Outflow channels
Encyclopedia
Outflow channels is the term used to describe extremely long, wide swathes of scoured ground on Mars
, commonly containing the streamlined remnants of pre-existing topography and other linear erosive features indicating sculpting by fluids moving downslope. Channels extend many hundreds of kilometers in length and are typically greater than one kilometer in width; the largest valley (Kasei Vallis
) is around 3500 km long, greater than 400 km wide and exceeds 2.5 km in depth cut into the surrounding plains. These features tend to appear fully sized at fractures in the Martian surface, either from chaos terrain
s or from canyon systems or other tectonically controlled, deep graben
, though there are exceptions. Besides their exceptional size, the channels are also characterized by low sinuosities
and high width:depth ratios compared both to other Martian valley features and to terrestrial river channels. Crater counts
indicate that most of the channels were cut since the early Hesperian
, though the age of the features is variable between different regions of Mars. Some outflow channels in the Amazonis
and Elysium Planitia
e regions have yielded ages of only tens of million years, extremely young by the standards of Martian topographic features.
On the basis of their geomorphology, locations and sources, the channels are today generally thought to have been carved by outburst floods (huge, rare, episodic floods of liquid water
), although some authors still make the case for formation by the action of glacier
s, lava
, or debris flows. Calculations indicate that the volumes of water required to cut such channels at least equal and most likely exceed by several orders of magnitude the present discharges of the largest terrestrial rivers, and are probably comparable to the largest floods known to have ever occurred on Earth (e.g., those that cut the Channeled Scablands
in North America or those released during the re-flooding of the Mediterranean basin at the end of the Messinian Salinity Crisis
). Such exceptional flow rates and the implied associated volumes of water released could not be sourced by precipitation but rather demand the release of water from some long-term store, probably a subsurface aquifer sealed by ice and subsequently breached by meteorite impact or igneous activity.
The outflow channels contrast with the Martian channel features known as "valley networks
", which much more closely resemble the dendritic planform more typical of terrestrial river drainage basin
s.
Outflow channels tend to be named after the names for Mars in various ancient world languages, or more rarely for major terrestrial rivers.
is a roughly circular volcanic plain west of the Tharsis
bulge and its associated volcanic systems. This region contains the most prominent and numerous outflow channels on Mars. The channels flow east or north into the plain.
and Elysium
from the southern highlands, or originate at graben within the plains. This region contains some of the youngest channels. Some of these channels have rare tributaries, and they do not start at Chaos. It has been suggested the formation mechanisms for these channels may be more variable than for those around Chryse Planitia, perhaps in some cases involving lake breaches at the surface.
volcanic province and flow northwestward to the Utopia Planitia
. As common in the Amazonis and Elysium Planitiae regions, these channels tend to originate in graben. Some of these channels may be influenced by lahars, as indicated by their surface textures and ridged, lobate deposits at their margins and termini. The valleys of Hephaestus Fossae and Hebrus Valles are of extremely unusual form, and although sometimes claimed as outflow channels, are of enigmatic origin.
basin.
, Ladon
, Margaritifer and Ares
Valles, although now separated by large craters, once comprised a single outflow channel flowing north into Chryse Planitia
. The source of this outflow has been suggested as overflow from the Argyre
crater, formerly filled to the brim as a lake
by channels (Surius, Dzigai, and Palacopus Valles) draining down from the south pole. If real, the full length of this drainage system would be over 8000 km, the longest known drainage path in the solar system. Under this suggestion, the extant form of the outflow channel Ares Vallis would thus be a remolding of a pre-existing structure.
and Chasma Australe, have both been argued to have been formed by meltwater release from beneath polar ice, as in a terrestrial jökulhlaup
. However, others have argued for an eolian origin, with them induced by katabatic winds blowing down from the poles.
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...
, commonly containing the streamlined remnants of pre-existing topography and other linear erosive features indicating sculpting by fluids moving downslope. Channels extend many hundreds of kilometers in length and are typically greater than one kilometer in width; the largest valley (Kasei Vallis
Kasei Vallis
Kasei Vallis, which means "Mars" in Japanese, is a large channel system in the Lunae Palus quadrangle, on Mars. It is located at 24.6° north latitude and 65° west longitude. It begins in Echus Chasma, near Valles Marineris, and empties into Chryse Planitia, not far from where Viking 1 landed. Kasei...
) is around 3500 km long, greater than 400 km wide and exceeds 2.5 km in depth cut into the surrounding plains. These features tend to appear fully sized at fractures in the Martian surface, either from chaos terrain
Chaos terrain
Chaos terrain is an astrogeological term used to denote planetary surface areas where features such as ridges, cracks, and plains appear jumbled and enmeshed with one another. Chaos terrain is a notable feature of the planet Mars and Jupiter's moon Europa...
s or from canyon systems or other tectonically controlled, deep 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....
, though there are exceptions. Besides their exceptional size, the channels are also characterized by low sinuosities
Sinuosity
Sinuosity or sinuosity index is a measure of deviation of a path between two points from the shortest possible path...
and high width:depth ratios compared both to other Martian valley features and to terrestrial river channels. Crater counts
Crater counting
Crater counting is a method for estimating the age of a planet's surface. The method is based upon the assumptions that a new surface forms with zero impact craters, and that impact craters accumulate at some constant rate...
indicate that most of the channels were cut since the early Hesperian
Hesperian
The Hesperian is a geologic system and time period on the planet Mars characterized by widespread volcanic activity and catastrophic flooding that carved immense outflow channels across the surface. The Hesperian is an intermediate and transitional period of Martian history...
, though the age of the features is variable between different regions of Mars. Some outflow channels in the Amazonis
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...
and Elysium Planitia
Elysium Planitia
Elysium Planitia is the second largest volcanic region on Mars, after Tharsis Montes. It is centered at . It includes volcanoes, from north to south, Hecates Tholus, Elysium Mons and Albor Tholus. Another large volcano, Apollinaris Mons, lies south of the others. Besides having large volcanoes,...
e regions have yielded ages of only tens of million years, extremely young by the standards of Martian topographic features.
On the basis of their geomorphology, locations and sources, the channels are today generally thought to have been carved by outburst floods (huge, rare, episodic floods of liquid water
Water on Mars
Water on Mars is a psychedelic rock and electronic music group from Quebec City, Québec, Canada. The music trio is led by Philippe Navarro, guitarist, vocalist, arranger, producer, principal lyricist, and music composer....
), although some authors still make the case for formation by the action of glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s, 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...
, or debris flows. Calculations indicate that the volumes of water required to cut such channels at least equal and most likely exceed by several orders of magnitude the present discharges of the largest terrestrial rivers, and are probably comparable to the largest floods known to have ever occurred on Earth (e.g., those that cut the Channeled Scablands
Channeled scablands
The Channeled Scablands are a unique geological erosion feature in the U.S. state of Washington. They were created by the cataclysmic Missoula Floods that swept periodically across eastern Washington and down the Columbia River Plateau during the Pleistocene epoch. Geologist J Harlen Bretz coined...
in North America or those released during the re-flooding of the Mediterranean basin at the end of the Messinian Salinity Crisis
Messinian salinity crisis
The Messinian Salinity Crisis, also referred to as the Messinian Event, and in its latest stage as the Lago Mare event, was a geological event during which the Mediterranean Sea went into a cycle of partly or nearly complete desiccation throughout the latter part of the Messinian age of the Miocene...
). Such exceptional flow rates and the implied associated volumes of water released could not be sourced by precipitation but rather demand the release of water from some long-term store, probably a subsurface aquifer sealed by ice and subsequently breached by meteorite impact or igneous activity.
The outflow channels contrast with the Martian channel features known as "valley networks
Valley networks (Mars)
Valley networks are branching networks of valleys on Mars that superficially resemble terrestrial river drainage basins. They are found mainly incised into the terrain of the martian southern highlands, and are typically - though not always - of Noachian age...
", which much more closely resemble the dendritic planform more typical of terrestrial river drainage basin
Drainage basin
A drainage basin is an extent or an area of land where surface water from rain and melting snow or ice converges to a single point, usually the exit of the basin, where the waters join another waterbody, such as a river, lake, reservoir, estuary, wetland, sea, or ocean...
s.
Outflow channels tend to be named after the names for Mars in various ancient world languages, or more rarely for major terrestrial rivers.
List of outflow channels by region
This is a partial list of named channel structures on Mars claimed as outflow channels in the literature, largely following The Surface of Mars by Carr. The channels tend to cluster in certain regions on the Martian surface, often associated with volcanic provinces, and the list reflects this. Originating structures at the head of the channels, if clear and named, are noted in parentheses and in italics after each entry.Circum-Chryse region
Chryse PlanitiaChryse 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...
is a roughly circular volcanic plain west of the Tharsis
Tharsis
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 volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as...
bulge and its associated volcanic systems. This region contains the most prominent and numerous outflow channels on Mars. The channels flow east or north into the plain.
- Ares VallisAres VallisAres Vallis is an outflow channel on Mars, named after the Greek name for Mars: Ares, the god of war; it appears to have been carved by fluids, perhaps water...
(Aram ChaosAram ChaosAram Chaos, centered at 2.6°N, 21.5°W, comprises a heavily eroded impact crater on the planet Mars. It lies at the eastern end of the large canyon Valles Marineris and close to Ares Vallis. Various geological processes have reduced it to a circular area of chaotic terrain...
; Iani ChaosIani ChaosIani Chaos, the source region of Ares Vallis on Mars, is centered at ~342°E, 2°S. The chaotic terrain is widely believed to have formed via the removal of subsurface water or ice, resulting in flooding at the surface, and the formation of Ares Vallis...
) - Ganges ChasmaGanges ChasmaThe Ganges Chasma is a deep canyon at the eastern end of the vast Valles Marineris system on Mars, an offshoot of Eos Chasma. It is named after the River Ganges in South Asia. It has been tentatively identified as an outflow channel....
? - Kasei VallisKasei VallisKasei Vallis, which means "Mars" in Japanese, is a large channel system in the Lunae Palus quadrangle, on Mars. It is located at 24.6° north latitude and 65° west longitude. It begins in Echus Chasma, near Valles Marineris, and empties into Chryse Planitia, not far from where Viking 1 landed. Kasei...
(Echus ChasmaEchus ChasmaEchus 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:...
; Hebes ChasmaHebes ChasmaHebes Chasma is an isolated chasma just north of the Valles Marineris canyon system of Mars. It is centered at 1 degree southern latitude and 76 degrees western longitude, just between the Martian equator and the Valles Marineris system, just east of the Tharsis region.-Geography:Hebes Chasma is a...
) - Maja VallesMaja VallesMaja Valles is a large, ancient outflow channel in the Lunae Palus quadrangle on Mars. Its location is 12.6° north latitude and 58.3° west longitude. The name is a Nepali word for "Mars". Maja Valles begins at Juventae Chasma. Parts of the system have been partially buried by thin volcanic debris...
(Juventae ChasmaJuventae ChasmaJuventae Chasma is an enormous box canyon on Mars which opens to the north and forms the outflow channel Maja Valles....
) - Mawrth VallisMawrth VallisMawrth Vallis is a valley on Mars at 22.3°N, 343.5°E with an elevation approximately two kilometres below datum. It is an ancient water outflow channel with light-colored clay-rich rocks.Mawrth Vallis is one of the oldest valleys on Mars...
(no obvious source) - Ravi VallisRavi VallisRavi Vallis is an ancient outflow channel in the Margaritifer Sinus quadrangle on Mars, located at 0.2° S and 40.7 W°. It is 205.5 km long and was named after the Ravi River, an ancient Pakistani River....
(nameless rubble-filled depression) - Shalbatana VallisShalbatana VallisShalbatana Vallis is an ancient water-worn channel on Mars, located in the Oxia Palus quadrangle at 7.8° north latitude and 42.1° west longitude. It is the westernmost of the southern Chryse outflow channels...
(chaos in Orson Welles crater; Ganges ChasmaGanges ChasmaThe Ganges Chasma is a deep canyon at the eastern end of the vast Valles Marineris system on Mars, an offshoot of Eos Chasma. It is named after the River Ganges in South Asia. It has been tentatively identified as an outflow channel....
?) - Simud VallesSimud VallesSimud Valles is an ancient outflow channel in the Oxia Palus quadrangle of Mars, located at 19.8° N and 37.8° W. It is 945.0 km long and was named for the word for "Mars" in Sumerian. Note: Descriptor term changed to the plural , and coordinates redefined 3/31/2008....
(Hydraotes ChaosHydraotes ChaosHydraotes Chaos is a broken up region in the Oxia Palus quadrangle of Mars, located at 0.8° North and 35.4° West. It is 417.5 km across and was named after a classical albedo feature name. More information and more examples of Chaos can be found at Chaos terrain....
; Aureum ChaosAureum ChaosAureum Chaos is a rough, collapsed region in the Margaritifer Sinus quadrangle of Mars at4.4° south latitude and 27° west longitude. It is 368 km across and was named after a classical albedo feature name...
?; Arsinoes Chaos?) - Tiu VallesTiu VallesTiu Valles is an outflow channel in the Oxia Palus quadrangle of Mars, located at 15.9° North and 35.7° West.It is 1,720 km long and was named after the word for "Mars" in old English ....
(Aram ChaosAram ChaosAram Chaos, centered at 2.6°N, 21.5°W, comprises a heavily eroded impact crater on the planet Mars. It lies at the eastern end of the large canyon Valles Marineris and close to Ares Vallis. Various geological processes have reduced it to a circular area of chaotic terrain...
?; Aureum Chaos?)
Tharsis region
In this region it is particularly difficult to distinguish outflow channels from lava channels but the following features have been suggested as at least overprinted by outflow channel floods:- Parts of the Olympica FossaeOlympica FossaeOlympica Fossae is a trough in the Tharsis quadrangle of Mars at25° north latitude and 114.1° west longitude. It is about 420 km long and was named after an albedo feature at 17N, 134W...
- Valleys adjacent to the southeast margin of Olympus MonsOlympus MonsOlympus 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...
(nameless graben)
Amazonis and Elysium Planitiae
Several channels flow either onto the plains of AmazonisAmazonis 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...
and Elysium
Elysium Planitia
Elysium Planitia is the second largest volcanic region on Mars, after Tharsis Montes. It is centered at . It includes volcanoes, from north to south, Hecates Tholus, Elysium Mons and Albor Tholus. Another large volcano, Apollinaris Mons, lies south of the others. Besides having large volcanoes,...
from the southern highlands, or originate at graben within the plains. This region contains some of the youngest channels. Some of these channels have rare tributaries, and they do not start at Chaos. It has been suggested the formation mechanisms for these channels may be more variable than for those around Chryse Planitia, perhaps in some cases involving lake breaches at the surface.
- Al-Qahira Vallis
- Athabasca Vallis (Cerberus FossaeCerberus FossaeThe Cerberus Fossae are a series of semi-parallel fissures on Mars formed by faults which pulled the crust apart in the Cerberus region . Ripples seen at the bottom of the fault are sand blown by the wind ....
) - Grjota Vallis (nameless graben)
- Ma'adim VallisMa'adim VallisMa'adim Vallis is one of the largest outflow channels on Mars, about 700 km long and significantly larger than Earth's Grand Canyon. It is over 20 km wide and 2 km deep in some places. It runs from a region of southern lowlands thought to have once contained a large group of lakes ...
(shallow depression in Highlands) - Mangala Vallis (nameless graben)
- Marte VallisMarte VallisMarte Vallis is a valley in the Amazonis quadrangle of Mars, located at 15 North and 176.5 West. It is 185 km long and was named for the Spanish word for "Mars"...
(Cerberus Planitia)
Utopia Planitia
Several outflow channels rise in the region west of the ElysiumElysium Mons
Elysium Mons is a volcano on Mars located in the Elysium Planitia, at , in the Martian eastern hemisphere. It stands about 13.9 km above the surrounding lava plains, and about 16 km above the Martian datum. Its diameter is about 240 km, with a summit caldera about 14 km across...
volcanic province and flow northwestward to the Utopia Planitia
Utopia Planitia
Utopia Planitia is the largest recognized impact basin on Mars with an estimated diameter of 3300 km, and is the Martian region where the Viking 2 lander touched down and began exploring on September 3, 1976. It is located at the antipode of Argyre Planitia, centered at...
. As common in the Amazonis and Elysium Planitiae regions, these channels tend to originate in graben. Some of these channels may be influenced by lahars, as indicated by their surface textures and ridged, lobate deposits at their margins and termini. The valleys of Hephaestus Fossae and Hebrus Valles are of extremely unusual form, and although sometimes claimed as outflow channels, are of enigmatic origin.
- Granicus VallisGranicus VallisGranicus Vallis is a valley in the Amenthes quadrangle of Mars, located at 30° north latitude and 229° west longitude. It is 750 km long and is named after the ancient name for river in Turkey. It has been identified as an outflow channel....
(graben radial to Elysium MonsElysium MonsElysium Mons is a volcano on Mars located in the Elysium Planitia, at , in the Martian eastern hemisphere. It stands about 13.9 km above the surrounding lava plains, and about 16 km above the Martian datum. Its diameter is about 240 km, with a summit caldera about 14 km across...
) - Hrad VallesHrad VallesHrad Valles is an ancient outflow channel in the Cebrenia quadrangle of Mars, located at 38.7° north latitude and 224.7° west longitude. It is 825 km in length and was named for the word for "Mars" in Armenian.- Volcano ice interactions :...
(graben radial to Elysium Mons) - Tinjar VallisTinjar VallisTinjar Vallis is an ancient outflow channel in the Amenthes quadrangle of Mars, located at 38° north latitude and 235.8° west longitude. It is 425 km long and was named after a modern river in Sarawak, Malaysia....
(graben radial to Elysium Mons) - Hebrus VallesHebrus VallesHebrus Valles is an ancient system of troughs and valleys in the Amenthes quadrangle of Mars, located at 20.2° north latitude and 233.4° west longitude. It is 317 km long and was named after an ancient river in Greece...
(irregular depression; ends in discontinuous linear hollows) - Hephaestus FossaeHephaestus FossaeHephaestus Fossae is a system of troughs and channels in the Cebrenia quadrangle of Mars, with a location centered at 21.1 N and 237.5 W. It is 604 km long and was named after a classical albedo feature name. The Fossae have been tentatively identified as outflow channels, but their origin...
(irregular depression; flows through angular segments; ends in discontinuous linear hollows)
Hellas region
Three valleys flow from east of its rim down onto the floor of the HellasHellas Planitia
Hellas Planitia, also known as the Hellas Impact Basin, is a huge, roughly circular impact basin located in the southern hemisphere of the planet Mars. It is the second or third largest impact crater and the largest visible impact crater known in the Solar System...
basin.
- Dao VallisDao VallisDao Vallis is a valley on Mars that appears to have been carved by water. It runs southwestward into Hellas Planitia, and has been identified as an outflow channel. It and its tributary, Niger Vallis, extend for about 1200 km. It is named after the Thai word for star...
(box canyonBox canyonBox Canyon is a Box canyon in Ouray County, Colorado, United States. It was originally founded as a mining camp and helped the city of Ouray establish itself as a permanent community. Box Canyon is home to Box Canyon Falls, a 285-foot waterfall, with quartzite walls that extend almost one hundred...
near Hadriaca Patera) - Harmakhis VallisHarmakhis VallisHarmakhis Vallis is a valley near Hellas Planitia, Mars. It has been identified as an outflow channel, the site of catastrophic floods of water during Mars' past.Gullies are also common on the wall of Harmakhis Vallis, as seen the image below...
(close to end of Reull VallisReull VallisReull Vallis is a valley on Mars that appears to have been carved by water. It runs westward into the Channels of Reull Vallis which runs north westwards into Hellas Planitia. It is named after the Gaelic word for planet.- Lineated Floor Deposits :...
) - Niger VallisNiger VallisNiger Vallis is a valley on Mars that appears to have been carved by water. It has been identified as an outflow channel. It merges with Dao Vallis which runs southwestward into Hellas Planitia from the volcanic Hadriacus Mons. Like Dao, it was formed around the Late Noachian and Early Hesperian...
(indistinct depressions near Hadriaca Patera)
Argyre region
It has been argued that UzboiUzboi Vallis
Uzboi Vallis is a valley on Mars. It is named after a dry river valley in USSR, now in Turkmenistan.The valley begins on the northern rim of the Argyre basin, and cuts through several craters, before ending at Holden crater....
, Ladon
Ladon Valles
Ladon Valles is a river valley on the planet of Mars in the Margaritifer Sinus quadrangle located at 22.6° South and 28.7° West. It is 278 km long and was named after an ancient name for a Greek river...
, Margaritifer and Ares
Ares Vallis
Ares Vallis is an outflow channel on Mars, named after the Greek name for Mars: Ares, the god of war; it appears to have been carved by fluids, perhaps water...
Valles, although now separated by large craters, once comprised a single outflow channel flowing north into 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...
. The source of this outflow has been suggested as overflow from the Argyre
Argyre
In Greek and Roman mythology, Argyre was a mythical island of silver, located in the east. The name comes from the Greek argyros ....
crater, formerly filled to the brim as a lake
Lake
A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...
by channels (Surius, Dzigai, and Palacopus Valles) draining down from the south pole. If real, the full length of this drainage system would be over 8000 km, the longest known drainage path in the solar system. Under this suggestion, the extant form of the outflow channel Ares Vallis would thus be a remolding of a pre-existing structure.
Polar regions
The large troughs present in each pole, Chasma BorealeChasma Boreale
Chasma Boreale is a large canyon in the Mare Boreum quadrangle of Mars at 83° north latitude and 47.1° west longitude. It is about long and was named after a classical albedo feature name. The canyon shows layered features that result from seasonal melting and deposition of ice, together with...
and Chasma Australe, have both been argued to have been formed by meltwater release from beneath polar ice, as in a terrestrial jökulhlaup
Jökulhlaup
A jökulhlaup is a glacial outburst flood. It is an Icelandic term that has been adopted by the English language. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland which are triggered by geothermal heating and occasionally by a volcanic subglacial...
. However, others have argued for an eolian origin, with them induced by katabatic winds blowing down from the poles.