28 results found
Ghail RC, Hall D, Mason PJ, et al., 2018, VenSAR on EnVision: Taking earth observation radar to Venus, International Journal of Applied Earth Observation and Geoinformation, Vol: 64, Pages: 365-376, ISSN: 0303-2434
Airey MW, Mather TA, Pyle DM, et al., 2017, The distribution of volcanism in the Beta-Atla-Themis region of Venus: its relationship to rifting and implications for global tectonic regimes, Journal of Geophysical Research: Planets, Vol: 122, Pages: 1626-1649, ISSN: 2169-9097
A new analysis of the spatial relationships between volcanic features and rifts on Venusprovides new constraints on models of planetary evolution. We developed a new database of volcanicfeatures for the Beta-Atla-Themis (BAT) region and used nearest neighbor measurements to determinerelationships between different types of volcanic features and the rifts. Nearest neighbor analysis shows thatall the dome-type and corona-type subpopulations tend to cluster. Rift associations were inferred from thedeviation of a feature’s population distribution (as a function of distance from rift) from that of a randompopulation. Dome-type features in general have no discernible relationship with rifts. Most corona-typefeatures have a strong association with rifts, with intermediate and large volcanoes also tending to occurclose to or on rifts. Shield fields, on the other hand, tend to occur away from rifts. Our new evidencesupports classifications of rifts on Venus into different types, possibly by age, with a shift from globallydispersed (more uniform) volcanism toward the more rift-focused distribution, which suggests a shiftin tectonic regime. Our observations are consistent with recent models proposing the evolution of Venusfrom a stagnant lid regime to a subcrustal spreading regime. We also present evidence for a failed rift onVenus and note that this process may be analogous, albeit on a larger scale, to a proposed model for theevolution of the East African rift system.
Toms E, Mason PJ, Ghail RC, 2016, Drift-filled hollows in Battersea: investigation of the structure and geology along the route of the Northern Line Extension, London, QUARTERLY JOURNAL OF ENGINEERING GEOLOGY AND HYDROGEOLOGY, Vol: 49, Pages: 147-153, ISSN: 1470-9236
Airey MW, Mather TA, Pyle DM, et al., 2015, Explosive volcanic activity on Venus: The roles of volatile contribution, degassing, and external environment, PLANETARY AND SPACE SCIENCE, Vol: 113, Pages: 33-48, ISSN: 0032-0633
Ghail R, 2015, Rheological and petrological implications for a stagnant lid regime on Venus, PLANETARY AND SPACE SCIENCE, Vol: 113, Pages: 2-9, ISSN: 0032-0633
Ghail RC, Jacqueline S, Mason PJ, 2015, Identification of Ground Engineering Hazards in London Through the Use of Predictive 4D Geomodelling Tools, 12th International IAEG Congress, Publisher: SPRINGER INT PUBLISHING AG, Pages: 907-911
Ghail RC, Mason PJ, Skipper JA, 2015, The geological context and evidence for incipient inversion of the London Basin, Pages: 3523-3528
© The authors and ICE Publishing: All rights reserved, 2015. A reappraisal of ground investigation data across London reveal that a range of unexpected ground conditions, encountered in engineering works since Victorian times, may result from the effects of ongoing inversion of the London Basin. Site investigation borehole data and the distribution of river terrace deposits of the Thames and its tributaries reveal a complex pattern of block movements, tilting and dextral transcurrent displacement. Significant displacements (∼10 m) observed in Thames terrace gravels in borehole TQ38SE1565 at the Lower Lea Crossing, showing that movement has occurred within the last ∼100 ka. Restraining bends on reactivated transcurrent faults may explain the occurrence of drift filled hollows, previously identified as fluvially scoured pingos, by faulting and upward migration of water on a flower structure under periglacial conditions. Mapping the location of these features constrains the location of active transcurrent faults and so helps predict the likelihood of encountering hazardous ground conditions during tunnelling and ground engineering.
Ghail RC, Wilson L, 2015, A pyroclastic flow deposit on Venus, Geological Society Special Publication, Vol: 401, Pages: 97-106, ISSN: 0305-8719
© The Geological Society of London 2015. Explosive volcanism on Venus is severely inhibited by its high atmospheric pressure and lack of water. This paper shows that a deposit located near 16°S, 145°E, here referred to as Scathach Fluctus, displays a number of morphological characteristics consistent with a pyroclastic flow deposit. These characteristics, particularly the lack of channelization and evidence for momentum- rather than cooling-limited flow length, contrast with fissure-fed lava flow deposits. The total erupted volume is estimated to have been between 225 and 875 km 3 but this may have been emplaced in more than one event. Interaction between Scathach Fluctus and a small volcanic cone constrains the flow velocity to 48 ms -1 , and plausible volatile concentrations to at least 1.8 wt% H 2 O, 4.3 wt% CO 2 or 6.1 wt% SO 2 , the latter two values implying that magma was sourced directly from the mantle. The deposit has radar characteristics, particularly an exponential backscatter function, that are similar to those of nearly half the planetary surface, implying that pyroclastic deposits may be much more common on Venus than has been recognized to date, and suggesting both a relatively volatile-rich mantle and a volcanic source for atmospheric SO 2 .
Mason PJ, Ghail RC, Bischoff C, et al., 2015, Detecting and monitoring small-scale discrete ground movements across London, using Persistent Scatterer InSAR (PSI), XVI ECSMGE, Publisher: ICE Publishing
The geology of London is surprisingly poorly understood and, until recently, has been accepted as that of an unfaulted subsidingintraplate basin. The detection of deformation in such quiescent intraplate regions is, however, rather difficult since the movementrates are at least an order of magnitude less than those at plate margins. Growing evidence from across the capital indicates that London'sground conditions are considerably more complex than expected and that faulting is almost always involved.PSInSAR is a developing technique widely used to detect and monitor ground subsidence, especially in urban settings, the movements ofwhich may be up to tens of millimetres. This work focuses on the detection of smaller scale ground movements (of a few millimetres),which we believe are caused by fault-controlled intraplate adjustments, using PSInSAR.The London PSInSAR dataset derives from an imaging SAR archive spanning 18 years (1992 - 2000 and 2001 to 2010). Our preliminaryfindings have revealed systematic patterns of both vertical and horizontal ground displacement. These displacements appear to be faultconstrained and fit the predicted framework of Caledonian, Variscan/Alpine structures known to exist across southern Britain. More detailedanalysis has revealed some surprising patterns, which hint at discrete movements rather than continuous 'creep' over the 18 year period;we believe these are driven by basement faults beneath an inverting London basin.
Ghail RC, 2014, Being a Chief Executive Officer, The UK Space Design Competition, Editors: Perry, Greenwood, Publisher: Penelope Corporation, ISBN: 0985538147
Newman TG, Ghail RC, Skipper JA, 2013, Deoxygenated gas occurrences in the Lambeth Group of central London, UK, QUARTERLY JOURNAL OF ENGINEERING GEOLOGY AND HYDROGEOLOGY, Vol: 46, Pages: 167-177, ISSN: 1470-9236
Standing J, Ghail R, Coyne D, 2013, Gas generation and accumulation by aquifer drawdown and recharge in the London Basin, QUARTERLY JOURNAL OF ENGINEERING GEOLOGY AND HYDROGEOLOGY, Vol: 46, Pages: 293-302, ISSN: 1470-9236
Ghail R, 2009, A practical method for balancing modal provision on congested urban corridors, Traffic Engineering and Control, Vol: 50, Pages: 409-412, ISSN: 0041-0683
Many urban corridors are confined by historical constraints that limit the space available for each mode, causing congestion and crowding. Planners and engineers have often sought to optimise the space available for general traffic and more recently buses because the modelling tools and data are readily available to quantify the improvements possible. The lack of these tools and data for pedestrians and cyclists has led to the historical shift of urban centres from pedestrian dominated to traffic dominated. This paper presents a fresh approach to the problem by assessing journey time delay on the basis of unit time rather than unit distance, which compensates for the disparity in average speed between modes. The principle uncertainties result from a lack of data on the speed of cyclists in different conditions, for which further study is recommended, and the incorporation of freight into the assessment. The method is intended for guidance and is not prescriptive; issues such as road safety, DDA compliance, streetscape, etc, must also be considered by the planner/engineer. However, a simple worked example of a hypothetical average London street illustrates the key benefit of this new method in providing guidance on achieving the best balance between general traffic and bus lanes, cycle paths and footways, based on the available corridor width and number of people moved by mode. Further application in the provision of crossings, street furniture, and cycle paths is discussed. This practical method is recommended for use by planners and engineers to provide useful guidance at an early stage in the design process.
Bray VJ, Bussey DBJ, Ghail RC, et al., 2007, Meander geometry of Venusian canali: Constraints on flow regime and formation time, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 112, ISSN: 0148-0227
Cochrane CG, Ghail RC, 2006, Topographic constraints on impact crater morphology on Venus from high-resolution stereo synthetic aperture radar digital elevation models, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 111, ISSN: 0148-0227
Preston LJ, Genge MJ, Ghail R, 2006, Microbial structures in hydrothermal deposits as biomarkers for Mars, 69th Annual Meeting of the Meteoritical Society, Publisher: METEORITICAL SOC, Pages: A143-A143, ISSN: 1086-9379
Tuckwell GW, Ghail RC, 2003, A 400-km-scale strike-slip zone near the boundary of Thetis Regio, Venus, EARTH AND PLANETARY SCIENCE LETTERS, Vol: 211, Pages: 45-55, ISSN: 0012-821X
Ghail RC, 2002, Structure and evolution of southeast Thetis Regio, JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS, Vol: 107, ISSN: 0148-0227
Ghail RC, 2002, Structure and evolution of southeast Thetis Regio, Journal of Geophysical Research E: Planets, Vol: 107, Pages: 4-1, ISSN: 0148-0227
The highland terrain in southeast Thetis Regio consists of a series of thrust faults and conjugate graben that would usually be classified as tesserae. Unusually, this small area of tesserae is younger than the adjacent plains, a conclusion strengthened by modification of Jumaisat crater, a parabolic dark-halo crater > 75 Myr old. Two structural belts are distinguished, the eastern ridged terrain and the central plateau, separated by conjugate graben. Unlike most terrestrial mountain belts, the thrusts in southeast Thetis are outward dipping, implying obduction of the eastern plains onto Thetis. This most likely results from the buoyancy of the Venusian lithosphere, which inhibits subduction. A simple two-stage orogenic model is inferred. Plains crust, driven by extension in Diana Chasma, initially overrides higher-standing tesserae crust in southeast Thetis. Through interaction with a plume, or perhaps through convective instability of the lower lithosphere, a plateau forms that resists further compression and that exhibits extensive volcanism. A new area of thrusting in the ridged terrain develops, while the plateau starts to collapse along graben, the larger of which are filled with lavas. The core of Thetis Regio appears to be surrounded by other tectonic units like southeast Thetis, indicating a piecemeal construction similar to terrestrial continents.
De Oliveira MRR, Gil PJS, Ghail RC, A novel orbiter mission concept for venus with the envision proposal, International Astronautical Congress, IAC, Publisher: Elseiver, ISSN: 0074-1795
In space exploration, planetary orbiter missions are essential to gain insight into planets as a whole,and to help uncover unanswered scientific questions. In particular, the planets closest to the Earthhave been a privileged target of the world’s leading space agencies. EnVision is a mission proposalwith the objective of studying Earth’s closest neighbor. Designed for Venus and competing for ESA’snext launch opportunity, the proposal already went through the selective technical review for the M4launch opportunity, and was submitted to the M5 call, incorporating feedback from ESA. The maingoal is to study geological and atmospheric processes, namely surface processes, interior dynamics andatmosphere, to determine the reasons behind Venus and Earth’s radically different evolution despite theplanets’ similarities. To achieve these goals, the operational orbit selection is a fundamental elementof the mission design process. The design of an orbit around Venus faces specific challenges, such asthe impossibility of choosing Sun-synchronous orbits. In this paper, an innovative genetic algorithmoptimization was applied to select the optimal orbit based on the parameters with more influence in themission planning, in particular the mission duration and the coverage of sites of interest on the Venusiansurface. After summarizing the EnVision proposal’s mission concept for Venus, the optimization andinnovation of the operational orbit design will be analyzed in terms of its benefits to the mission.
Ghail RC, Ice Crust Thickness and Internal Composition of Europa, 29th Lunar and Planetary Science Conference
The radius (1569 km), mass (4·868 x 1022 kg) and I/MR2 (0·264, E4; 0·347, E6), have been determined from data returned Galileo encounters, and provide useful constraints on bulk composition models of Europa. I present new physical and chemical models derived from known meteoritic compositions expected to be representative of Europa’s bulk composition. A core is differentiated, along with a mantle, crust and cryosphere. Using a modified CIPW norm method, the mineralogy of the crust and of the depleted and fertile mantle is derived, and hence the density of each layer is found. The thickness of the crust and cryosphere are adjusted to match the observed mass, radius and moment of inertia of Europa. Radiogenic and tidal energy production rates are calculated and used to define two possible thermal structures of the crust and mantle.
Ghail RC, The composition and internal structure of Europa, 28th Lunar and Planetary Science Conference
The bulk density of Europa, as derived from Voyager data, indicated a bulk composition similar to the Moon or Mars but with the addition of 5 to 10% water. The accepted view was that this water is distributed as a layer of ice ~150 km thick  at the surface. Debate has continued as to whether this layer is partly liquid. Ransford  was the first to suggest that this model may be too simplistic and proposed that there may also be a hydrated silicate layer. However, a full cosmochemical treatment of Europa (or any Galilean satellite) has not be conducted. This abstract presents the results of a simple model of Europa derived from the composition of a chondrite appropriate to its position in the proto-jovian nebula. This model assumes full differentiation into core, mantle, crust and cryosphere and that the internal temperature distribution is such that hydrated silicates are stable to their pressure limited phase boundary (at about 2 GPa). The model has been refined to fit the within the uncertainty limits of mass and radius but is not unique and other possible compositions have yet to be tested. The bulk composition used in the model is listed in Table 1 by weight percent and mole fraction.
Ghail RC, Hall D, VenSAR: A multi-functional S-band radar for the EnVision mission to Venus, 36th ESA Antenna Workshop
The EnVision science case requires an instrument capable of providing global stereo images at 10-50 m resolution, phase information from at least 20% of the surface for interferometry, as well as the ability to provide 1-10 m resolution images of specific targets in the C- to S-band range (X-band does not penetrate through the atmosphere to the surface of Venus). VenSAR is adapted from the individual phase centre design of NovaSAR-S, which offers much greater flexibility that can be optimised for Venus science. In addition, its S-band wavelength offers an acceptable compromise between InSAR resolution and atmospheric stability. The use of an 'off-the-shelf' system, adapted for use at Venus, saves cost and provides for directly comparable data from Venus and Earth at a resolution two orders of magnitude better than Magellan, for the first time allowing the direct measurement of rates of tectonic and volcanic processes on another planet.
Ghail RC, Hutchison JE, An Alluvial Fan at Apollinaris Patera, Mars, http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1775.pdf, 34th Lunar and Planetary Science Conference
Apollinaris Patera, Mars (7˚S,173˚E), is an intermediate sized volcano (~6 km high, 150 km diameter) with a large (200-km long) fan-like deposit on its southern flank. This fan is deeply incised and originates from a single breach in the rim of the summit caldera. New topographic and multispectral image data reveal that this fan is alluvial, implying a long-lived source of (volcaniclastic) sediment and water (probably from a caldera lake).
Ghail RC, Tuckwell GW, The Deformation of Eastern Ovda Regio – Collision and Complexity, Lunar and Planetary Science
Western Aphrodite Terra, Venus, consists of two highland tesserae (or crustal plateaux), Ovda and Thetis Regionnes, separated by lower-lying fractured plains. The origin of highland plateaux has been the subject of debate, principally between the downwelling model of , which proposes that they form above mantle downwellings that shorten and thicken the ductile lower crust, and the upwelling model of , which proposes that they are produced by mantle plumes that thicken the crust by flood volcanism. These models make opposite predictions about the relationship between extensional and compressional features. A particular prediction of  is that tensile fractures and graben (both collectively referred to as ribbons) are formed by doming of a thin brittle layer above a large mantle upwelling. Later collapse of this dome produces circumferential folds. Here we examine the regional structure of Eastern Ovda and attempt to produce a deformation model to fit the observations. Specifically, we consider the location and orientation of ribbon and fold structures, and the late-stage deformation recorded in the intra-tessera basins.
Linde-Arias E, Harris D, Ghail RC, Engineering Geology and Tunnelling in the Limmo Peninsula, East London, Quarterly Journal of Engineering Geology and Hydrogeology, ISSN: 1470-9236
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