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Laboratory experiments have been performed to demonstrate significant levels of oxygen depletion within samples of Upnor Formation of the Lambeth Group deposits. These have been used to explain the reasons for several incidences of confined space hypoxia during underground construction within the stratum beneath London. Further investigation, using a relatively small-scale field pump-out test, revealed the rapid effects of dewatering on the generation of hypoxic gas (within the ground) and that the amount of oxygen falls to fatal levels within a very short time after commencement of pumping. Monitoring of boreholes during ground investigation for the Thames Tideway Tunnel has indicated barometric control on the release of hypoxic gas from installations within granular deposits of the Lambeth Group, namely the Upnor Formation, as well as channel sand deposits within the Laminated Beds. In these, reduced levels of oxygen coincide with low and/or falling barometric pressure. Continuous 24-hour monitoring demonstrates that the reduction is almost instantaneous and has serious implications for the Health and Safety of underground construction personnel.

Structures in the basement beneath the London Basin affect the geology of relevance to geotechnical engineering within London. Unfortunately, the basement beneath London is covered by Cretaceous and Tertiary sediments. It is cut by major faults linked to the compressive phases of the Hercynian and Alpine Orogenies and to the regional extension that occurred during the Mesozoic between these compressive events. Evidence is presented that movement on basement fractures beneath London played a major role in the distribution and deformation of sediments within the Basin, causing local folding and faulting significant to engineering works. Basement rocks are exposed in SW England where the type and orientation of these fractures (faults and joints) can be examined in outcrop. This study, complemented by seismic sections in the southern UK, enable the architecture of this fault network within the basement to be determined. Understanding the fracture system in the basement provides a basis for (i), interpreting the lateral facies variations of sediments in the Basin and hence provides a means for predicting from a ground investigation the likely presence, activity or influence on site of such structures at depth and (ii), understanding the extent of local, steeply inclined and sub-horizontal planar zones of shearing when encountered on site. Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/cc/london-basin

London Clay, which underlies the majority of Greater London, has a high shrink–swell potential that can result in damage to foundations and surface infrastructure due to seasonal expansion and contraction of the clay. Currently, surface movement as a result of shrink–swell is not monitored in London, meaning that the magnitude and cyclicity of these movements is poorly understood. Persistent Scatterer Interferometric (PSI) Synthetic Aperture Radar data provide high-precision line-of-sight displacement measurements at a high point density across urban areas, offering the possibility of routine shrink–swell monitoring across whole cities. To test this, PSI data derived from TerraSAR-X (TSX) observations for the period from May 2011 to April 2017 were analysed for shrink–swell patterns across three areas of London in Hammersmith, Muswell Hill and Islington. A consistent cyclicity and amplitude was detected at all sites and the number of cycles is comparable with those identified in rainfall data. The amplitude of these cycles is smaller than anticipated, most probably because of the resisting effect of roads and pavements. The Cranfield University Leakage Assessment from Corrosivity and Shrinkage (LEACS) database was used to subdivide the PSI data and the average velocity and amplitude of each class statistically tested for significant differences between classes. The results show that it is not possible to statistically isolate possible soil shrink–swell movement in TSX PSI data in London. Thematic collection: This article is part of the ‘Measurement and monitoring’ collection available at: https://www.lyellcollection.org/cc/measurement-and-monitoring

The Eocene Harwich Formation, underlying the Greater London (UK) area, presents many construction problems for design and location of tunnels, pipelines and other engineering infrastructure projects. Variable deposits make up the sequence of the Harwich Formation. These include cemented fault zones, hard grounds, loose gravel and sand that, when unexpectedly encountered, can cause construction delays and increase costs. Here, we interpret borehole cores and logs, and in situ observations coupled with borehole-derived samples, and calculate particle-size distributions to develop a general facies model that accounts for the lithological distribution within the Harwich Formation. This provides an improved geological framework for proposed subsurface construction that can reduce inherent engineering uncertainties, not only in the London region but potentially also in other similar geological environments.

In this paper, originally submitted in answer to ESA’s “Voyage 2050” call to shape the agency’s space science missions in the 2035–2050 timeframe, we emphasize the importance of a Venus exploration programme for the wider goal of understanding the diversity and evolution of habitable planets. Comparing the interior, surface, and atmosphere evolution of Earth, Mars, and Venus is essential to understanding what processes determined habitability of our own planet and Earth-like planets everywhere. This is particularly true in an era where we expect thousands, and then millions, of terrestrial exoplanets to be discovered. Earth and Mars have already dedicated exploration programmes, but our understanding of Venus, particularly of its geology and its history, lags behind. Multiple exploration vehicles will be needed to characterize Venus’ richly varied interior, surface, atmosphere and magnetosphere environments. Between now and 2050 we recommend that ESA launch at least two M-class missions to Venus (in order of priority): a geophysics-focussed orbiter (the currently proposed M5 EnVision orbiter – [1] – or equivalent); and an in situ atmospheric mission (such as the M3 EVE balloon mission – [2]). An in situ and orbital mission could be combined in a single L-class mission, as was argued in responses to the call for L2/L3 themes [3–5]. After these two missions, further priorities include a surface lander demonstrating the high-temperature technologies needed for extended surface missions; and/or a further orbiter with follow-up high-resolution surface radar imaging, and atmospheric and/or ionospheric investigations.

Fluvial erosion is usually assumed to be absent on Venus, precluded by a high surface temperature of ~450 °C and supported by extensive uneroded volcanic flows. However, recent global circulation models suggest the possibility of Earth-like climatic conditions on Venus for much of its earlier history, prior to catastrophic runaway greenhouse warming. We observe that the stratigraphically oldest, geologically most complex units, tesserae, exhibit valley patterns morphologically similar to the patterns resulting from fluvial erosion on Earth. Given poor topographic resolution, we use an indirect technique to recognize valleys, based on the pattern of lava flooding of tesserae margins by adjacent plains volcanism. These observed valley patterns are attributed to primary geology, tectonic deformation, followed by fluvial erosion (and lesser wind erosion). This proposed fluvial erosion in tesserae provides support for climate models for a cool, wet climate on early Venus and could be an attractive research theme for future Venus missions., The authors here use Magellan data to interpret geomorphological features on Venus and present a strong hypothesis for fluvial erosion.

A methodology for the remotely sensed monitoring, measurement and quantification of littoral zone platform downwearing has been developed and is demonstrated, using Persistent Scatterer Interferometric Synthetic Aperture Radar data and analysis. The research area is a 30 km section of coast in East Sussex, UK. This area combines a range of coastal environments and is characterised by the exposure of chalk along the cliffs and coastal platform. Persistent Scatterer Interferometry (PSI) has been employed, using 3.5 years of Sentinel-1 SAR data. The results demonstrate an average ground level change of −0.36 mm a−1 across the research area, caused by platform downwearing. Protected sections of coast are downwearing at an average of −0.33 mm a−1 compared to unprotected sections, which are downwearing more rapidly at an average rate of −1.10 mm a−1. The material properties of the chalk formations in the platform were considered, and in unprotected areas the weakest chalk types eroded at higher rates (−0.66 mm a−1) than the more resistant formations (−0.53 mm a−1). At a local scale, results were achieved in three studies to demonstrate variations between urban and rural environments. Individual persistent scatterer point values provided a near-continuous sequence of measurements, which allowed the effects of processes to be evaluated. The results of this investigation show an effective way of retrospective and ongoing monitoring of platform downwearing, erosion and other littoral zone processes, at regional, local and point-specific scales.

The near-surface of London is faulted, although the locations, architecture and tectonic origins of the faults are broadly unknown. This presents serious issues for geotechnical engineering in London and has implications for our structural understanding of the London Basin. The region is a product of Alpine compression, yet it is unclear whether these major faults are new Alpine shears or reactivated basement faults. We assess the plausibility of Alpine reactivation and inheritance of basement faults in London through three investigations: analysing structures in the near-surface; mechanically assessing the feasibility of basement fault reactivation under Alpine stress conditions; and comparing inheritance mechanisms with observations in London and the Thames Estuary. Three major en echelon fault sets are identified. These appear to have compartmentalized London9s near-surface geology and are all interpreted to be products of Alpine reactivation of the underlying basement faults. Fault interaction and linkage is evidenced by complex zones of intense faulting identified by tunnelling projects. The role of new structural development in accommodating Alpine compression is considered to have been comparatively minor. The lack of major faulting in the basin9s interior may reflect the competence of the underlying Anglo–Brabant Massif in restricting Alpine strains to its margins. Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/cc/london-basin

The Lee Tunnel was constructed as the first part of the Thames Tideway Improvement scheme, between 2010 and 2016. With tunnelling for the East section of the main Thames Tideway Tunnel, which joins the Lee Tunnel at Abbey Mills Pumping Station, beginning in early 2020, this paper investigates patterns of deformation in East London during construction of the Lee Tunnel. An unexpected geological feature, later identified as a drift filled hollow, was discovered during tunnelling. This study demonstrates that had eight years of ERS Persistent Scatterer Interferometry (PSI) data been analysed prior to tunnelling, the unusual pattern of displacement may have been recognised and further targeted borehole investigations taken place before the launch of the tunnel boring machine. Results also show how areas of different land use, including cemeteries and historic landfill, exhibit differences in settlement behaviour, compared with surrounding terraced housing. This research highlights the challenges in interpreting PSI results in an urban area with ongoing construction and the value of a long archive of data, which now spans almost three decades in London, that can be used to establish a baseline prior to construction.

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 Earth have been a privileged target of the world's leading space agencies. EnVision is a mission proposal designed for Venus and competing for ESA's next launch opportunity with the objective of studying Earth's closest neighbor. The main goal is to study geological and atmospheric processes, namely surface processes, interior dynamics and atmosphere, to determine the reasons behind Venus and Earth's radically different evolution despite the planets' similarities. To achieve these goals, the operational orbit selection is a fundamental element of the mission design process. The design of an orbit around Venus faces specific challenges, such as the impossibility of choosing Sun-synchronous orbits. In this paper, an innovative genetic algorithm optimization was applied to select the optimal orbit based on the parameters with more influence in the mission planning, in particular the mission duration and the coverage of sites of interest on the Venusian surface. The solution obtained is a near-polar circular orbit with an altitude of 259 km that enables the coverage of all priority targets almost two times faster than with the parameters considered before this study.

This paper describes and discusses the various elements of a one-week Engineering Geology field trip that has been developed for second-year undergraduate students studying Civil Engineering at Imperial College London. It is an essential component of the education of civil engineers and, as such, is a requirement of the accreditation defined by the Institution of Civil Engineers Joint Board of Moderators (ICE JBM). The trip is structured to develop the students9 awareness of geological features and their ability to record and sketch key observations in the field. Having described the geological features, the students are prompted to think about consequent potential engineering hazards relating to them and also the influence of human activity, past and present, on the ground and environment. During the course of the week the students develop their observational and logging skills, with constant staff feedback both outdoors and during summary student presentation sessions in the evenings. A marked progressive improvement has been noted as a consequence of this approach. On the final day of the week the students have to map a coastal section, observing and recording the stratigraphy and significant features such as bedding, discontinuities and faulting, with the latter quantified by measuring quantities such as dip, strike and plunge, as appropriate. The students9 work, assessed as part of the field trip, is completed by them and handed in just before final departure at the end of the week, most of it being completed in the field.

The Limmo Peninsula site has some of the most complex geology of London9s Crossrail project and was the launching point for four tunnel boring machines (TBMs) to allow construction of Crossrail9s eastern running tunnels. It is located in East London, c. 2 km east of the Canary Wharf business district, adjacent to the River Lea. It consists of a ventilation shaft, an auxiliary shaft, two sprayed concrete lining (SCL) tunnels interconnecting the shafts and four SCL adits for assisting in the launching of the TBMs. As part of the design requirements, some geological formations had to be depressurized from surface wells. The site is geologically complex: it is in the vicinity of a drift-filled hollow and it is located within the area of influence of several tectonic features. A geological ground model developed from important new information obtained during the design stage ground investigations and from direct observations conducted during construction stages reveals an inverted transtensional flower structure (i.e. it is now a transpressional restraining bend). Of special interest are the unusually low values of undrained shear strength of the London Clay associated with the tectonic setting.

Venus should be the most Earth-like of all our planetary neighbours: its size, bulk composition and distance from the Sun are very similar to those of Earth. How and why did it all go wrong for Venus? What lessons can be learned about the life story of terrestrial planets in general, in this era of discovery of Earth-like exoplanets? Were the radically different evolutionary paths of Earth and Venus driven solely by distance from the Sun, or do internal dynamics, geological activity, volcanic outgassing and weathering also play an important part? EnVision is a proposed ESA Medium class mission designed to take Earth Observation technology to Venus to measure its current rate of geological activity, determine its geological history, and the origin and maintenance of its hostile atmosphere, to understand how Venus and Earth could have evolved so differently. EnVision will carry three instruments: the Venus Emission Mapper (VEM); the Subsurface Radar Sounder (SRS); and VenSAR, a world-leading European phased array synthetic aperture radar that is the subject of this article. VenSAR will obtain images at a range of spatial resolutions from 30 m regional coverage to 1 m images of selected areas; an improvement of two orders of magnitude on Magellan images; measure topography at 15 m resolution vertical and 60 m spatially from stereo and InSAR data; detect cm-scale change through differential InSAR, to characterise volcanic and tectonic activity, and estimate rates of weathering and surface alteration; and characterise of surface mechanical properties and weathering through multi-polar radar data. These data will be directly comparable with Earth Observation radar data, giving geoscientists unique access to an Earth-sized planet that has evolved on a radically different path to our own, offering new insights on the Earth-sized exoplanets across the galaxy.

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, 144°E, here referred to as Scathach Fluctus, displays a number of morphological characteristics consistent with a pyroclastic flow deposit. These characteristics, particularly its lack of channelisation 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 km3 and 875 km3 but this may have been emplaced in more than one event. Interaction between Scathach Fluctus and a small volcanic cone constrain the flow velocity to 48 m s−1 and plausible volatile concentrations to at least 1·8 wt% H2O, 4·3 wt% CO2 or 6·1 wt% SO2, the latter two implying magma 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 recognised to date, and suggesting both a relatively volatile-rich mantle and a volcanic source for atmospheric SO2.

Air at high pressure has recently been encountered during ground investigation borehole drilling for the Thames Tideway project in London. The air was released from within the Upnor Formation (at the base of the Lambeth Group beds), which is at the top of the Lower Aquifer. Cavitation within the granular beds of the Lower Aquifer would have occurred as a consequence of drawdown from the extensive water extraction that began at the start of the nineteenth century, resulting in the water table dropping by almost 70 m. Estimated historical pore pressure profiles are postulated and the cavitation process that occurred, along with the subsequent pressurization of the air during recharge that has occurred in recent years, are discussed using behavioural concepts from unsaturated soil mechanics. The hypotheses are corroborated by a series of simple column experiments where the processes are modelled using analogous soils. Engineering implications of the presence of the pressurized air are discussed: besides the potential for borehole blow-out, another serious consideration is the depletion of oxygen from the trapped air by chemical reaction with the soil, increasing the risk of confined space hypoxia.

Deoxygenated air poses a serious, life-threatening hazard (confined space hypoxia) for engineering projects in London, particularly within the Upnor Formation of the Lambeth Group. This paper reviews its causes and postulates that it was induced by regional-scale dewatering and drawdown of the Lower Aquifer during the industrial growth of London, bringing air into contact with these sediments, which became oxidized. Ensuing post-industrial recharge and resaturation resulted in accumulations of often compressed deoxygenated air, trapped beneath overlying impermeable clay strata. Historically, glauconite has been considered to be the mineral most likely to remove oxygen from the trapped air, but it lacks potency as a reducing agent and remains unaltered in many oxidized sediments. Pyrite and organic carbon are both plausible, but rare. Green rust, a mixed Fe(II) and Fe(III) layered double hydroxide, is more likely, as it rapidly oxidizes on contact with air and is only briefly observed in fresh core samples. Two key ground engineering hazards are, therefore, identified: the misidentification of risk by reliance on observations of glauconite; and the likelihood of encountering pressurized deoxygenated air within Lambeth Group sediments in underground projects following short- or long-term changes in the groundwater level.

EnVision is an ambitious but low-risk response to ESA's call for a medium-size mission opportunity for a launch in 2022. Venus is the planet most similar to Earth in mass, bulk properties and orbital distance, but has evolved to become extremely hostile to life. EnVision's 5-year mission objectives are to determine the nature of and rate of change caused by geological and atmospheric processes, to distinguish between competing theories about its evolution and to help predict the habitability of extrasolar planets. Three instrument suites will address specific surface, atmosphere and ionosphere science goals. The Surface Science Suite consists of a 2.2 m 2 radar antenna with Interferometer, Radiometer and Altimeter operating modes, supported by a complementary IR surface emissivity mapper and an advanced accelerometer for orbit control and gravity mapping. This suite will determine topographic changes caused by volcanic, tectonic and atmospheric processes at rates as low as 1 mm a -1. The Atmosphere Science Suite consists of a Doppler LIDAR for cloud top altitude, wind speed and mesospheric structure mapping, complemented by IR and UV spectrometers and a spectrophotopolarimeter, all designed to map the dynamic features and compositions of the clouds and middle atmosphere to identify the effects of volcanic and solar processes. The Ionosphere Science Suite uses a double Langmiur probe and vector magnetometer to understand the behaviour and long-term evolution of the ionosphere and induced magnetosphere. The suite also includes an interplanetary particle analyser to determine the delivery rate of water and other components to the atmosphere. © 2011 Springer Science+Business Media B.V.

We present a structural analysis of an area of Venus’ surface centred on 3°S, 116°E. The area is dominated by a wide zone of deformation striking 050°N, distinguished from the terrain on either side of it by markedly different structural and morphological characteristics. The deformation zone contains two principal fault sets defined by form, position and orientation. Members of the first set are present along the length of the deformation zone. They are discontinuous, consistently right-stepping, and are interpreted as Riedel shears in a sinistral strike-slip regime. Members of the second fault set are interpreted as normal faults and are often seen in pairs forming extensional grabens. These faults are most prominent in the central region of the deformation zone, and coincide with a deflection in strike of both the first fault set and the boundaries of the deformation zone. A detailed kinematic analysis of all fault orientations and the boundaries of the deformation zone fit the predictions of transtensional theory, supporting the hypothesis that this sinistral strike-slip zone contains an extensional jog. This interpretation is further supported by analysis of the interaction between faults belonging to the two sets. Variation in intercept geometry, kinematic linking of the two fault sets, and rotation of fault strike between the two fault sets all strongly suggest simultaneous development of these structures, and therefore a common tectonic origin. A driving mechanism for such large-scale horizontal deformation on Venus has yet to be established.

Unexpected ground conditions are responsible for a number of engineering problems and hazards across London. A major reason for the unexpected nature of these events is the historical proprietary approach to site investigation, which has restricted knowledge transfer and inhibited the development of a London-wide geological context. Recent changes mean that much of these data are now accessible in the public domain for site investigation and useful in predicting the engineering hazards resulting from complex and variable geology. We advocate applying predictive 4D modelling to better constrain geological structures, facies, fissures and groundwater flow, and adopting an iterative approach that both informs local site models and updates the regional context. Reverse normal faulting, indicative of basin inversion, pull-apart structures and periglacial scour/pingo features are identified in a pilot study regional model. Applying this model to a small site investigation predicted otherwise unexpected faulting, generating horizontal fissuring that causes water to flow along the length of the fault system. Widely adopting this approach in London and other urban areas may substantially reduce the risk of unexpected ground hazards.

[1] The similar meander geometries of Venusian canali and terrestrial rivers imply that the in-channel flow regimes may be comparable. This work details meander geometry measurements from ten lowland canali and compares the extensive data set produced to a variety of solar system channels. The meander properties of Venusian canali do not closely match any channel so far observed on the terrestrial planets. However, analysis of the relationship between meander wavelength and radius of channel curvature confirms previous suggestions that the canali were carved by a low (water-like) viscosity fluid. Whether the canali are due to thermal and/or mechanical erosion of the plains by an exotic lava, or have some other genesis, the dominant meander wavelengths of 11 to 77 km require peak fluid discharge rates of up to 6.6 × 106 m3 s−1, an order of magnitude larger than terrestrial rivers. Slight decrease in width along the channel length was observed in most investigated canali, perhaps reflecting the effect of downstream loss processes. Cyclical variations in the average channel width were observed in some channels; where topographic data are available, these variations apparently correlate with peaks in plains topography. This indicates that the canali remained active, after their initially rapid formation, long enough to interact with the early stages of plains tectonism.

[1] High-resolution digital elevation models (DEMs) derived from Magellan Left-Left Stereo synthetic aperture radar data of Venus for a set of impact craters ranging in rim diameter from 5 to 300 km exhibit depths broadly as expected from theory but with significant departures for both large and small craters. In craters larger than 38 km diameter, rim-floor depth becomes independent of diameter with a mean of about 900 m. Most craters smaller than 18 km diameter are also found to be unexpectedly shallow. We discuss the accuracy and principal sources of error in our DEMs and conclude that this shallowness is real. This shallowness of small craters shows that midsize bolides (200–1000 m diameter) fragment in Venus' atmosphere and disperse over an area 10 to 20 times the original bolide diameter. We identify these craters as a new class of impact feature, the Compound Crater, which may correspond to the Knobby Base morphological class defined by others.

The population of London is around 7 million. The infrastructure to support this makes London one of the most intensively investigated areas of upper crust. However construction work in London continues to reveal the presence of unexpected ground conditions. These have been discovered in isolation and often recorded with no further work to explain them. There is a scientific, industrial and commercial need to refine the geological framework for London and its surrounding area. This paper reviews the geological setting of London as it is understood at present, and outlines the issues that current research is attempting to resolve.

Venus is physically similar to Earth but with no oceans and a hot dense atmosphere. Its near-random distribution of impact craters led to the inferences of episodic global resurfacing and a stagnant lid regime, and imply that it is not currently able to lose proportionately as much heat as Earth. This paper shows that a CO2-induced asthenosphere and decoupling of the mantle lid from the crust, caused by the elevated surface temperature, enables lid rejuvenation. Global hypsography implies a rate of 4·0±0·5 km² a−1 and an implied heat loss rate of 32·8±3·6 TW, ~90% of a scaled Earth-like rate of heat loss of 36 TW. Estimates of the rate of lid rejuvenation by plume activity – 0·07 to 0·09 km² a−1– imply that ten times the number of observed plumes are required to equal this rate of heat loss. However, lid rejuvenation by convection allows Venus to maintain a stable tectonic regime, with subcrustal horizontal extension (half-spreading) rates of between 25 and 50 mm a−1 determined from fits to topographic profiles across the principal rift systems. While the surface is largely detached from these processes, the association of rifting and other processes does imply that Venus is geologically active at the present day.