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{{Short description|Volcanic plateau on Mars}}
{{About|the volcanic plateau on Mars}}
{{Infobox feature on celestial object
|name = Tharsis rise
|image = Tharsis - Valles Marineris MOLA shaded colorized zoom 32.jpg
|caption = The Tharsis region (shown in shades of red and brown) dominates the western hemisphere of Mars as seen in this [[Mars Orbiter Laser Altimeter]] (MOLA) colorized relief map.
|type = Volcanic plateau, volcanic province
|eponym = [[Tarshish]]
|diameter = ~5 000 km<ref name=Carr />
|peak = ~7 km (excluding volcanoes)<ref name=Boyce />
|coordinates = {{coord|0|00|N|260|00|E|globe:mars_type:landmark|display=inline,title}}
|coordinates_footnotes = <ref name=gpn>{{gpn|5947|Tharsis}} (Center Latitude: 0.00°, Center Longitude: 260.00°)</ref>
|location = Eastern hemisphere of [[Mars]]
}}

'''Tharsis''' ({{IPAc-en|'|θ|ɑːr|s|ᵻ|s}}) is a vast [[volcanic plateau]] centered near the equator in the western hemisphere of [[Mars]].{{refn| Officially, "Tharsis" is an albedo feature.<ref name = "USGS_Tharsis">{{cite web
 | title = Tharsis
 | work = Gazetteer of Planetary Nomenclature
 | publisher = [[USGS Astrogeology Science Center]] 
 | url = https://planetarynames.wr.usgs.gov/Feature/5947
 | access-date = 2013-11-29}}</ref>| group = note}} 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 the western extremity of the known world.<ref>{{cite web |url=http://pds.jpl.nasa.gov/planets/welcome/glossary.htm |title=Welcome to the Planets Version 1.5 |publisher=pds.jpl.nasa.gov}}</ref>

==Location and size==
[[File:PIA02035 Map of Mars' Topography.jpg|thumb|upright=1.4|Global topography of Mars based on [[Mars Orbiter Laser Altimeter|MOLA]] data. The '''Tharsis bulge''' is the large area at left (shown in shades of red and white). [[Amazonis Planitia|Amazonis]] and [[Chryse Planitia|Chryse]] Planitiae are the blue areas left (west) and right (east) of Tharsis, respectively. In this image, the higher average elevation of the southern hemisphere (zonal spherical harmonic degree 1) has been removed to highlight the elevation contrast of Tharsis with the rest of the planet.]]
Tharsis can have many meanings depending on historical and scientific context. The name is commonly used in a broad sense to represent a [[continent]]-sized region of anomalously elevated terrain centered just south of the equator around longitude 265°E.<ref name=Carr>Carr, M.H. (2006). ''The Surface of Mars;'' Cambridge University Press: Cambridge, UK, p. 46. {{ISBN|978-0-521-87201-0}}.</ref>  Called the '''Tharsis bulge''' or Tharsis rise, this broad, elevated region dominates the western hemisphere of Mars and is the largest [[topography|topographic]] feature on the planet, after the [[Martian dichotomy|global dichotomy]].<ref name=Boyce>Boyce, J.M. (2008). ''The Smithsonian Book of Mars; ''Konecky & Konecky: Old Saybrook, CT, p. 101. {{ISBN|1-56852-714-4}}.</ref>

Tharsis has no formally defined boundaries,<ref>Morton, O. (2002). ''Mapping Mars: Science, Imagination, and the Birth of a World;'' Picador: New York, p. 98, {{ISBN|0-312-42261-X}}.</ref> so precise dimensions for the region are difficult to give. In general, the bulge is about {{convert|5000|km|mi}} across<ref name=Carr /> and up to {{convert|7|km|mi}} high<ref name=Boyce /> (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 Mons]] (about 55°N) to the southern base of the [[Thaumasia quadrangle|Thaumasia]] highlands (about 43°S). Depending on how the region is defined, Tharsis covers {{convert|10|–|30|e6km2|e6sqmi|sigfig=1|abbr=off}}, or up to 25% of Mars's surface area.<ref>Tanaka, K.L.; Scott, D.H.; Greeley, R. (1992). Global Stratigraphy in ''Mars,'' H.H. Kieffer et al., Eds; University of Arizona Press: Tucson, AZ, p. 369. {{ISBN|0-8165-1257-4}}.</ref><ref name=Williams>{{cite journal | last1 = Williams | first1 = J.-P. | last2 = Nimmo | first2 = F. | last3 = Moore | first3 = W. B. | last4 = Paige | first4 = D. A. | year = 2008 | title = The Formation of Tharsis on Mars: What the Line-of-Sight Gravity Is Telling Us. | url = https://authors.library.caltech.edu/12885/1/WILjgre08.pdf| journal = J. Geophys. Res. | volume = 113 | issue = E10| page = E10011 | doi = 10.1029/2007JE003050 | bibcode=2008JGRE..11310011W}}</ref><ref>{{cite web |last=King|first= S.D. |date=2010 |title= More Speculations on the Origin of the Tharsis Rise. 41st Lunar and Planetary Science Conference, LPI: Houston, Abstract #2007 |url= http://www.lpi.usra.edu/meetings/lpsc2010/pdf/2007.pdf }}</ref>

===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 rise 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.<ref name=Smith>{{cite journal | last1 = Smith | first1 = D.E. | display-authors = etal   | date = 1999 | title = The Global Topography of Mars and Implications for Surface Evolution | journal = Science | volume = 284 | issue = 5419| pages = 1495–1503 | doi=10.1126/science.284.5419.1495 | pmid=10348732|bibcode = 1999Sci...284.1495S }}</ref><ref>Boyce, J.M. (2008). ''The Smithsonian Book of Mars; ''Konecky & Konecky: Old Saybrook, CT, p. 103. {{ISBN|1-56852-714-4}}.</ref> The northern rise partially overlies sparsely cratered, lowland plains north of the [[Martian dichotomy|dichotomy]] boundary. This region is dominated by [[Alba Mons]] and its extensive volcanic flows. Alba Mons is a vast, low-lying volcanic construct that is unique to Mars. Alba Mons is so large and topographically distinct that it can almost be treated as an entire volcanic province unto itself.<ref>{{cite web |author=Banerdt W.B. |author2=Golombek, M.P. |date=2000 |title= Tectonics of the Tharsis Region of Mars: Insights from MGS Topography and Gravity. 31st Lunar and Planetary Science Conference; LPI: Houston, TX, Abstract #2038 |url=http://www.lpi.usra.edu/meetings/lpsc2000/pdf/2038.pdf |publisher=lpi.usra.edu}}</ref><ref>{{cite book |last=Frankel |first=C. |date=2005 |title=Worlds on Fire: Volcanoes on the Earth, the Moon, Mars, Venus and Io |publisher=[[Cambridge University Press]] |location=Cambridge, UK |page=[https://archive.org/details/worldsonfirevolc00fran/page/134 134] |isbn=978-0-521-80393-9 |url=https://archive.org/details/worldsonfirevolc00fran/page/134 }}</ref> The oldest part of the northern rise consists of a broad topographic ridge that corresponds to the highly fractured terrain of [[Ceraunius Fossae]].<ref>{{cite journal | last1 = Ivanov | first1 = M. A. | last2 = Head | first2 = J.W. | year = 2006 | title = Alba Patera, Mars: Topography, Structure, and Evolution of a Unique Late Hesperian–Early Amazonian Shield Volcano | journal = J. Geophys. Res. | volume = 111 | issue = E9| page = E09003 | doi = 10.1029/2005JE002469 | bibcode=2006JGRE..111.9003I| doi-access = free }}</ref>  The ridge is oriented north–south and forms part of the Noachian-aged basement on which Alba Mons 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.<ref name=Scott>Scott, D.H.; Tanaka, K.L. (1986). Geologic Map of the Western Equatorial Region of Mars. USGS; I-1802-A.</ref> 
[[File:Syria-Thaumasia.jpg|thumb|right|upright=1.4|[[Mars Orbiter Laser Altimeter|MOLA]] topography of the Thaumasia Plateau (Syria-Thaumasia block) and southern Tharsis. The volcano shown at the left is [[Arsia Mons]]. [[Valles Marineris]] extends across the northern edge. The areas in brown have the highest elevations on the Tharsis Plateau and may be considered the "summit region" of the Tharsis bulge.]]
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 quadrangle|Memnonia]] and [[Terra Sirenum]] regions. To the east, the southern Tharsis bulge consists of the [[Thaumasia Plateau]], an extensive stretch of volcanic plains about 3,000&nbsp;km wide.<ref>Carr, M.H. (2006). ''The Surface of Mars;'' Cambridge University Press: Cambridge, UK, p. 92-93. {{ISBN|978-0-521-87201-0}}.</ref> The [[Thaumasia Plateau]] is bounded to the west by a highly elevated zone of fractures ([[Claritas Fossae]]) and mountains (the Thaumasia Highlands<ref>{{cite journal | last1 = Dohm | first1 = J.M. | last2 = Tanaka | first2 = K.L. | date = 1999 | title = Geology of the Thaumasia Region, Mars: Plateau Development, Valley Origins, and Magmatic Evolution | journal = Planet. Space Sci. | volume = 36 | issue = 3–4 | pages = 411–431 | doi=10.1016/s0032-0633(98)00141-x|bibcode = 1999P&SS...47..411D | url = https://zenodo.org/record/1259697 }}</ref>) that curves south then east to northeast in a wide arc that has been compared to the shape of a scorpion's tail.<ref name=Smith /><ref>{{cite web |author=Williams, J-.P. |author2= Moore, W.B. |author3= Nimmo, F. |date=2004 |title=The Formation of Tharsis in the Early Noachian: What the Line-of-Sight Gravity is Telling Us. Second Conference on Early Mars, LPI: Houston, Abstract #8054 |url=http://www.lpi.usra.edu/meetings/earlymars2004/pdf/8054.pdf }}</ref> The plateau province 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.<ref>{{cite web |author=Saunders, R.S. |author2=Roth, L.E. |author3=Downs, G.S. |date=1980 |title= Pre-Tharsis Martian Tectonism and Volcanism: Evidence from the Coprates Region. 11th Lunar and Planetary Science Conference; LPI: Houston, TX, Abstract #1348 |url= http://www.lpi.usra.edu/meetings/lpsc1980/pdf/1348.pdf }}</ref> These boundaries enclose a broad high plateau and shallow interior basin that include [[Syria Planum|Syria]], Sinai, and Solis Plana (see [[list of plains on Mars]]). The highest plateau elevations  on the Tharsis bulge 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{{by whom|date=November 2022}} 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.<ref name=Scott />  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 up to {{convert|200|km|mi}} wide. These northwestern slope valleys (NSVs) - which [[debouch]] into [[Amazonis Planitia]] - are separated by a parallel set of gigantic "keel-shaped" promontories. The NSVs may be relics from catastrophic floods of water, similar to the huge outflow channels that empty into Chryse Planitia, east of Tharsis.<ref>{{cite journal | last1 = Dohm | first1 = J.M. | display-authors = etal   | date = 2004 | title = System of Gigantic Valleys Northwest of Tharsis, Mars' Latent Catastrophic Flooding, Northwest Watershed, and Implications for Northern Plains Ocean | journal = Geophys. Res. Lett. | volume = 27 | issue = 21| pages = 3559–3562 | doi=10.1029/2000gl011728 | bibcode=2000GeoRL..27.3559D| doi-access = free }}</ref> Central Tharsis is approximately {{convert|3500|km|mi}} 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.

[[Olympus Mons]] and its associated lava flows and aureole deposits form another distinct subprovince of the Tharsis region. This subregion is about {{convert|1600|km|mi}} across. It lies off the main topographic bulge, but is related to the volcanic processes that formed Tharsis.<ref name=Smith /> 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 [[volcanism]] and associated [[tectonic]] processes that have caused extensive crustal deformation. According to the standard view, Tharsis overlies a [[hotspot (geology)|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]]<ref>Dohm, J.M. ''et al.'' (2007). Traits and Evolution of the Tharsis Superplume, Mars in ''Superplumes: Beyond Plate Tectonics,'' D.A. Yuen et al., Eds.; Springer, pp. 523–536, {{ISBN|978-1-4020-5749-6}}.</ref>) 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.
[[File:Tharsis-PIA02049.jpg|thumb|[[Orographic lift|Orographic]] water ice clouds hover over the volcanic peaks of the central Tharsis region in this color image mosaic from [[Mars Global Surveyor]]. [[Olympus Mons]] dominates at upper left.  At center are the three [[Tharsis Montes]]: [[Arsia Mons]] at bottom, [[Pavonis Mons]] at center, and [[Ascraeus Mons]] at top.]]
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 rock|intrusive]] complexes ([[pluton]]s). If the magma migrates through vertical fractures it produces swarms of [[dike (geology)|dikes]] that may be expressed at the surface as long, linear cracks ([[fossa (geology)|fossa]]e) and [[crater chain]]s (catenae). Magma may also intrude the crust horizontally as large tabular bodies, such as [[sill (geology)|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.<ref>{{cite journal | last1 = Williams | first1 = J.-P. | last2 = Paige | first2 = D.A. | last3 = Manning | first3 = C.E. | year = 2003 | title = Layering in the Wall Rock of Valles Marineris: Intrusive and Extrusive Magmatism | journal = Geophys. Res. Lett. | volume = 30 | issue = 12| page = 1623 | doi = 10.1029/2003GL017662 | bibcode=2003GeoRL..30.1623W| s2cid = 949559 }}</ref>

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.<ref>Boyce, J.M. (2008). ''The Smithsonian Book of Mars; ''Konecky & Konecky: Old Saybrook, CT, p. 107. {{ISBN|1-56852-714-4}}.</ref><ref>{{cite journal | last1 = Solomon | first1 = S.C. | last2 = Head | first2 = J.W. | year = 1982 | title = Evolution of the Tharsis Province of Mars: The Importance of Heterogeneous Lithospheric Thickness and Volcanic Construction | journal = J. Geophys. Res. | volume = 87 | issue = B12| pages = 9755–9774 | doi=10.1029/jb087ib12p09755 | bibcode=1982JGR....87.9755S| citeseerx = 10.1.1.544.5865 }}</ref> The enormous sagging weight of Tharsis has generated tremendous stresses in the crust, producing a broad trough around the region<ref name=Phillips>{{cite journal | last1 = Phillips | first1 = R.J. | display-authors = etal   | date = 2001 | title = Ancient Geodynamics and Global-Scale Hydrology on Mars | journal = Science | volume = 291 | issue = 5513 | pages = 2587–2591 | doi=10.1126/science.1058701 | pmid=11283367|bibcode = 2001Sci...291.2587P | s2cid = 36779757 }}</ref> and an array of radial fractures emanating from the center of the bulge that stretches halfway across the planet.<ref>Carr, M.H (2007). Mars: Surface and Interior in ''Encyclopedia of the Solar System,'' 2nd ed., McFadden, L.-A. et al. Eds. Elsevier: San Diego, CA, p.319</ref>

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,<ref name=Phillips /> some 3.7 billion years ago.<ref>{{cite journal | last1 = Carr | first1 = M.H. | last2 = Head | first2 = J.W. | date = 2010 | title = Geologic History of Mars | journal = Earth Planet. Sci. Lett. | volume = 294 | issue = 3–4 | page = 186 | doi=10.1016/j.epsl.2009.06.042| bibcode = 2010E&PSL.294..185C | url = https://zenodo.org/record/1258929 }}</ref> 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.<ref>{{cite journal | last1 = Solomon | first1 = S.C. | display-authors = etal   | year = 2005 | title = New Perspectives on Ancient Mars | journal = Science | volume = 307 | issue = 5713| pages = 1214–1220 | doi = 10.1126/science.1101812 | pmid=15731435|bibcode = 2005Sci...307.1214S | hdl = 2060/20040191823 | s2cid = 27695591 | hdl-access = free }}</ref>
 
By one estimate, the Tharsis bulge contains around 300 million km<sup>3</sup> of igneous material. Assuming the magma that formed Tharsis contained [[carbon dioxide]] (CO<sub>2</sub>) 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 CO<sub>2</sub> atmosphere and a global layer of water 120 m thick.<ref name=Phillips /> 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<ref>{{Cite journal|author3-link=John F. Mustard|last1=Bibring|first1=Jean-Pierre|date=2006|title=Global Mineralogical and Aqueous Mars History Derived from OMEGA/Mars Express Data|journal=Science|volume=312|issue=5772|pages=400–404|doi=10.1126/science.1122659|pmid=16627738|last2=Langevin|first2=Y|last3=Mustard|first3=JF|last4=Poulet|first4=F|author5-link=Raymond Arvidson|last5=Arvidson|first5=R|last6=Gendrin|first6=A|last7=Gondet|first7=B|last8=Mangold|first8=N|last9=Pinet|first9=P |last10=Forget|first10=F|last11=Berthé|first11=M|last12=Bibring|first12=J. P.|last13=Gendrin|first13=A|last14=Gomez|first14=C|last15=Gondet|first15=B|last16=Jouglet|first16=D|last17=Poulet|first17=F|last18=Soufflot|first18=A|last19=Vincendon|first19=M|last20=Combes|first20=M|last21=Drossart|first21=P|last22=Encrenaz|first22=T|last23=Fouchet|first23=T|last24=Merchiorri|first24=R|last25=Belluci|first25=G|last26=Altieri|first26=F|last27=Formisano|first27=V|last28=Capaccioni|first28=F|last29=Cerroni|first29=P|last30=Coradini|first30=A|bibcode = 2006Sci...312..400B |display-authors=8|doi-access=free}}</ref>) when [[sulfuric acid]] [[weathering]] produced abundant hydrated sulfate minerals such as [[kieserite]] and [[gypsum]].

Two [[European Space Agency]] (ESA) probes have discovered [[Frost|water frost]] deposits on Tharsis during the morning. Previously, it was thought that water frost on the equator Mars was impossible.<ref>{{Cite web |date=2025-04-07 |title=In a significant first, researchers detect water frost on solar system's tallest volcanoes {{!}} Brown University |url=https://www.brown.edu/news/2024-06-10/mars-frost |access-date=2025-04-11 |website=www.brown.edu |language=en}}</ref> Such findings are significant to understanding the present day [[water cycle]] on Mars and its [[Life on Mars|habitability]].<ref>{{Cite web |last=Carter |first=Jamie |title=Scientists Make 'Impossible' Discovery On Mars—Frost Near The Equator |url=https://www.forbes.com/sites/jamiecartereurope/2024/06/11/mars-impossible-discovery-as-frost-found-near-equator/ |access-date=2024-06-27 |website=Forbes |language=en}}</ref>

==True polar wander on Mars==
{{Main|True polar wander on Mars}}

The total mass of the Tharsis bulge is approximately 10<sup>21</sup> kg,<ref>A volume of 3 x 10<sup>8</sup> km<sup>3</sup> (Phillips et al., 2001) multiplied by average density of the igneous material (3.1 x 10<sup>3</sup> kg/m<sup>3</sup>) times conversion factor of 1 x 10<sup>9</sup> m<sup>3</sup>/km<sup>3</sup> gives a mass of 9.3 x 10<sup>20</sup> (or ~10<sup>21</sup>) kg. Average density is from Nimmo and Tanaka (2005), p. 138.</ref> about the same as the [[dwarf planet]] [[Ceres (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.<ref>{{cite journal | last1 = Nimmo | first1 = F. | last2 = Tanaka | first2 = K. | date = 2005 | title = Early Crustal Evolution of Mars | journal = Annu. Rev. Earth Planet. Sci. | volume = 33 | pages = 133–161 | doi=10.1146/annurev.earth.33.092203.122637 | bibcode=2005AREPS..33..133N}}</ref> According to one recent study,<ref>{{cite journal | last1 = Arkani-Hamed | first1 = J | year = 2009 | title = Polar Wander of Mars: Evidence from Giant Impact Basins | journal = Icarus | volume = 204 | issue = 2| pages = 489–498 | doi =10.1016/j.icarus.2009.07.020 | bibcode = 2009Icar..204..489A }}</ref> 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.  A more recent study reported in Nature agreed with the polar wander, but the authors thought the eruptions at Tharsis happened at a slightly different time.<ref>{{cite journal | last1 = Bouley | first1 = S. | last2 = Baratoux | first2 = D. | last3 = Matsuyama | first3 = I. | last4 = Forget | first4 = F. | last5 = Séjourné | first5 = A. | last6 = Turbet | first6 = M. | last7 = Costard | first7 = F. | year = 2016 | title = Late Tharsis formation and implications for early Mars | journal = Nature | volume =  531| issue = 7594| pages =  344–347| doi = 10.1038/nature17171 | pmid = 26934230 | bibcode = 2016Natur.531..344B | s2cid = 4464498 }}</ref>

==Volcanism==
[[File:Clouds over lava flows on Mars ESA384876.jpg|thumb|Images of ice water clouds over Tharsis taken by the [[ExoMars Trace Gas Orbiter]], 2016]]
Spacecraft exploration over the last two decades has shown that volcanoes on other planets can take many unexpected forms.<ref>For specific examples, see [[Corona (planetary geology)|coronae]] and [[arachnoid (astrogeology)|arachnoids]] on the planet [[Venus]] or [[cryovolcano]]es in the outer Solar System.</ref> Over the same time period, geologists were discovering that volcanoes on Earth are more structurally complex and dynamic than previously thought.<ref>{{cite journal | last1 = Borgia | first1 = A. | last2 = Delaney | first2 = P.T. | last3 = Denlinger | first3 = P.T. | date = 2000 | title = Spreading Volcanoes | journal = Annu. Rev. Earth Planet. Sci. | volume = 28 | pages = 539–70 | doi=10.1146/annurev.earth.28.1.539|bibcode = 2000AREPS..28..539B }}</ref> Recent work has attempted to refine the definition of a [[volcano]] to incorporate geologic features of widely different shapes, sizes, and compositions throughout the Solar System.<ref>{{cite book |title=What Is a Volcano? |editor= Edgardo Cañón-Tapia |editor2= Alexandru Szakács |journal=Geological Society of America |volume= 470 |issue=Special Paper 470|date= 2010|pages=v–vii| doi=10.1130/2010.2470(00) |series= Geological Society of America Special Papers |isbn= 978-0-8137-2470-6 }}</ref> One surprising and controversial conclusion from this synthesis of ideas is that the Tharsis region may be a single giant volcano.<ref>{{cite web |last=Fazekas |first=A. |title= New Biggest Volcano in the Solar System? |publisher=National Geographic News |date=December 3, 2010 |url=http://news.nationalgeographic.com/news/2010/12/101203-science-space-biggest-volcano-solar-system-mars/|archive-url=https://web.archive.org/web/20101204235420/http://news.nationalgeographic.com/news/2010/12/101203-science-space-biggest-volcano-solar-system-mars/|url-status=dead|archive-date=December 4, 2010}}</ref> This is the thesis of geologists Andrea Borgia and John Murray in a [[Geological Society of America]] special paper published in 2010.<ref>Borgia, A.; Murray, J. (2010). Is Tharsis Rise, Mars, a Spreading Volcano? in ''What Is a Volcano?,'' E. Cañón-Tapia and A. Szakács, Eds.; Geological Society of America Special Paper 470, 115–122, {{doi|10.1130/2010.2470(08)}}.</ref>

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 [[rift (geology)|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 [[petrology|petrologists]], while the tectonic features are the subject for [[structural geology|structural geologists]] and [[geophysics|geophysicists]]. However, recent work on large terrestrial volcanoes indicates that the distinction between volcanic and [[tectonics|tectonic]] processes is quite blurry, with significant interplay between the two.

Many volcanoes produce deformational [[structural geology|structures]] as they grow. The flanks of volcanoes commonly exhibit shallow gravity slumps, [[fault (geology)|fault]]s and associated [[fold (geology)|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 (mechanics)|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.<ref>Borgia, A. (1994). Dynamic Basis of Volcanic Spreading. ''J. Geophys. Res.'' '''99'''(B4), pp. 17,791-17,804.</ref> This volcanic spreading may initiate further structural deformation in the form of [[thrust fault]]s along the volcano's [[Anatomical terms of location#Proximal and distal|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 boundary|divergent plate boundaries]]). Thus, in this view, the distinction between [[plate tectonics|tectonic plate]], spreading volcano, and rift is nebulous, all being part of the same geodynamic system.

According to Borgia and Murray, [[Mount Etna]] in [[Sicily]] is a good terrestrial [[Analogical models|analogue]] for the much larger Tharsis bulge, which to them is one immense volcano they call Tharsis Rise. Mount 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 an east-northeast trending system of transtensional (oblique normal) faults that connect the summit rift to the peripheral thrust front.<ref>Borgia, A.; Murray, J. (2010). Is Tharsis Rise, Mars, a Spreading Volcano? in ''What Is a Volcano?,'' E. Cañón-Tapia and A. Szakács, Eds.; Geological Society of America Special Paper 470, p. 120, {{doi|10.1130/2010.2470(08)}}.</ref> 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.<ref>Frankel, C. (2005). ''Worlds on Fire: Volcanoes on the Earth, the Moon, Mars, Venus and Io;'' Cambridge University Press: Cambridge, UK, p. 48. {{ISBN|978-0-521-80393-9}}.</ref>

The structural similarities of Mount 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 fault]]s that connect the rift to a basal compression belt. The tear-fault system on Tharsis is represented by the radial [[fossa (geology)|fossa]]e, 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.

==Tharsis in popular culture==
* In the [[Dragonlance]] Chronicles, the City of Tarsis is a port town which has become landlocked after the Cataclysm led to the recession of the sea. Its waterfront district was located on the west side of the city.
* In [[Kim Stanley Robinson]]'s [[Mars trilogy]], three major cities—Cairo, Sheffield, and Nicosia—are located in this region, as well as many mentions of Noctis Labyrinthus and the surrounding areas.
*Tharsis appears in the 2002 Japanese manga and anime ''[[Voices of a Distant Star]]'', where the first encounter took place between mankind and an alien race referred to as Tarsians.
*In the anime ''[[Cowboy Bebop]]'', the headquarters of the Red Dragon Syndicate is in Tharsis City.
*The Tharsis plateau is a main setting of the [[The Horus Heresy (novels)|Horus Heresy]] novel [[Horus Heresy (novels)#book9|''Mechanicum'']] by [[Graham McNeill]], Book 9 of the ''Horus Heresy'' book series. The book includes a story-related map of the region (by [[Book illustration|illustrator]] Adrian Wood) in its [[front matter]].<ref>{{cite book|last=McNeill|first=Graham|date=2008|title=Mechanicum: war comes to Mars|type=print|others=Cover art & illustration by Neil Roberts; map by Adrian Wood|series=Horus Heresy {{interp|book series}}|volume=9|publisher=[[Black Library]]|location=[[Nottingham, UK]]|edition=1st UK|at={{interp|Map:}} "The Tharsis Quadrangle of Mars" {{interp|pp.&nbsp;8–9 (not numbered)}}|isbn=978-1-84416-664-0|author-link=Graham McNeill}}</ref> 
*In the "Der Dieb" episode of ''[[Sealab 2021]]'', Captain Murphy proclaims that "[...] as of this moment, I am hereby married to [[Adrienne Barbeau]], queen of Mars from Olympus Mons to Tharsis."
*The [[video game]] ''[[Red Faction: Guerrilla]]'' takes place entirely in the Tharsis region, and implies that the infamous Ultor Corporation's mining complex in [[Red Faction (video game)|the first game]] had also been in Tharsis.
*In the 2005 novel [[Spin (novel)|''Spin'']] by [[Robert Charles Wilson]], the return trip to Earth is launched from Tharsis after 100,000 years since Martian colonization, but before Mars is enveloped by the spin.
*In the game ''[[Myth II: Soulblighter]]'', Tharsis is the name of a volcano that features heavily in the final level.
*Tharsis is the name of an [[Tharsis (video game)|independent game on Steam]] based on a mission to the region. However, it does not involve landing there.
*The [[video game]] ''[[Destiny (video game)|Destiny]]'' has a reference to Tharsis in one of their locations named Tharsis Junction.
*One of the Kataphrakts of the anime ''[[Aldnoah.Zero]]'' is named ''Tharsis''. Its original pilot is part of an organization that serves an empire based on the planet of Mars.
*The "Battle of Tharsis Bulge" is part of the backstory of the [[Revelation Space series|Revelation Space]] series by [[Alastair Reynolds]], and is referenced several times by the Conjoiners.
*In [[Natasha Pulley]]'s novel ''The Mars House'' (published 19 March 2024), Tharsis is the name of a terraformed Mars colony.<ref>{{Cite web |title=The Mars House |url=https://store.gollancz.co.uk/products/the-mars-house |access-date=2023-12-14 |website=Gollancz |language=en}}</ref>

==See also==
* [[Geography of Mars]]
* [[Geology of Mars]]
* [[Volcanism on Mars]]

== Explanatory notes ==
{{reflist|group=note}}

==References==
{{Reflist|colwidth=30em}}

==External links==
* [http://svs.gsfc.nasa.gov/vis/a000000/a000600/a000654/ NASA image and animation of the Tharsis region in true color] {{Webarchive|url=https://web.archive.org/web/20201022100509/http://svs.gsfc.nasa.gov/vis/a000000/a000600/a000654/ |date=2020-10-22 }}
* [http://record.wustl.edu/archive/2001/03-30-01/articles/mars.html Researchers pinpoint region responsible for Mars' heyday]

{{Geography of Mars|cartography}}
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[[Category:Mountains on Mars]]
[[Category:Surface features of Mars]]
[[Category:Volcanoes of Mars]]
[[Category:Lava plateaus]]
[[Category:Extraterrestrial plateaus]]