsis in popular culture
- In Kim Stanley RobinsonKim Stanley RobinsonKim Stanley Robinson is an American science fiction writer known for his award-winning Mars trilogy. His work delves into ecological and sociological themes regularly, and many of his novels appear to be the direct result of his own scientific fascinations, such as the fifteen years of research...
's Mars trilogyMars trilogyThe Mars trilogy is a series of award-winning science fiction novels by Kim Stanley Robinson that chronicles the settlement and terraforming of the planet Mars through the intensely personal and detailed viewpoints of a wide variety of characters spanning almost two centuries...
, two major cities called Cairo and Nicosia are located in this region, as well as many mentions of Noctis Labyrinthus and the surrounding areas. - In the game Killzone 2 Tharsis is a mining region on the planet Helghast.
- Tharsis appears in the Japanese manga and anime Voices of a Distant StarVoices of a Distant Staris a Japanese anime OVA by Makoto Shinkai. It chronicles a long-distance relationship between two close friends who communicate by sending emails via their mobile phones across interstellar space...
, where the first encounter between mankind and an alien race referred to as Tarsians took place. - In the anime Cowboy BebopCowboy Bebopis a critically acclaimed and award-winning 1998 Japanese anime series directed by Shinichirō Watanabe, written by Keiko Nobumoto, and produced by Sunrise. Its 26 episodes comprise a complete storyline: set in 2071, the series follows the adventures, misadventures and tragedies of five bounty...
, Vicious is stationed with the Red Dragon Syndicate in the region. - The Tharsis plateau is the setting of the Warhammer 40,000Warhammer 40,000Warhammer 40,000 is a tabletop miniature wargame produced by Games Workshop, set in a dystopian science fantasy universe. Warhammer 40,000 was created by Rick Priestley in 1987 as the futuristic companion to Warhammer Fantasy Battle, sharing many game mechanics...
novel Mechanicum by Graham McNeill. - In Sealab 2021Sealab 2021Sealab 2021 is an American animated television series. It was shown on Cartoon Network's adult-oriented programming block, Adult Swim. It premiered on November 23, 2000 and the final episode aired on April 25, 2005...
episode "Der Dieb", Captain Murphy makes references to the Tharsian region on Mars: "Then as of this moment, I am hereby married to Adrienne BarbeauAdrienne BarbeauAdrienne Jo Barbeau is an American actress and the author of three books. Barbeau came to prominence in the 1970s as Broadway's original Rizzo in the musical Grease, and as Carol Traynor, the divorced daughter of Maude Findlay in the sitcom Maude...
, queen of Mars from Olympus Mons to Tharsis" - The video game Red Faction: GuerrillaRed Faction: GuerrillaRed Faction: Guerrilla is an open-world third-person action video game developed by Volition, Inc. and published by THQ. It was released for the PlayStation 3 and Xbox 360 in June 2009 and for Microsoft Windows in September 2009...
takes place entirely in the Tharsis region. Also in the game, it is proposed that the infamous Ultor Corporation's mining complex was also in Tharsis. - In the novel SpinSpin (novel)Spin is a science fiction novel by author Robert Charles Wilson. It was published in 2005 and won the Hugo Award for Best Novel in 2006. It is the first book in the Spin trilogy, with Axis published in 2007 and Vortex published in July 2011.-Plot:Set in the near future, Spin begins with the sudden...
by Robert Charles WilsonRobert Charles WilsonRobert Charles Wilson is an American-Canadian science fiction author.Wilson was born in the United States in California, but grew up near Toronto, Ontario. Apart from another short period in the early 1970s spent in Whittier, California, he has lived most of his life in Canada, and in 2007 he...
, the return trip to Earth is launched from Tharsis after 100,000 years since Martian colonization, but before Mars is enveloped by the spin.