Enipeus Vallis is a valley in the northern hemisphere of the planet

Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...

. It is centered at lat. 37°N, long. 267°E in the

Arcadia quadrangle The Arcadia quadrangle is one of a series of 30 quadrangle maps of Mars used by the United States Geological Survey (USGS) Astrogeology Research Program. The quadrangle is located in the north-central portion of Mars’ western hemisphere and ...

(MC-3) between the large volcano

Alba Mons Alba Mons (formerly and still occasionally known as Alba Patera, a term that has since been restricted to the volcano's summit caldera; also initially known as the Arcadia ring) is a volcano located in the northern Tharsis region of the planet Ma ...

and the

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. ...

plateau. The valley follows a gently

sinuous Sinuosity, sinuosity index, or sinuosity coefficient of a continuously differentiable curve having at least one inflection point is the ratio of the curvilinear length (along the curve) and the Euclidean distance (straight line) between the ...

, north-south path for a distance of about 357 km (222 mi).USGS Gazetteer of Planetary Nomenclature. http://planetarynames.wr.usgs.gov/Feature/1803. It is likely an ancient

watercourse A stream is a continuous body of surface water flowing within the bed and banks of a channel. Depending on its location or certain characteristics, a stream may be referred to by a variety of local or regional names. Long large streams are ...

that formed during the early

Hesperian The Hesperian is a system (stratigraphy), geologic system and geologic timescale, time period on the planet Mars characterized by widespread Volcanology of Mars, volcanic activity and catastrophic flooding that carved immense outflow channels acr ...

(or late

Noachian The Noachian is a geologic system and early time period on the planet Mars characterized by high rates of meteorite and asteroid impacts and the possible presence of abundant surface water. The absolute age of the Noachian period is uncerta ...

) period,Moore, H.J. (2001). Geologic Map of the Tempe-Mareotis Region of Mars. USGS Geologic Investigations Series I-2727. http://geopubs.wr.usgs.gov/i-map/i2727/. around 3.7 billion years ago. The valley is named after a river in

Thessaly Thessaly ( el, Θεσσαλία, translit=Thessalía, ; ancient Thessalian: , ) is a traditional geographic and modern administrative region of Greece, comprising most of the ancient region of the same name. Before the Greek Dark Ages, Thes ...

Greece Greece,, or , romanized: ', officially the Hellenic Republic, is a country in Southeast Europe. It is situated on the southern tip of the Balkans, and is located at the crossroads of Europe, Asia, and Africa. Greece shares land borders with ...

. Enipeus is also the name of a river god in

classical mythology Classical mythology, Greco-Roman mythology, or Greek and Roman mythology is both the body of and the study of myths from the ancient Greeks and ancient Romans as they are used or transformed by cultural reception. Along with philosophy and polit ...

. The

International Astronomical Union The International Astronomical Union (IAU; french: link=yes, Union astronomique internationale, UAI) is a nongovernmental organisation with the objective of advancing astronomy in all aspects, including promoting astronomical research, outreac ...

(IAU) formally adopted the name Enipeus Vallis in 1991. ''Vallis'' is the Latin word for valley.

General description

Enipeus Vallis is mapped as a valley network. Valley networks are branching systems of valleys on Mars that superficially resemble terrestrial river

drainage basin A drainage basin is an area of land where all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, t ...

s. They are abundant in the equatorial and southern highlands of the planet but less common in the northern hemisphere. Most valley networks are thought to have formed by flowing water, although the primary source of the water (melting ice, rainfall, springs) is still debated.Carr, M.H. (2006). ''The Surface of Mars''; Cambridge University Press: Cambridge, UK, p. 113. . Enipeus Vallis is a single trunk valley, with no large tributaries. The valley is widest (about ) at its southernmost reach near Lat. 33.6°N and rapidly tapers northward, maintaining a regular width of throughout most of its course. Above lat. 39.7°N the valley opens up, and drainage features become poorly integrated and ill-defined. North of this area, a somewhat subdued valley segment continues to the northwest from 40.5°N to about 42.5°N (northwest of the crater Lowbury) where it is locally buried by impact crater ejecta and young ( Amazonian-aged) plains material. This northern valley segment gradually loses its identity amid the narrow

graben In geology, a graben () is a depressed block of the crust of a planet or moon, bordered by parallel normal faults. Etymology ''Graben'' is a loan word from German, meaning 'ditch' or 'trench'. The word was first used in the geologic contex ...

s of

Tantalus Fossae Tantalus Fossae is a group of troughs in the Arcadia quadrangle of Mars, located at 50.9° north latitude and 97.5° west longitude. They are about 2,400 km long and was named after an albedo feature at 35N, 110W. Troughs like this one a ...

. The elevation of the valley floor ranges from above

datum In the pursuit of knowledge, data (; ) is a collection of discrete values that convey information, describing quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted. ...

( Mars "sea" level) in the south to or less in the north, where the northern segment of the valley begins to lose its definition. In cross-sectional profile, the valley is

U-shaped Many shapes have metaphorical names, i.e., their names are metaphors: these shapes are named after a most common object that has it. For example, "U-shape" is a shape that resembles the letter U, a bell-shaped curve has the shape of the vertical ...

to rectangular, with depths ranging from .JMARS gridded MOLA elevation dataset. In the south, Enipeus Vallis has

levee A levee (), dike (American English), dyke (English in the Commonwealth of Nations, Commonwealth English), embankment, floodbank, or stop bank is a structure that is usually soil, earthen and that often runs parallel (geometry), parallel to ...

-like ridges along its edges that are up to high. The levees are locally breached by lava flows from the surrounding plains. In places, inner channels are visible along the valley floor. At around 36°N, the channels form an

anastomosing An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal ...

(braided) pattern. Near the middle section of the southern valley segment, the valley divides into several branches, which then rejoin to form diamond-shaped islands. Faint longitudinal

striations Striations means a series of ridges, furrows or linear marks, and is used in several ways: * Glacial striation * Striation (fatigue), in material * Striation (geology), a ''striation'' as a result of a geological fault * Striation Valley, in ...

and streamlined erosional

bedform A bedform is a geological feature that develops at the interface of fluid and a moveable Bed (geology), bed, the result of bed material being moved by fluid flow. Examples include Current ripples, ripples and dunes on the Stream bed, bed of a riv ...

s are common all along the floor of the valley. (See Photo Gallery.) In

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

geomorphology Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or n ...

, a distinction is made between the terms stream valley and

stream channel In physical geography, a channel is a type of landform consisting of the outline of a path of relatively shallow and narrow body of water or of other fluids (e.g., lava), most commonly the confine of a river, river delta or strait. The word is c ...

. Stream valleys are wide, elongate depressions. The stream itself flows within the confines of a channel in the center of the valley. A stream valley usually contains many channels. Channels are always much narrower and shallower than the valley that contains them, and water in the stream channel never comes close to filling the entire valley.Carr, M.H. (1996). ''Water on Mars;'' Oxford, p. 47. . The distinction is important when discussing features of probable fluvial origin on Mars. Although Enipeus Vallis is described here as a valley, it has many features typical of a channel, including fluvial bedforms, streamlined features, a U-shaped profile,Baker, V.R.; Carr, M.H.; Gulick, V.C.; Williams, C.R.; Marley, M.S. (1992). "Channels and Valley Networks" in ''Mars,'' H.H. Kieffer et al. Eds.; University of Arizona Press: Tucson, 493–522. and levee deposits, which are always associated with channels not valleys. Except for its small width and general

sinuosity Sinuosity, sinuosity index, or sinuosity coefficient of a continuously differentiable curve having at least one inflection point is the ratio of the curvilinear length (along the curve) and the Euclidean distance (straight line) between the e ...

, Enipeus Vallis has characteristics resembling the immense Martian

outflow channels Outflow channels are extremely long, wide swathes of scoured ground on Mars. They extend many hundreds of kilometers in length and are typically greater than one kilometer in width. They are thought to have been carved by huge outburst floods. ...

, which are true channels formed by the catastrophic release of large volumes of water. Fluvial landforms like Enipeus Vallis that show characteristics of both valley networks and outflow channels are relatively common on Mars ( Ma'adim Vallis, for example). and indicate that fluvial erosion on Mars has a distinctive genesis and evolution compared to Earth.

Regional geology

Enipeus Vallis is located at the western edge of the

plateau in the Tempe-Mareotis region. The region lies on a broad

topographic Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary scie ...

shelf bounded by the higher elevations of Alba Mons to the west and Tempe Terra to the east. The region slopes gently to the north with a gradient of 0.3° or less. The area is characterized by abundant lava flows, low volcanic

shields A shield is a piece of personal armour held in the hand, which may or may not be strapped to the wrist or forearm. Shields are used to intercept specific attacks, whether from close-ranged weaponry or projectiles such as arrows, by means of a ...

, and small domes that are part of the Tempe Volcanic Province, a northeastern extension of the

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 (plural ''montes'') is the Latin word for mountain; it is a ...

chain of volcanoes. Although spatially related to the large Tharsis volcanoes, volcanism in the Tempe Volcanic Province has a different eruptive style and has been likened to the

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

ic plains volcanism seen in

Idaho Idaho ( ) is a state in the Pacific Northwest region of the Western United States. To the north, it shares a small portion of the Canada–United States border with the province of British Columbia. It borders the states of Montana and Wyom ...

’s

Snake River Plain image:Snake River view near Twin Falls, Idaho.jpg, The Snake River cutting through the plain leaves many canyons and Canyon#List of gorges, gorges, such as this one near Twin Falls, Idaho The Snake River Plain is a geology, geologic feature ...

.Plescia, J.B. (1981). The Tempe Volcanic Province of Mars and Comparisons with the Snake River Plains of Idaho. ''Icarus,'' 45, 586–601. This category of volcanic activity is intermediate between flood (plateau) basalts and Hawaiian volcanism.Moore, H.J. (1995). Geology of the Tempe-Mareotis Region, Mars. 26th Lunar and Planetary Science Conference, Abstract #1497. http://www.lpi.usra.edu/meetings/lpsc1995/pdf/1497.pdf.Greeley, R. (1982). The Snake River Plain, Idaho: Representative of a New Category of Volcanism. ''J. Geophys. Res.,'' 87(B4), 2705-2712, http://www.agu.org/pubs/crossref/1982/JB087iB04p02705.shtml. The region is transected by numerous northeast-trending

s that form parts of the Tempe,

Mareotis Lake Mariout ( ar, بحيرة مريوط ', , also spelled Maryut or Mariut), is a brackish lake in northern Egypt near the city of Alexandria. The lake area covered and had a navigable canal at the beginning of the 20th century, but at the begin ...

, and

; these are fracture systems of varying ages that are oriented radially from the

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

bulge. The region west of Enipeus Vallis is characterized by Hesperian-aged volcanic flows from

. The area to the east consists of fractured and terraced highland plateaus of

age. At the end of the Noachian period, these highland materials underwent an episode of

erosion and resurfacing. Enipeus Vallis probably formed during this fluvial episode.

Photo gallery

Image:Southern Enipeus Vallis.jpg, Southern end of Enipeus Vallis is about 10 km wide and broadly U-shaped in profile. The western wall of the valley has a straight NE orientation similar to that of fractures in the Noachian plateau materials to the east. This suggests that the valley formed along pre-existing faults. (

THEMIS In Greek mythology and Ancient Greek religion, religion, Themis (; grc, Θέμις, Themis, justice, law, custom) is one of the twelve Titans, Titan children of Gaia and Uranus (mythology), Uranus, and the second wife of Zeus. She is the godde ...

VIS image) Image:Enipeus Vallis.JPG,

Anastomosing An anastomosis (, plural anastomoses) is a connection or opening between two things (especially cavities or passages) that are normally diverging or branching, such as between blood vessels, leaf veins, or streams. Such a connection may be normal ...

channels in Enipeus Vallis at 35.9°N, 267.0E, as seen in

HiRISE High Resolution Imaging Science Experiment is a camera on board the ''Mars Reconnaissance Orbiter'' which has been orbiting and studying Mars since 2006. The 65 kg (143 lb), US$40 million instrument was built under the direction o ...

image. Image:Enipeus Central Channel V29345011.jpg, Enipeus Vallis (right). Note inner channel, levee-like deposits, and streamlined bedforms. (

VIS image) Image:Enipeus anabranches.jpg, Middle portion of Enipeus Vallis. The valley divides into several channels, forming large central island at 37.0°N, 267.2°E. Image is

VIS mosaic.

Notes

References

*JMARS. http://jmars.asu.edu/. (See Christensen, P.; Gorelick, N.; Anwar, S.; Dickenshied, S.; Edwards, C.; Engle, E. (2007) "New Insights About Mars From the Creation and Analysis of Mars Global Datasets;" American Geophysical Union, Fall Meeting, abstract #P11E-01. http://adsabs.harvard.edu/abs/2007AGUFM.P11E..01C.)

General description

Regional geology

Photo gallery

Notes

References

See also