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71-600: Olympus Mons is the youngest of the large volcanoes on Mars, having formed during the Martian Hesperian Period with eruptions continuing well into the Amazonian Period . It has been known to astronomers since the late 19th century as the albedo feature Nix Olympica (Latin for "Olympic Snow"), and its mountainous nature was suspected well before space probes confirmed it as a mountain. Two impact craters on Olympus Mons have been assigned provisional names by

142-422: A central trough of molten, flowing lava. Partially collapsed lava tubes are visible as chains of pit craters, and broad lava fans formed by lava emerging from intact, subsurface tubes are also common. In places along the volcano's base, solidified lava flows can be seen spilling out into the surrounding plains, forming broad aprons, and burying the basal escarpment. Crater counts from high-resolution images taken by

213-457: A depth of about 32 km (105,000 ft) below the caldera floor. Crater size-frequency distributions on the caldera floors indicate the calderas range in age from 350 Mya to about 150 Mya. All probably formed within 100 million years of each other. It is possible that the magma chambers within Olympus Mons received new magma from the mantle after the caldera floors formed, leading to

284-477: A discrete stratum bound above or below by adjacent units (illustrated right). Using principles such as superpositioning (illustrated left), cross-cutting relationships , and the relationship of impact crater density to age, geologists can place the units into a relative age sequence from oldest to youngest. Units of similar age are grouped globally into larger, time-stratigraphic ( chronostratigraphic ) units, called systems . For Mars, four systems are defined:

355-399: A disk of gas around a condensed central object, such as, for example, a protostar, one can derive a disk scale height which is somewhat analogous to the planetary scale height. We start with a disc of gas that has a mass which is small relative to the central object. We assume that the disc is in hydrostatic equilibrium with the z component of gravity from the star, where the gravity component

426-491: A feature unique among the shield volcanoes of Mars, which may have been created by enormous flank landslides . Olympus Mons covers an area of about 300,000 km (120,000 sq mi), which is approximately the size of Italy or the Philippines , and it is supported by a 70 km (43 mi) thick lithosphere . The extraordinary size of Olympus Mons is likely because Mars lacks mobile tectonic plates . Unlike on Earth,

497-436: A geologic period represents the time interval over which the strata of a system were deposited, including any unknown amounts of time present in gaps. Periods are measured in years, determined by radioactive dating . On Mars, radiometric ages are not available except from Martian meteorites whose provenance and stratigraphic context are unknown. Instead, absolute ages on Mars are determined by impact crater density, which

568-470: A given altitude is a result of the weight of the overlying atmosphere. If at a height of z the atmosphere has density ρ and pressure P , then moving upwards an infinitesimally small height dz will decrease the pressure by amount dP , equal to the weight of a layer of atmosphere of thickness  dz . Thus: d P d z = − g ρ {\displaystyle {\frac {dP}{dz}}=-g\rho } where g

639-582: A given system are apt to contain gaps ( unconformities ) analogous to missing pages from a book. In some places, rocks from the system are absent entirely due to nondeposition or later erosion. For example, rocks of the Cretaceous System are absent throughout much of the eastern central interior of the United States. However, the time interval of the Cretaceous (Cretaceous Period) still occurred there. Thus,

710-954: A non-perfectly conducting disk is rotating through a poloidal magnetic field (i.e., the initial magnetic field is perpendicular to the plane of the disk), then a toroidal (i.e., parallel to the disk plane) magnetic field will be produced within the disk, which will pinch and compress the disk. In this case, the gas density of the disk is: ρ ( r , z ) = ρ 0 ( r ) exp ⁡ ( − ( z h D ) 2 ) − ρ cut ( r ) [ 1 − exp ⁡ ( − ( z h D ) 2 ) ] {\displaystyle \rho (r,z)=\rho _{0}(r)\exp \left(-\left({\frac {z}{h_{D}}}\right)^{2}\right)-\rho _{\text{cut}}(r)\left[1-\exp \left(-\left({\frac {z}{h_{D}}}\right)^{2}\right)\right]} where

781-429: A number of wrinkle ridges located at the basal escarpment. Why opposite sides of the mountain should show different styles of deformation may lie in how large shield volcanoes grow laterally and in how variations within the volcanic substrate have affected the mountain's final shape. Large shield volcanoes grow not only by adding material to their flanks as erupted lava, but also by spreading laterally at their bases. As

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852-869: A rock outcrop in the Upper Ordovician Series of the Ordovician System. You could even collect a fossil trilobite there. However, you could not visit the Late Ordovician Epoch in the Ordovician Period and collect an actual trilobite. The Earth-based scheme of rigid stratigraphic nomenclature has been successfully applied to Mars for several decades now but has numerous flaws. The scheme will no doubt become refined or replaced as more and better data become available. (See mineralogical timeline below as example of alternative.) Obtaining radiometric ages on samples from identified surface units

923-417: A volcano grows in size, the stress field underneath the volcano changes from compressional to extensional. A subterranean rift may develop at the base of the volcano, causing the underlying crust to spread apart. If the volcano rests on sediments containing mechanically weak layers (e.g., beds of water-saturated clay), detachment zones ( décollements ) may develop in the weak layers. The extensional stresses in

994-656: Is a vast, low-lying plain that covers much of the northern hemisphere of Mars. It is generally interpreted to consist of reworked sediments originating from the Late Hesperian outflow channels and may be the remnant of an ocean that covered the northern lowland basins. Another interpretation of the Vastitas Borealis Formation is that it consists of lava flows. The Hesperian System is subdivided into two chronostratigraphic series : Lower Hesperian and Upper Hesperian. The series are based on referents or locations on

1065-475: Is about 600 km (370 mi) wide. Because the mountain is so large, with complex structure at its edges, allocating a height to it is difficult. Olympus Mons stands 21 km (13 mi) above the Mars global datum , and its local relief, from the foot of the cliffs which form its northwest margin to its peak, is over 21 km (13 mi) (a little over twice the height of Mauna Kea as measured from its base on

1136-485: Is an idealized stratigraphic column based on the physical rock record of a type area (type section) correlated with rocks sections from many different locations planetwide. A system is bound above and below by strata with distinctly different characteristics (on Earth, usually index fossils ) that indicate dramatic (often abrupt) changes in the dominant fauna or environmental conditions. (See Cretaceous–Paleogene boundary as example.) At any location, rock sections in

1207-473: Is clearly necessary for a more complete understanding of Martian chronology. The Hesperian was a time of declining rates of impact cratering, intense and widespread volcanic activity, and catastrophic flooding. Many of the major tectonic features on Mars formed at this time. The weight of the immense Tharsis Bulge stressed the crust to produce a vast network of extensional fractures ( fossae ) and compressive deformational features ( wrinkle ridges ) throughout

1278-488: Is expansive and does not drop off in density with height as sharply as Earth's. The composition of Olympus Mons is approximately 44% silicates , 17.5% iron oxides (which give the planet its red coloration), 7% aluminium , 6% magnesium , 6% calcium , and particularly high proportions of sulfur dioxide with 7%. These results point to the surface being largely composed of basalts and other mafic rocks, which would have erupted as low viscosity lava flows and hence lead to

1349-565: Is heavily dependent upon models of crater formation over time. Accordingly, the beginning and end dates for Martian periods are uncertain, especially for the Hesperian/Amazonian boundary, which may be in error by a factor of 2 or 3. The lower boundary of the Hesperian System is defined as the base of the ridged plains, which are typified by Hesperia Planum and cover about a third of the planet's surface. In eastern Hesperia Planum,

1420-532: Is much more uncertain and could range anywhere from 3200 to 2000 Mya, with 3000 Mya being frequently cited. The Hesperian Period is roughly coincident with the Earth's early Archean Eon. With the decline of heavy impacts at the end of the Noachian, volcanism became the primary geologic process on Mars, producing vast plains of flood basalts and broad volcanic constructs ( highland paterae ). By Hesperian times, all of

1491-451: Is pointing to the midplane of the disk: d P d z = − G M ∗ ρ z ( r 2 + z 2 ) 3 / 2 {\displaystyle {\frac {dP}{dz}}=-{\frac {GM_{*}\rho z}{(r^{2}+z^{2})^{3/2}}}} where: In the thin disk approximation, z ≪ r {\displaystyle z\ll r} and

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1562-708: Is the acceleration due to gravity. For small dz it is possible to assume g to be constant; the minus sign indicates that as the height increases the pressure decreases. Therefore, using the equation of state for an ideal gas of mean molecular mass M at temperature T , the density can be expressed as ρ = M P R T {\displaystyle \rho ={\frac {MP}{RT}}} Combining these equations gives d P P = − d z k B T / m g {\displaystyle {\frac {dP}{P}}={\frac {-dz}{{k_{\text{B}}T}/{mg}}}} which can then be incorporated with

1633-1021: Is the gas mass density at the midplane of the disk at a distance r from the center of the star and h D {\displaystyle h_{D}} is the disk scale height with h D = 2 k T r 3 G M ∗ m ¯ ≈ 0.0306 ( T / 100   K ) ( r / 1  au ) 3 ( M ∗ / M ⊙ ) ( m ¯ / 2  amu )    au {\displaystyle h_{D}={\sqrt {\frac {2kTr^{3}}{GM_{*}{\bar {m}}}}}\approx 0.0306{\sqrt {\frac {\left(T/100\ {\text{K}}\right)\left(r/1{\text{ au}}\right)^{3}}{\left(M_{*}/M_{\odot }\right)\left({\bar {m}}/2{\text{ amu}}\right)}}}\ {\text{ au}}} with M ⊙ {\displaystyle M_{\odot }}

1704-480: Is the increase in altitude for which the atmospheric pressure decreases by a factor of e . The scale height remains constant for a particular temperature. It can be calculated by H = k B T m g {\displaystyle H={\frac {k_{\text{B}}T}{mg}}} or equivalently H = R T M g {\displaystyle H={\frac {RT}{Mg}}} where: The pressure (force per unit area) at

1775-536: The International Astronomical Union : the 15.6-kilometre-diameter (9.7 mi) Karzok crater and the 10.4-kilometre-diameter (6.5 mi) Pangboche crater . They are two of several suspected source areas for shergottites , the most abundant class of Martian meteorites . As a shield volcano , Olympus Mons resembles the shape of the large volcanoes making up the Hawaiian Islands . The edifice

1846-578: The Mars Express orbiter in 2004 indicate that lava flows on the northwestern flank of Olympus Mons range in age from 115 million years old (Mya) to only 2 Mya. These ages are very recent in geological terms, suggesting that the mountain may still be volcanically active, though in a very quiescent and episodic fashion. The caldera complex at the peak of the volcano is made of at least six overlapping calderas and caldera segments (pictured). Calderas are formed by roof collapse following depletion and withdrawal of

1917-514: The Noachian (4000 million years ago) was 500 times higher than today. Planetary scientists still debate whether these high rates represent the tail end of planetary accretion or a late cataclysmic pulse that followed a more quiescent period of impact activity. Nevertheless, at the beginning of the Hesperian, the impact rate had probably declined to about 80 times greater than present rates, and by

1988-661: The cut-off density ρ cut {\displaystyle \rho _{\text{cut}}} has the form ρ c u t ( r ) = ( μ 0 σ D r ) 2 ( B z 2 μ 0 ) ( Ω ∗ Ω K − 1 ) 2 {\displaystyle \rho _{\rm {cut}}(r)=(\mu _{0}\sigma _{D}r)^{2}\left({\frac {B_{z}^{2}}{\mu _{0}}}\right)\left({\frac {\Omega _{*}}{\Omega _{K}}}-1\right)^{2}} where These formulae give

2059-727: The ideal gas law and the hydrostatic equilibrium equation, gives: d ρ d z ≈ − G M ∗ m ¯ ρ z k T r 3 {\displaystyle {\frac {d\rho }{dz}}\approx -{\frac {GM_{*}{\bar {m}}\rho z}{kTr^{3}}}} which has the solution ρ = ρ 0 exp ⁡ ( − ( z h D ) 2 ) {\displaystyle \rho =\rho _{0}\exp \left(-\left({\frac {z}{h_{D}}}\right)^{2}\right)} where ρ 0 {\displaystyle \rho _{0}}

2130-545: The lunar maria . These "ridged plains" are interpreted to be basaltic lava flows ( flood basalts ) that erupted from fissures. The number-density of large impact craters is moderate, with about 125–200 craters greater than 5 km in diameter per million km . Hesperian-aged ridged plains cover roughly 30% of the Martian surface; they are most prominent in Hesperia Planum, Syrtis Major Planum , Lunae Planum, Malea Planum, and

2201-474: The solar mass , au {\displaystyle {\text{au}}} the astronomical unit and amu {\displaystyle {\text{amu}}} the atomic mass unit . As an illustrative approximation, if we ignore the radial variation in the temperature, T {\displaystyle T} , we see that h D ∝ r 3 / 2 {\displaystyle h_{D}\propto r^{3/2}} and that

Olympus Mons - Misplaced Pages Continue

2272-404: The 19th century. The astronomer Patrick Moore pointed out that Schiaparelli (1835–1910) "had found that his Nodus Gordis and Olympic Snow [Nix Olympica] were almost the only features to be seen" during dust storms, and "guessed correctly that they must be high". The Mariner 9 spacecraft arrived in orbit around Mars in 1971 during a global dust-storm. The first objects to become visible as

2343-539: The Hesperian, Mars changed from the wetter and perhaps warmer world of the Noachian to the dry, cold, and dusty planet seen today. The absolute age of the Hesperian Period is uncertain. The beginning of the period followed the end of the Late Heavy Bombardment and probably corresponds to the start of the lunar Late Imbrian period, around 3700 million years ago ( Mya ). The end of the Hesperian Period

2414-400: The Martian geologic record. As originally conceived, the Hesperian System referred to the oldest surfaces on Mars that postdate the end of heavy bombardment . The Hesperian was thus a time period of rapidly declining impact cratering rates. However, the timing and rate of the decline are uncertain. The lunar cratering record suggests that the rate of impacts in the inner Solar System during

2485-563: The Pre-Noachian, Noachian , Hesperian, and Amazonian. Geologic units lying below (older than) the Noachian are informally designated Pre-Noachian. The geologic time ( geochronologic ) equivalent of the Hesperian System is the Hesperian Period. Rock or surface units of the Hesperian System were formed or deposited during the Hesperian Period. System and period are not interchangeable terms in formal stratigraphic nomenclature, although they are frequently confused in popular literature. A system

2556-469: The Syria-Solis-Sinai Plana in southern Tharsis . Martian time periods are based on geologic mapping of surface units from spacecraft images . A surface unit is a terrain with a distinct texture, color, albedo , spectral property, or set of landforms that distinguish it from other surface units and is large enough to be shown on a map. Mappers use a stratigraphic approach pioneered in

2627-452: The Tharsis rise, which presented a higher-friction zone at the volcano's base. Friction was higher in that direction because the sediments were thinner and probably consisted of coarser grained material resistant to sliding. The competent and rugged basement rocks of Tharsis acted as an additional source of friction. This inhibition of southeasterly basal spreading in Olympus Mons could account for

2698-459: The atmospheric pressure at the summit of Mount Everest is 32,000 pascals, or about 32% of Earth's sea level pressure. Even so, high-altitude orographic clouds frequently drift over the Olympus Mons summit, and airborne Martian dust is still present. Although the average Martian surface atmospheric pressure is less than one percent of Earth's, the much lower gravity of Mars increases the atmosphere's scale height ; in other words, Mars's atmosphere

2769-412: The base of Olympus Mons and is thought to be due to the volcano's immense weight pressing down on the Martian crust. The depth of this depression is greater on the northwest side of the mountain than on the southeast side. Olympus Mons is partially surrounded by a region of distinctive grooved or corrugated terrain known as the Olympus Mons aureole. The aureole consists of several large lobes. Northwest of

2840-478: The beginning of the Late Hesperian the atmosphere had probably thinned to its present density. As the planet cooled, groundwater stored in the upper crust (mega regolith ) began to freeze, forming a thick cryosphere overlying a deeper zone of liquid water. Subsequent volcanic or tectonic activity occasionally fractured the cryosphere, releasing enormous quantities of deep groundwater to the surface and carving huge outflow channels . Much of this water flowed into

2911-456: The crust of Mars remains fixed over a stationary hotspot , and a volcano can continue to discharge lava until it reaches an enormous height. Being a shield volcano, Olympus Mons has a very gently sloping profile. The average slope on the volcano's flanks is only 5%. Slopes are steepest near the middle part of the flanks and grow shallower toward the base, giving the flanks a concave upward profile. Its flanks are shallower and extend farther from

Olympus Mons - Misplaced Pages Continue

2982-406: The detachment zones can produce giant landslides and normal faults on the volcano's flanks, leading to the formation of a basal escarpment. Further from the volcano, these detachment zones can express themselves as a succession of overlapping, gravity driven thrust faults. This mechanism has long been cited as an explanation of the Olympus Mons aureole deposits (discussed below). Olympus Mons lies at

3053-415: The disk increases in altitude as one moves radially away from the central object. Due to the assumption that the gas temperature in the disk, T , is independent of z , h D {\displaystyle h_{D}} is sometimes known as the isothermal disk scale height. A magnetic field in a thin gas disk around a central object can change the scale height of the disk. For example, if

3124-409: The dust began to settle, the tops of the Tharsis volcanoes, demonstrated that the altitude of these features greatly exceeded that of any mountain found on Earth, as astronomers expected. Observations of the planet from Mariner 9 confirmed that Nix Olympica was a volcano. Ultimately, astronomers adopted the name Olympus Mons for the albedo feature known as Nix Olympica. Olympus Mons is located between

3195-479: The early 1960s for photogeologic studies of the Moon . Although based on surface characteristics, a surface unit is not the surface itself or group of landforms . It is an inferred geologic unit (e.g., formation ) representing a sheetlike, wedgelike, or tabular body of rock that underlies the surface. A surface unit may be a crater ejecta deposit, lava flow, or any surface that can be represented in three dimensions as

3266-691: The edge of the Tharsis bulge, an ancient vast volcanic plateau likely formed by the end of the Noachian Period . During the Hesperian , when Olympus Mons began to form, the volcano was located on a shallow slope that descended from the high in Tharsis into the northern lowland basins. Over time, these basins received large volumes of sediment eroded from Tharsis and the southern highlands. The sediments likely contained abundant Noachian-aged phyllosilicates (clays) formed during an early period on Mars when surface water

3337-438: The end of the Hesperian, some 700 million years later, the rate began to resemble that seen today. Scale height In atmospheric , earth , and planetary sciences, a scale height , usually denoted by the capital letter H , is a distance ( vertical or radial ) over which a physical quantity decreases by a factor of e (the base of natural logarithms , approximately 2.718). For planetary atmospheres, scale height

3408-582: The equation for H given above to give: d P P = − d z H {\displaystyle {\frac {dP}{P}}=-{\frac {dz}{H}}} which will not change unless the temperature does. Integrating the above and assuming P 0 is the pressure at height z = 0 (pressure at sea level ) the pressure at height z can be written as: P = P 0 exp ⁡ ( − z H ) {\displaystyle P=P_{0}\exp \left(-{\frac {z}{H}}\right)} This translates as

3479-562: The following scale heights for representative air temperatures. These figures should be compared with the temperature and density of Earth's atmosphere plotted at NRLMSISE-00 , which shows the air density dropping from 1200 g/m at sea level to 0.125 g/m at 70 km, a factor of 9600, indicating an average scale height of 70 / ln(9600) = 7.64 km, consistent with the indicated average air temperature over that range of close to 260 K. Note: Approximate atmospheric scale heights for selected Solar System bodies: For

3550-516: The hydrostatic equilibrium equation is d P d z ≈ − G M ∗ ρ z r 3 {\displaystyle {\frac {dP}{dz}}\approx -{\frac {GM_{*}\rho z}{r^{3}}}} To determine the gas pressure, one can use the ideal gas law : P = ρ k B T m ¯ {\displaystyle P={\frac {\rho k_{\text{B}}T}{\bar {m}}}} with: Using

3621-448: The inflation of each chamber and uplift of parts of the volcano summit. Olympus Mons is structurally and topographically asymmetrical. The longer, more shallow northwestern flank displays extensional features, such as large slumps and normal faults . In contrast, the volcano's steeper southeastern side has features indicating compression, including step-like terraces in the volcano's mid-flank region (interpreted as thrust faults ) and

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3692-472: The large shield volcanoes on Mars, including Olympus Mons , had begun to form. Volcanic outgassing released large amounts of sulfur dioxide (SO 2 ) and hydrogen sulfide (H 2 S) into the atmosphere, causing a transition in the style of weathering from dominantly phyllosilicate ( clay ) to sulfate mineralogy . Liquid water became more localized in extent and turned more acidic as it interacted with SO 2 and H 2 S to form sulfuric acid . By

3763-421: The low gradients on the surface of the planet. Olympus Mons is the result of many thousands of highly fluid, basaltic lava flows that poured from volcanic vents over a long period of time (the Hawaiian Islands exemplify similar shield volcanoes on a smaller scale – see Mauna Kea ). Like the basalt volcanoes on Earth, Martian basaltic volcanoes are capable of erupting enormous quantities of ash . Due to

3834-499: The maximum height, H B {\displaystyle H_{B}} , of the magnetized disk as H B = h D ln ⁡ ( 1 + ρ 0 / ρ c u t ) , {\displaystyle H_{B}=h_{D}{\sqrt {\ln \left(1+\rho _{0}/\rho _{\rm {cut}}\right)}},} while the e-folding magnetic scale height, h B {\displaystyle h_{B}} ,

3905-628: The northern hemisphere where it probably pooled to form large transient lakes or an ice covered ocean. The Hesperian System and Period is named after Hesperia Planum , a moderately cratered highland region northeast of the Hellas basin. The type area of the Hesperian System is in the Mare Tyrrhenum quadrangle (MC-22) around 20°S 245°W  /  20°S 245°W  / -20; -245 . The region consists of rolling, wind-streaked plains with abundant wrinkle ridges resembling those on

3976-480: The northwestern edge of the Tharsis region and the eastern edge of Amazonis Planitia . It stands about 1,200 km (750 mi) from the other three large Martian shield volcanoes, collectively called the Tharsis Montes ( Arsia Mons , Pavonis Mons , and Ascraeus Mons ). The Tharsis Montes are slightly smaller than Olympus Mons. A wide, annular depression or moat about 2 km (1.2 mi) deep surrounds

4047-535: The ocean floor). The total elevation change from the plains of Amazonis Planitia , over 1,000 km (620 mi) to the northwest, to the summit approaches 26 km (16 mi). The summit of the mountain has six nested calderas (collapsed craters) forming an irregular depression 60 km (37 mi) × 80 km (50 mi) across and up to 3.2 km (2.0 mi) deep. The volcano's outer edge consists of an escarpment , or cliff, up to 8 km (5.0 mi) tall (although obscured by lava flows in places),

4118-527: The planet where surface units indicate a distinctive geological episode, recognizable in time by cratering age and stratigraphic position. For example, Hesperia Planum is the referent location for the Lower Hesperian Series. The corresponding geologic time (geochronological) units of the two Hesperian series are the Early Hesperian and Late Hesperian Epochs . An epoch is a subdivision of a period;

4189-510: The pressure decreasing exponentially with height. In Earth's atmosphere , the pressure at sea level P 0 averages about 1.01 × 10  Pa , the mean molecular mass of dry air is 28.964  Da and hence m = 28.964 Da × 1.660 × 10  kg/Da = 4.808 × 10  kg . As a function of temperature, the scale height of Earth's atmosphere is therefore H / T = k / mg = 1.381 × 10  J⋅K / ( 4.808 × 10  kg × 9.81 m⋅s ) = 29.28 m/K . This yields

4260-418: The reduced gravity of Mars compared to Earth, there are lesser buoyant forces on the magma rising out of the crust. In addition, the magma chambers are thought to be much larger and deeper than the ones found on Earth. The flanks of Olympus Mons are made up of innumerable lava flows and channels. Many of the flows have levees along their margins (pictured). The cooler, outer margins of the flow solidify, leaving

4331-422: The ridged plains overlie early to mid Noachian aged cratered plateau materials (pictured left). The Hesperian's upper boundary is more complex and has been redefined several times based on increasingly detailed geologic mapping. Currently, the stratigraphic boundary of the Hesperian with the younger Amazonian System is defined as the base of the Vastitas Borealis Formation (pictured right). The Vastitas Borealis

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4402-512: The structural and topographic asymmetry of the mountain. Numerical models of particle dynamics involving lateral differences in friction along the base of Olympus Mons have been shown to reproduce the volcano's present shape and asymmetry fairly well. It has been speculated that the detachment along the weak layers was aided by the presence of high-pressure water in the sediment pore spaces, which would have interesting astrobiological implications. If water-saturated zones still exist in sediments under

4473-410: The subsurface magma chamber after an eruption. Each caldera thus represents a separate pulse of volcanic activity on the mountain. The largest and oldest caldera segment appears to have formed as a single, large lava lake. Using geometric relationships of caldera dimensions from laboratory models, scientists have estimated that the magma chamber associated with the largest caldera on Olympus Mons lies at

4544-410: The summit in the northwestern direction than they do to the southeast. The volcano's shape and profile have been likened to a "circus tent" held up by a single pole that is shifted off center. Due to the size and shallow slopes of Olympus Mons, an observer standing on the Martian surface would be unable to view the entire profile of the volcano, even from a great distance. The curvature of the planet and

4615-530: The two terms are not synonymous in formal stratigraphy. The age of the Early Hepserian/Late Hesperian boundary is uncertain, ranging from 3600 to 3200 million years ago based on crater counts. The average of the range is shown in the timeline below. Stratigraphic terms are typically confusing to geologists and non-geologists alike. One way to sort through the difficulty is by the following example: One could easily go to Cincinnati, Ohio and visit

4686-449: The volcano itself would obscure such a synoptic view. Similarly, an observer near the summit would be unaware of standing on a very high mountain, as the slope of the volcano would extend far beyond the horizon, a mere 3 kilometers away. The typical atmospheric pressure at the top of Olympus Mons is 72 pascals , about 12% of the average Martian surface pressure of 600 pascals. Both are exceedingly low by terrestrial standards; by comparison,

4757-414: The volcano, the aureole extends a distance of up to 750 km (470 mi) and is known as Lycus Sulci ( 24°36′N 219°00′E  /  24.600°N 219.000°E  / 24.600; 219.000 ). East of Olympus Mons, the aureole is partially covered by lava flows, but where it is exposed it goes by different names ( Gigas Sulci , for example). The origin of the aureole remains debated, but it

4828-418: The volcano, they would likely have been kept warm by a high geothermal gradient and residual heat from the volcano's magma chamber. Potential springs or seeps around the volcano would offer many possibilities for detecting microbial life. Olympus Mons and a few other volcanoes in the Tharsis region stand high enough to reach above the frequent Martian dust-storms recorded by telescopic observers as early as

4899-451: The western hemisphere. The huge equatorial canyon system of Valles Marineris formed during the Hesperian as a result of these stresses. Sulfuric-acid weathering at the surface produced an abundance of sulfate minerals that precipitated in evaporitic environments , which became widespread as the planet grew increasingly arid. The Hesperian Period was also a time when the earliest evidence of glacial activity and ice-related processes appears in

4970-415: Was abundant, and were thickest in the northwest where basin depth was greatest. As the volcano grew through lateral spreading, low-friction detachment zones preferentially developed in the thicker sediment layers to the northwest, creating the basal escarpment and widespread lobes of aureole material ( Lycus Sulci ). Spreading also occurred to the southeast; however, it was more constrained in that direction by

5041-448: Was likely formed by huge landslides or gravity-driven thrust sheets that sloughed off the edges of the Olympus Mons shield. 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. During

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