Rheological and petrological implications for a stagnant lid regime on Venus

AbstractVenus 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±0·5km²a−1 and an implied heat loss rate of 32·8±3·6TW, ~90% of a scaled Earth-like rate of heat loss of 36TW. Estimates of the rate of lid rejuvenation by plume activity – 0·07 to 0·09km²a−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 50mma−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

Development of an Engineering Geology field trip for Civil Engineering students

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 ICE JBM. The trip is structured to develop the students’ 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 students’ 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

VenSAR: A multi-functional S-band radar for the EnVision mission to Venus

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

The geological context and evidence for incipient inversion of the London Basin

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 ex-plain 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

A novel orbiter mission concept for venus with the envision proposal

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 with the objective of studying Earth’s closest neighbor. Designed for Venus and competing for ESA’s next launch opportunity, the proposal already went through the selective technical review for the M4 launch opportunity, and was submitted to the M5 call, incorporating feedback from ESA. 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. After summarizing the EnVision proposal’s mission concept for Venus, the optimization and innovation of the operational orbit design will be analyzed in terms of its benefits to the mission

Monitoring Littoral Platform Downwearing using Differential SAR Interferometry

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

Engineering geology and tunnelling in the Limmo Peninsula, East London

The Limmo Peninsula site has some of the most complex geology of London's Crossrail project and was the launching point for four tunnel boring machines (TBMs) to allow construction of Crossrail's 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