Sunday, 19 April 2015

Methane storms as a possible cause of Titan’s equatorial dune fields.

Observations by the Cassini Space Probe have revealed vast dune fields, similar to those observed in the great sandy deserts of Earth, stretching around the equator of Saturn’s moon Titan. Surprisingly these appear to be formed by the actions of winds blowing west-to-east, while surface winds in the equatorial region of Titan, as on Earth, appear to blow overwhelmingly in an east-to-west direction.

In a paper published in the journal Nature Geoscience on 13 April 2015 and on the arXiv database at Cornell University Library on 14 April 2015, Benjamin Charnay of the Virtual Planetary Laboratory at the University of Washington and the Laboratoire de Météorologie Dynamique, Erika Barth and Scot Rafkin of the Southwest Research Institute, Clément Narteau of the Institut de Physique du Globe de Paris at the Université Paris-Diderot, Sébastien Lebonnois also of the the Laboratoire de Météorologie Dynamique, Sébastien Rodriguez of the Laboratoire Astrophysique, Instrumentation et Modélisation at the Université Paris-Diderot, Sylvain Courrech du Pont of the Laboratoire de Matière et Systèmes Complexes at the Université Paris-Diderot and Antoine Lucas also of the Laboratoire Astrophysique, Instrumentation et Modélisation at the Université Paris-Diderot describe a model of dune formation on Titan which invokes methane storms originating in the moon’s troposphere as a cause of dune formation.

Map of Titan’s dune orientation; radar-measured dune orientation vectors, showing the global eastward propagation and the divergence from the equator for latitudes higher than 10˚. Charnay et al. (2015).

Five kilometres above the surface of Titan, the winds of the moon’s troposphere flow in a constant west-to-east direction, making them an obvious candidate to explain any surface features flowing in a similar direction. However the troposphere of Titan is separated from the lower atmosphere by a boundary layer about 2 km above the moon’s surface, apparently preventing any direct influence on ground features by this layer.

Titan has a weather system driven by its methane cycle in much the same way that the Earth’s weather is driven by water. This results in frequent methane precipitation (rainfall) and even flowing rivers on the surface of the moon, the only place in the Solar System other than Earth where such activity has been discovered. However the equatorial region of Titan is apparently methane-arid, with few cloud systems observed and generally clear skies.

In September 2009 a massive storm with an upper atmospheric limit 10-30 km above the surface with a width of about 2000 km was observed to develop on Titan, coincident with the moon’s equinox. Climate simulations suggest that convergent atmospheric currents might cause similar storms to develop on the moon each equinox, i.e. twice a Titan year, which since a year on Titan is 29.5 Earth Years, would be every 14.75 of our years (14 years and 9 months). The storm travelled about 4000 km during the time it was observed; and a 2000 km storm travelling 4000 km could be expected to affect about 20% of Titan’s equatorial belt, suggesting that at least 40% of this belt could be influenced by such storms each year.

Charnay et al.’s model suggests that such storms could generate downdafts reaching down to the surface, possibly associated with precipitation. Downdrafts created by storms in the upper atmosphere will move in the direction of the layer that generates them regardless of prevailing conditions at the surface, generating winds known as gust fronts at their leading edges. The model suggests that this could lead to west-to-east winds with wind speeds of up to 10 meters per second maintained for up to nine hours. This is far in excess of normal east-to-west wind speeds at ground level in the equatorial region of Titan, thought to average around 0.5 meters per second and seldom to exceed one meter per second.

2D (altitude/longitude) simulation of the evolution of a storm under Titan’s conditions at equator during equinox. (a), (b), (c) and (d) are taken 1h, 1h40, 10h35 and 12h30 after the start of the simulation, respectively. The initial wind profile was derived from the Titan Institute Pierre Simon Laplace Global Climate Model. The initial methane humidity corresponds to a convective available potential energy of 500 J/kg. Colour bars indicate the mixing ratio of condensed methane in g/kg. The wind vectors are scaled to the axis. A reference vector of 10 m/s for zonal wind is shown. In (c) and (d), the vertical wind component is reduced by 80 % to better see the gust front. Charnay et al. (2015).

Since saltation, the movement of small particles at the surface by atmospheric currents, is driven by wind-speed (i.e. stronger winds can move more and bigger particles further), it is quite possible that infrequent strong winds can play a larger role in the formation of dunes (or other surface features) than weaker prevailing winds. The nature of the particles comprising the dunes in Titan’s equatorial region is unknown, but if a particle size of 300 μm (0.3 mm) is assumed then a windspeed of 0.9 meters per second would be needed to move particles by saltation, which the climate model used suggests may be exceeded by east-to-west winds for only 0.06% of the time, leading to a westward sand flux of 0.0015 square meters per year. Since the model includes sustained wind-speeds but not stronger gusts, Charnay et al. increased the wind-speed by 20% in their calculations, resulting in an annual westward sand transport of 0.018 square meters per year. This compares with a predicted eastward sand flux of 0.15 square meters per year, 2.7 times the larger figure derived for the westward flux, suggesting that episodic tropical storms could dominate sand transport and dune formation in this region. Were the particles to be larger than 300 μm (which does not seem unlikely) then there would be a much higher impact on the amount of sand moved by general circulation than by storm events (i.e. the larger the grain size the more the transportation of particles would be dominated by storm events).

See also…

NASA scientists have released an image of a 400 km long river on Saturn's moon Titan, imaged by the Cassini Space Probe during a flyby on 26 September 2012. The river meanders for some...

New Cassini Images of Titan, Tethys and Methone.

The Cassini Space Probe was launched on 15 October 1997 from Cape Canaveral Air Force Station and entered orbit around Saturn on 30 June 2004. It...

Dione is was discovered in 1684 by the Genovan (coming from the Republic of Genova, part of modern Italy) astronomer Giovanni Domenico Cassini, the forth moon of Saturn to be discovered.

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Saturday, 18 April 2015

Magnitude 5.2 Earthquake off the Paria Peninsula, Venezuela.

The United States Geological Survey recorded a Magnitude 5.2 Earthquake at a depth of 76.0 km roughly 15 km north of the the Paria Peninsula on the north coast of Venezuala, slightly before 9.55 pm local time on Wednesday 15 April 2015 (slightly before 2.55 am on Thursday 16 April, GMT). This was a large quake, but at some depth as well as some way offshore, and there are no reports of any casualties or damage, though the quake was felt over a large area, with people reporting feeling it across much of northeast Venezuela, as well as in Trinidad and Tobago, Grenada and St Lucya.

The approximate location of the 15 April 2015 Paria Peninsula Earthquake. Google Maps.

The Paria Peninsula forms part of the southern margin of the Caribbean Plate, which is moving eastward compared to the South American Plate, upon which the rest of Venezuela sits. This is not a smooth process, the two plates constantly stick together, then break apart as the pressure builds up, causing Earthquakes in the process. 

See also...

The United States Geological Survey recorded a Magnitude 6.1 Earthquake at a depth of 79.4 km roughly 20 km north of the the Paria Peninsula on the north...

Soufrière Hills is an active stratovolcano (singular, 'Hills' is part of the name; a single cone-shaped volcano with several summits) in the south of the island of Montserrat, in the Leeward Islands. The summit of the volcano rises 915 m above sea-level, and it has a...

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Friday, 17 April 2015

Macaca leucogenys, a new species of Macaque from Modog County in southeastern Tibet.

For a long time it was considered that there were two species of Macaques present in the forests of southeastern Tibet, Macaca assamensis assamensis (the Assam Macaque and Macaca mulatta (the Rhesus Macaque). However in recent years work by Indian researchers in Arunachal State (referred to in China as ‘Indian-controlled Tibet'), which shares continuous forests with southeastern Tibet, has led to the description a new species, Macaca munzala (the Arunchal Macaque) and the detection of a fourth species Macaca thibetana (the Tibetan Macaque), previously thought not to be present in the region. However not all primatologists in India have accepted these results, suggesting that instead the known species may be more variable than previously thought. In response to this, scientists on the Chinese side of the border began a series of observations of Macaques present there in 2013 and 2014, and set camera traps in the forests Modog County in southeastern Tibet. To their surprise this resulted in the discovery of what appears to be another species of Macaque in the region, distinguishable by its coat and genital anatomy.

In a paper published in the American Journal of Primatology on 25 March 2015, Cheng Li of the Imaging Biodiversity Expedition, Chao Zhao of the Institute of Eastern-Himalaya Biodiversity Research at Dali University and Peng-Fei Fan of the Faculty of Forestry at Southwest Forestry University formerly describe this new species as Macaca leucogenys, the White-cheeked Macaque.

Traditionally new species have been described by the assignation of type specimens in museums, against which other specimens can be compared to establish whether or not they belong to the same species. However the International Code of Zoological Nomenclature allows for the designation of photographs as types in the case of Primates, due to ethical concerns about killing wild specimens, and Li et al. take advantage of this provision to describe the new species from photographic data only, with the intention of obtaining museum specimens in the future.

Photo showing robust White-cheeked Macaque with brown to dark brown dorsal pelage and relative short tail. The end of the tail bends towards the ground in some individuals. White hair on cheeks and ears are visible. Li et al. (2015).

The White-cheeked Macaque has a relatively uniform brown colouration on its body, though the belly is lighter than the back. The hair on the muzzle is the same colour as the body, but the cheeks and ears are white. In older individuals these white hairs grow longer, and white hairs also appear on the snout. Juveniles lack white cheeks. The tail is hairless and tapering, being distinctly thicker at the base then the tip; in many individuals it has a distinct downwards kink close to it’s tip.

Family group of White-cheeked Macaques. Adult male in the right, adult female in the left and two small juveniles. Li et al. (2015).

White-cheeked Macaques were found in the forests of Madog County at altitudes of between 1395 m and 2700 m, an environment that ranges from tropical forests, through evergreen broadleaf forest and into mixed broadleaf-conifer forest, suggesting a degree of environmental flexibility. It may also be present in neighbouring counties of China or other Himalayan nations.

Map showing the rough distribution range of each species or subspecies of Macaca in southeast Tibet. Li et al. (2015).

At the moment all the forests of Modog County are protected by the Yarlung Zangbo Grand Canyon Nature Reserve, which prohibits destructive practices such as slash and burn agriculture. However local people in the area are known to kill Primates caught raiding crops, and also to occasionally actively hunt Macaques. More seriously the Chinese government is currently planning a series of hydroelectric dams in Modog County, including one which would completely flood the area where the White-cheeked Macaque. This threatens to directly destroy a large area of environment inhabited by the White-cheeked Macaque and other rare Primates, and in addition will bring a large number of workers into the area, which will lead to additional environmental disruption, by the building of roads, houses and other facilities for workers, as well as being likely to fuel a rise in the bushmeat trade in the area. Li et al. therefore call for more work to study and protect this important environment to be carried out as a matter of some urgency.

See also… new species of Titi Monkey from the Amazon Rainforests of Brazil.                            Titi Monkeys, Callicebus spp., are a large group of New World Monkeys distributed throughout much of the Amazonian and Atlantic Rainforests of South America. Views on their taxonomy have varied considerably...
Saki Monkeys of the genus Pithecia are found throughout the tropical forests of South America. The taxonomy of the group is poorly understood, as species are often both variable and similar to other species...

Burmese Snub-nosed Monkey found in China.
The discovery of the Burmese Snub-nosed Monkey, Rhinopithecus strykeri, was announced in January 2011 in a paper in the American Journal of...
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Asteroid 2015 FL passes the Earth.

Asteroid 2015 FL passed by the Earth at a distance of 7 597 000 km (19.8 times the average distance between the Earth and the Moon, or 5.08 % of the average distance between the Earth and the Sun), at about 0.50 am GMT on Saturday 11 April 2015. There was no danger of the asteroid hitting us, though had it done so it would have presented a genuine threat. 2015 FL has an estimated equivalent diameter of 130-410 m (i.e. it is estimated that a spherical object with the same volume would be 130-410 m in diameter), and an object of this size would pass through the atmosphere and directly impact the ground with a force of about 65-3000 megatons (roughly 3800-175 000 times the explosive energy of the Hiroshima bomb), causing devastation over a wide area and creating a crater 2-6 kilometers across, and resulting in global climatic problems that could last for years or possibly decades.
 The calculated orbit of 2015 FL. JPL Small Body Database.
2015 FL was discovered on 16 March 2015 (31 days before its closest approach to the Earth) by the University of Hawaii's PANSTARRS telescope on Mount Haleakala on Maui. The designation 2015 FL implies that it was the eleventh asteroid (asteroid L) discovered in the second half of March 2015 (period 2015 F).
2015 FL has an 1606 day orbital period and an eccentric orbit tilted at an angle of 15.7° to the plane of the Solar System, which takes it from 0.94 AU from the Sun (i.e. 94% of the average distance at which the Earth orbits the Sun) to 4.43 AU from the Sun (i.e. 443% of the average distance at which the Earth orbits the Sun, nearly three times the distance at which the planet Mars orbits the Sun). It is therefore classed as an Apollo Group Asteroid (an asteroid that is on average further from the Sun than the Earth, but which does get closer). This means that while close encounters between 2015 FL and the Earth are rare, it does have fairly frequent close encounters with Jupiter, with the last having occured in April 2012 and the next predicted for September 2047.

See also... 2015 FS33 passes the Earth.     Asteroid 2015 FS33 passed by the Earth at a distance of 9 377 000 km (24.4 times the average distance between the Earth and the Moon, or 6.27 % of the average distance between the Earth and the Sun), slightly before 8.00 pm GMT on Wednesday 8 April 2015. There was no danger of... 2015 FX284 passes the Earth.   Asteroid 2015 FX284 passed by the Earth at a distance of 18 250 000 km (47.5 times the average distance between the Earth and the Moon, or 12.2% of the average distance between the Earth and the Sun), slightly after 10.40 pm GMT on Tuesday 7 April... C/2012 F3 (PANSTARRS) reaches its perihelion.                                                                       Comet C/2012 F3 (PANSTARRS) reached its perihelion (the closest point on its orbit to the Sun) on Tuesday 7 March 2015, when it was 3.46 AU from the Sun (i.e. 3.46 times the average distance at which the Earth orbits the Sun). The comet is visible only with a...
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Thursday, 16 April 2015

Azhdarchid Pterosaur cervical vertebra from the Late Cretaceous of the Haţeg Basin in Transylvania.

Azhdarchids were long-necked, toothless Pterosaurs, which came to dominate Pterosaur assemblages in the Late Creataceous. They were large animals, often with wingspans in excess of 10 m, and appear to have favoured fully terrestrial environments (unlike many earlier Pterosaurs which lived in coastal environments).

In a paper published in the American Museum Novitates on 17 March 2015, Mátyás Vremir of the Department of Natural Sciences of the Transylvanian Museum Society, Mark Witton of the School of Earth and Environmental Sciences at the University of Portsmouth, Darren Naish of the National Oceanography Centre at the University of Southampton, Gareth Dyke, also of the National Oceanography Centre at the University of Southampton, and of the Lendület Behavioural Ecology Research Group at the University of Debrecen, Stephern Brusatte of the School of Geosciences at the University of Edinburgh, Mark Norrel of the Division of Paleontology at the American Museum of Natural History and Radu Totoianu of the Ioan Raica Municipal Museum, describe a mid-neck cervical vertebra from an unknown Azhdarchid Pterosaur from Bărbat Formation at Pui in Transylvania, part of the distinctive End-Cretaceous fauna of the Haţeg Basin.

The specimen is an almost complete cervical vertebra, slightly crushes at its posterior end and lacking a condyle. It is 89 mm in length, but was probably about 97-100 mm long when complete.

(Left) Photographs of LPV (FGGUB) R.2395, an almost complete cervical four from Pui, Haţeg basin, in anterior (A), dorsal (B), posterior (C), lateral (D), left lateral, inverted, (E) and right lateral (F) views. (Right) Interpretative drawing in anterior (A), ventral (B), dorsal (C), and right (D) and left lateral (E) views. Abbreviations: Cot, cotyla; DPrezygT, dorsal prezygapophyseal tubercle; Hyp, hypapophysis; Intzyg, interzygapophyseal area/space; NS, neural spine; Prezyg, prezygapophysis; Trab, trabecula; VPrezygT, ventral prezygapophyseal tubercle. Vremir et al. (2015).

The cervical vertebrae of Azhdarchid Pterosaurs are morphologically distinct; it is possible to identify the position of a vertebra from the neck of one of these animals by its shape. The specimen does not appear to have come from any previously described species, but by comparison to other members of the group feel that it is most likely to be the fourth vertebra (counting backwards from the skull).

While Vremir et al. believe the specimen to come from a previously described species of Pterosaur, they refrain from describing it as a new species due to the fragmentary nature of the material. It appears to have belonged to an individual smaller than any previously described species from the Haţeg Basin, with a shorter and stouter neck (which would have enabled it to take different prey). However it is also apparently from a young animal, and young Azhdarchid Pterosaurs are known to have had shorter necks than mature adults (unlike Birds, Pterosaurs took several years to reach maturity, and were capable of flying long before they reached their full size), and the fourth vertebra is not known in many Azhdarchid species, making direct comparison to other specimens difficult.

See also…

The Loma del Pterodaustro lake deposits of Central Argentina have produced large numbers of the Pterosaur Pterodaustro guinazui...

The Pterosaur Zhenyuanopterus longirostris was described from a single specimen from the Early Cretaceous Yixian Formation (part of the Jehol....

Among the many remarkable fossils of the Jehol Biota Lagerstätte of northeast China a number of well preserved Pterosaurs have been discovered. One of these, Feolongus youngi, from the Yixian Formation of western Liaoning Province, is thought to have been...

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Thousands left without water after Mexico oil spill.

As many as 200 000 people have been left without water supplies after a spill from an oil pipeline servicing the Agave 32 Petrochemical Complex in Tabasco State in southern Mexico. The spill was detected on Monday 13 April 2015, when drivers on the Villahermosa–Jalapa Highway reported a strong petrol-like smell, and was found to have contaminated around 60 km² of pastures and farmland, and to have reached the Teapa River, which flows through the communities of Puyacatengo Norte, Emiliano Zapata, and Huasteca. Storage plants at a local water-treatment plant were also found to be contaminated with oil, leading to supplies to domestic customers being cut; residents of the affected areas are currently being supplied by water from trucks provided by the state government.

Workers from Petróleos Mexicanos inspecting the damaged pipeline which produced the leak. The News: Mexico.

Investigators from Petróleos Mexicanos (Pemex), who operate the pipeline, have attributed the leak to the activities of oil thieves, who drill into pipelines in order to steal oil, but seldom have the ability or inclination to seal pipelines when they have finished. Oil theft is a rising problem in Mexico, as in many other countries, as high oil prices and a large section of the population surviving on very low incomes makes the pipelines an increasingly tempting target. The problem has become so severe that Pemex no longer transports finished fuel oils through such pipelines, though it still uses them for untreated crud, which is less easy to use.

The approximate location of the Agave 32 Petrochemical Complex. Google Maps.

See also...

Four people are confirmed to have died following a fire on the Abkatun Permanente Oil Platform in the Gulf of Mexico on Wednesday 1 April 2015. Between 16 and 45 further people are reported to have sustained injuries (accounts from different sources vary), with two...

Three workers have died following an explosion at an oil rig near Rankin in Upton County, Texas, on Tuesday 10 March 2015. The men have been named as Rojelio Salgado and Arturo...

Four people were taken to hospital with minor injuries and four more were subjected to contamination procedures following an explosion at a gasoline...

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Wednesday, 15 April 2015

(Relatively) recent volcanic activity in the Southern Highlands of Mars.

The planet Mars formed about 4.5 billion years ago, and is thought to have been highly volcanically active in its early history. However due to its smaller size it is thought to have cooled much more rapidly than the Earth, with volcanism ceasing in most areas by the end of the Noarchian Epoch (about 3.7 billion years ago), with activity persisting in areas such as the Hesperian ridged plains and Tyrrhenus and Hadriacus Montes till about 3.5 billion years ago. The youngest lavas in the two main Martian volcanic provinces, Tharsis and Elysium are thought to be low-viscosity basaltic lavas, i.e. lavas that reached the surface in a hot, runny state then cooled rapidly on exposure to the atmosphere. More viscous, evolved lavas (lavas that have risen to the surface slowly, cooling and losing minerals which crystalize at high temperatures) are thought to be rare on Mars.

In a paper published in the journal Earth and Planetary ScienceLetters on 1 April 2015, Petr Brož of the Institute of Geophysics of the Academy of Sciences of the Czech Republic and the Institute of Petrology and StructuralGeology at Charles University in Prague, Ernst Hauber of the Institute of Planetary Research, Thomas Platz of the Institute of Geological Sciences at the Freie Universität Berlin and the Planetary Science Institute and Matt Balme also of the Planetary Science Institute, and of the Open University, describe a series of small-scale volcanic edifices in the Terra Sirenum region of the Martian Southern Highlands, which appear to have been formed by the action of viscous, highly evolved lavas during the mid-Amazonian Epoch, i.e. less than a billion years ago.

The Terra Sirenum is a highland region within the proposed former Eridania paleolake, crossed by east-west trending radial graben-systems (longitudinal depressions caused by stretching and thinning of the Martian crust) which may be associated with unexposed volcanic dykes (intrusive volcanic lavas running forming horizontal channels), derived from Arsia Mons 3700 km away, as well a series of wrinkle-ridges interpreted as fault-propagation folds associated with deformation caused by contraction of the crust.

Regional map of part of the southern hemisphere on Mars. The cyan colordelineates the extent of the proposed Eridania Lake based on the 1100m contour. Position of investigated area is marked by dashed box and clearly the area lies inside the proposed borders of the former lake. Brož et al. (2015).

The putative volcanic structures lie within an unnamed depression measuring approximately 150 km by 30 km, with all bar one of these within a further depression located inside this. The volcanic structures comprise three volcanic domes (A, B & C), all located within the inner depression, with A and B located on different sinuous wrinkle-ridges, which rise tens of meters above the surrounding plains, and two volcanic cones (T1 &T2), with Cone T1 sitting outside the inner depression on the rim of an ancient, highly eroded impact crater, which is roughly 110 km in diameter, and Cone T2 within the inner depression. In addition there are four flows of apparent volcanic material associated with these structures (Flows 1-4). Flow 1 may originate from Cone T1, though this area is also intersected with other flows, thought to be related to a 6 km diameter impact crater rather than any volcanic structure, making its interpretation complex; Flow 2 is elongate and appears to originate from Dome A, Flow 3 is roughly circular and surrounds Dome B and Dome C, though its precise origin is unclear, and Flow 4 is again elongate and appears to originate from Cone T2.

THEMIS-IR daytime (a), nighttime (b) and interpretational map of the study area (c). The thermal contrast between the two upper images (a, b) suggests the presence of flow structures associated with cones and domes. Note the wrinkle ridges crossing the basin. The cross-section shows the stratigraphic relations of the investigated edifices with underlying units. Brož et al. (2015).

Cone T1 is about 3 km in diameter and about 230 m in height. It is breached to the south, giving rise to a flow apron 8.5 km wide and 100-130 m thick, which partially covers the lower flanks of the cone. Two small impact craters, 1.3 and 0.8 km in diameter, are located on this flow apron.

(a)    Cone T1 with associated flow apron. (c) Detail of Cone T1 central vent from flow aprons material erupted to the surface. Brož et al. (2015).

Cone T2 is about 3 km in diameter and 290 m in height, and breached to the east, giving rise to a flow apron measuring 12.5 km from north to south, with four distinct lobes. The margins of these lobes appear to overlap, suggesting that the apron was formed by multiple eruptive episodes. The source of Flow 4 lies beneath these aprons; Flow 4 appears to originate from Cone T2 and flows roughly 50 km to the southwest, measuring 1-8 km wide and 30-50 m thick; it appears to have originally flowed to the west then been deflected southward when it encountered a wrinkle-ridge.

(b) Cone T2 with associated flow apron. (d) Detail of Cone T1 central vent from flow aprons material erupted to the surface. (e) Edge of overlapping flow aprons. Brožet al. (2015).

Dome A is a 2.5 km diameter mound located on top of a wrinkle ridge. Flow 2, which is about 5 km long and about 300 m wide appears to originate from this dome and spread to the southeast.

 Image of Dome A with marked Mars Orbiter Laser Altimeter Precision Experiment Data Records (MOLA PEDRs) and associated topographic profiles. Part of the Dome A seems to collapse and propagate in eastern direction. Brož et al. (2015).

Dome B is approximately 5 km by 7 km and 390 m in height, being highest in the north. It is located on top of a wrinkle-ridge, and appears to extend some way to the south along the crest of this ridge. It is irregular in shape, with four deeply incised valleys dividing the dome into four portions. It is surrounded by flow features, some of which are shared with Dome C, superimposed upon surrounding terrain which appears to be a single ancient unit with a dense covering of impact craters. The western margin of the flow apron surrounding Dome B has a 3 km impact crater, largely infilled with debris; several smaller impact craters are also located on this apron, and on Dome B itself.

Image of Dome B with close up details. (a) Detail of Dome B and surrounding flow and marked position of HiRISE image ESP_033977_1385 with marked positions of MOLA PEDRs and associated topographic profiles. (b) Detail of HiRISE image showing the contact between the northwestern edge of the dome and the underlying unit. Large boulders forming the dome itself and aeolian deposits at the top of the dome together with modification by gully activities are clearly visible. (c) Detail of the bedrock on which Dome B is superposed as exposed by an 80mhigh scarp. Pristine fracture morphologies suggest ongoing scarp erosion. Note that the talus is mainly formed by fine-grained material and small amounts of boulders less than 6metres large (marked by gray arrows), larger blocks are missing. The tensile fractures parallel to the scarp in the capped unit (marked by white arrows) are similar to fractures associated with rotational block-fall landslides known from Earth. (d) Detail of HiRISE image showing another part of the scarp. Again, no large blocks of fallen rocks are visible and the talus is composed mainly of finer particles and smaller boulders (marked by gray arrows). Two white arrows indicate small grooves, which might have formed by ongoing aeolian erosion. These grooves show that the exposed material is susceptible to erosion. Brožet al. (2015).

Dome C is roughly 3.5 km by 6 km and 530 m in height, again being higher closer to its northern margin.

Image of Dome C and surrounding flow. (a) The dome edifice is clearly surrounded by a flow structure that has steep edges, as demonstrated by the shadows on the southern margin. White arrow marks scarp on the edge of Flow 3. Position of MOLA PEDRs marked by lines and HiRISE image ESP_026474_1385 marked by dashed rectangle. (b) Detail of HiRISE image covering part of dome flanks (left part of image b) and flow structure (right part). Note large boulders forming the dome itself and aeolian deposits forming Transverse Aeolian Ridges (marked by white arrow). (c) The edge of the flow structure on the border with surrounding older, flat layer. The margin of the internal flow is formed by large-scale boulders that are partly covered by aeolian material (marked by white arrow). The older unit contains small Transverse Aeolian Ridges. Brož et al. (2015).

The ages of deposits on other planets are usually worked out by measuring the density of impact craters on those deposits, since impacts are thought to have occurred at a steady rate for much of the history of the Solar System. However none of the volcanic deposits examined by Brož et al. were extensive enough to use of this method. Instead the ages of the deposits were worked out by their stratigraphic relationships with other deposits for which age estimates were available; this is possible because a rock formation must be younger than a bed lying beneath it and older than a bed laid down on top of it, enabling geologists to estimate the age of geological strata in the absence of direct data.

Using this method it was determined that the flow apron associated with Cone T1 is approximately 600-800 million years old, while Flow 1 (also associated with Cone T1) is approximately 560-760 million years old. The flow apron around Cone T2 is estimated to be 370-570 million years old, while Flow 4, which originates beneath this flow, is 420-520 million years old. It was not possible to obtain dates for the dome structure, but these are thought to share a common origin with the cone structures, are therefore thought to be of similar ages.

Absolute model ages of (a) the crater’s ejecta and Flow 1, and (b) Cone T2, and Flow 4. (a) The cumulative crater size-frequency curves indicate an absolute model age 660  ± 100 Ma for Flow 1 and 700  ± 100 Ma for the crater’s ejecta. (b) The cumulative crater size-frequency curves indicate an absolute model age of 470  ± 100 Ma for Cone T2 and 470  ± 50 Ma for Flow 4. Note that for Flow 4 a resurfacing correction was applied to exclude larger craters, which underlie, and therefore predate Flow 4. Note the panels above the cumulative crater size-frequency plots represent the randomness analyses. Brož et al. (2015).

A spectrographical analysis of the mineral composition of exposed boulders on Domes D and C and Flow 3 suggests that these have compositions with low olivine abundances and moderate levels of pyroxene. Such mineral compositions are typical for terrestrial lava domes, and are associated with mature lavas; lavas that have been cooling for some time close to the surface before being extruded and have a distinctive mineralogical composition because of this (on smaller, chillier Mars such cooling may have occurred deeper within the planet). This is quite different from previous small volcanic structures recorded on Mars, such as scoria cones and tuff rings, which on Earth are typically formed by the eruption of younger, less viscous lavas. The margins of the flows are also quite steep, in places up to 20°, which is also indicative of more viscous mature lavas, and quite different from previously observed basalt flows in the Tharsis or Elysium volcanic provinces, which show very gentle flank slopes.

See also…

Hydrated minerals (minerals containing water) are considered to be evidence of the former presence of liquid water on Mars. They have been observed at a...
Landslides on Mars typically have much greater runout distances than those on Earth, due to the planets lower gravity and thinner atmosphere. This can lead to areas of layered deposits from different landslides quite distant from the source, particularly within the larger canyons on Mars. Since it is possible to produce approximate ages for such deposits based upon the number of impact...
The surface of Mars has been observed continuously by the Mars Orbiter Camera from 1997 to 2006 and the Mars Reconnaissance Orbiter since 2006. During the time that these observations have been occurring around 200 new impact craters have been observed on the surface of the planet; most of them in dusty areas, where they are easily detected due to the dark blast patterns that surround fresh impacts in these...
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