Variability in infragravity wave processes during estuary artificial entrance openings

Intermittently open/closed estuaries (IOCE) are wave-dominated estuaries with entrances that temporarily close to the ocean. Wave–current interactions play a major role in estuary entrance morphodynamics and influence the degree of energy transfer from the ocean into the lagoon. This study utilizes artificial entrance openings of multiple ICOE in Victoria, Australia, to capture continuous hydrodynamic and geomorphic data throughout the opening cycle. We illustrate that water level oscillations in the infragravity (IG) band) are present in the basin during open entrance conditions. IG waves were observed to propagate up to 1.8 km upstream of the mouth while the entrance was open. Our work identifies that changes in cross-sectional area, bed depth at the berm position, and offshore wave height control the magnitude of IG waves within the estuary basin. IG wave magnitude is also tidally modulated and increases with high tides when the nearshore water level is higher. Late during the drainage phase, waves were observed to track the margins of the channel, away from the thalweg, and reach the basin. IG wave energy was highest immediately after the basin had ceased draining and while channel dimensions at the mouth were within 10% of their maximum value. As the entrance aggrades, IG wave magnitude decreases in the absence of energetic offshore wave conditions. We relate the changes in IG wave magnitude and frequency to a six-stage conceptual model of the opening–closure sequence. Within the basin, IG wave energy, height and frequency were also consistently highest closer to the mouth and decreased with distance upstream. Our findings indicate that water level oscillations in the IG band are a persistent feature in IOCE and may be the norm rather than the exception in these systems. As IG waves were captured serendipitously as part of a larger field campaign, future work will focus on instrumenting IOCE to gain high-resolution data to quantify IG wave processes during entrance openings. © 2020 John Wiley & Sons, Ltd.     

Seismic hybrid simulation of a nonductile RC building with severe damage to multiple columns

Reinforced concrete frame structures built prior to the mid‐1970s are susceptible to brittle column failure under seismic action, potentially leading to progressive collapse of the structure. The behavior of columns susceptible to brittle shear‐axial failure has been studied previously but rarely has the interaction between damaged columns and the surrounding three‐dimensional structure been investigated experimentally and at full scale. In this study, as the second in a series of hybrid simulations, two full‐scale reinforced concrete columns of a representative pre‐1970s structure were tested at the Multi‐axial Full‐scale Substructure Testing and Simulation (MUST‐SIM) laboratory. Through the use of hybrid simulation, the interaction of the columns with the surrounding structure is studied under a severe seismic motion including vertical excitation. The computational model representing the remainder of the representative 10‐story structure is created in the computer program OpenSees. During the hybrid simulation, both physical specimens experience significant loss of shear and axial strength, and the effects of these failures on the surrounding system are described. The three‐dimensional computational model in OpenSees allowed for analytical flexural‐axial failure of a third column in the structure to occur. The effects of these multiple failures on the response of a full structural system under seismic action are quantified, and the progressive collapse resistance mechanisms are discussed. Copyright © 2016 John Wiley & Sons, Ltd.     

High‐pressure metamorphic mineralogy of the Martian crust with implications for density and seismic profiles

Here, we calculate the mineralogy of the Martian lower crust and upper mantle as a function of pressure and temperature with depth using four bulk compositions (average crust, Gusev basalt, olivine‐phyric shergottite, and primitive average mantle). We then use this mineralogy to extract rock properties such as density and seismic velocities, describe their changes with varying conditions and geotherms, and make predictions for the crust–mantle boundary. Mineralogically, all compositions produce garnet, orthopyroxene, clinopyroxene in varying proportions at high pressures, with differences in minor minerals (spinel, ilmenite, rutile, and/or K‐feldspar). According to our calculations, the average crust and Gusev basalt compositions have the potential to yield higher densities than the average mantle composition, particularly for thicker crusts and/or colder geotherms. Therefore, recycling of the Martian crust into the mantle could occur through the process of crustal delamination, if not kinetically inhibited. However, our results show that, depending on crustal thickness, the crust may not be easily distinguishable from the mantle in seismic properties.     

Sedimentological and petrographic analysis of drill core FC77-1 from the flank of the central uplift,Flynn Creek impact structure,Tennessee

Drill core FC77-1 on the flank of the central uplift, Flynn Creek impact structure, Tennessee, contains 175 m of impact breccia lying upon uplifted Lower Paleozoic carbonate target stratigraphy. Sedimentological analysis of this 175-m interval carbonate breccia shows that there are three distinct sedimentological units. In stratigraphic order, unit 1 (175–109 m) is an overall coarsening-upward section, whereas the overlying unit 2 (109–32 m) is overall fining-upward. Unit 3 (32–0 m) is a coarsening-upward sequence that is truncated at the top by postimpact erosion. Units 1 and 3 are interpreted as debris or rock avalanches into finer sedimentary deposits within intracrater marine waters, thus producing progressively coarser, coarsening-upward sequences. Unit 2 is interpreted to have formed by debris or rock avalanches into standing marine waters, thus forming sequential fining-upward deposits. Line-logging of clasts ranging from 5 mm to 1.6 m, and thin-section analysis of selected drill core samples (including clasts < 5 mm), both show that the Flynn Creek impact breccia consists almost entirely of dolostone clasts (90%), with minor components of cryptocrystalline melt clasts, chert and shale fragments, and clastic grains. Cryptocrystalline melt clasts, which appear isotropic in thin section, are in fact made of exceedingly fine quartz crystals that exhibit micro-Fourier transform infrared (FTIR) and micro-Raman spectra consistent with crystalline quartz. These cryptocrystalline melt clasts are the first melt clasts of any kind to be reported from Flynn Creek impact structure.     

Risk and trust in the cultural industries

Preliminary claims have been made that working practices within cultural industries such as fashion, music, design and the night time economy may differ from Fordist or modernist arrangements. Cultural firms are often imagined to be more innovative, information-rich, dynamic, flexible, non-hierarchical and dependent on local clusters and networks than their Fordist counterparts (Lash and Urry, 1994). As their impact and significance increase, understanding how creative and cultural industries actually work is of high priority. This paper presents preliminary findings from an on-going ESRC funded study of cultural Micro and Small Enterprises (MSEs) within Manchester, England. Drawing on one element of the project, this paper considers the significance of risk and the importance of social trust for the cultural entrepreneur. Following a discussion of Beck’s development of risk as an analytical concept, and its intersection with Giddens’ notion of ‘active trust’, the paper examines how risk and trust are defined, experienced and negotiated by entrepreneurs in Manchester’s cultural industries. It is suggested that senses of risk are constitutive and often pivotal to the whole economic and social basis of cultural entrepreneurship – risk being central to choices made not only in business but in the lifeworld more generally. The paper then investigates the importance of trust for facilitating as well as countering or offsetting risk. Empirical evidence is presented to show how risk and trust co-relate and interact as constitutive elements within a wider set of shifting relationships between work, leisure and lifestyle in the ‘creative city’.     

Assimilation of preexisting Pleistocene intrusions at Long Valley by periodic magma recharge accelerates rhyolite generation: rethinking the remelting model

Rhyolite flows and tuffs from the Long Valley area of California, which were erupted over a two-million-year time period, exhibit systematic trends in Nd, Hf, and Pb isotopes, trace element composition, erupted volume, and inferred magma residence time that provide evidence for a new model for the production of large volumes of silica-rich magma. Key constraints come from geochronology of zircon crystal populations combined with a refined eruption chronology from Ar–Ar geochronology; together these data give better estimates of magma residence time that can be evaluated in the context of changing magma compositions. Here, we report Hf, Nd, and Sr isotopes, major and trace element compositions, ⁴⁰Ar/³⁹Ar ages, and U–Pb zircon ages that combined with existing data suggest that the chronology and geochemistry of Long Valley rhyolites can be explained by a dynamic interaction of crustal and mantle-derived magma. The large volume Bishop Tuff represents the culmination of a period of increased mantle-derived magma input to the Long Valley volcanic system; the effect of this input continued into earliest postcaldera time. As the postcaldera evolution of the system continued, new and less primitive crustal-derived magmas dominated the system. A mixture of varying amounts of more mafic mantle-derived and felsic crustal-derived magmas with recently crystallized granitic plutonic materials offers the best explanation for the observed chronology, secular shifts in Hf and Nd isotopes, and the apparently low zircon crystallization and saturation temperatures as compared to Fe–Ti oxide eruption temperatures. This scenario in which transient crustal magma bodies remained molten for varying time periods, fed eruptions before solidification, and were then remelted by fresh recharge provides a realistic conceptual framework that can explain the isotopic and geochemical evidence. General relationships between crustal residence times and magma sources are that: (1) precaldera rhyolites had long crustal magma residence times and high crustal affinity, (2) the caldera-related Bishop Tuff and early postcaldera rhyolites have lower crustal affinity and short magma residence times, and (3) later postcaldera rhyolites again have stronger crustal signatures and longer magma residence times.     

Geochronological constraints on Caledonian strike–slip displacement in Svalbard,with implications for the evolution of the Arctic

The timing of Svalbard's assembly in relation to the mid‐Paleozoic Caledonian collision between Baltica and Laurentia remains contentious. The Svalbard archipelago consists of three basement provinces bounded by N–S‐trending strike–slip faults whose displacement histories are poorly understood. Here, we report microstructural and mineral chemistry data integrated with ⁴⁰Ar/³⁹Ar muscovite geochronology from the sinistral Vimsodden‐Kosibapasset Shear Zone (VKSZ, southwest Svalbard) and explore its relationship to adjacent structures and regional deformation within the circum‐Arctic. Our results indicate that strike–slip displacement along the VKSZ occurred in late Silurian–Early Devonian and was contemporaneous with the beginning of the main phase of continental collision in Greenland and Scandinavia and the onset of syn‐orogenic sedimentation in Silurian–Devonian fault‐controlled basins in northern Svalbard. These new‐age constraints highlight possible links between escape tectonics in the Caledonian orogen and mid‐Paleozoic terrane transfer across the northern margin of Laurentia.     

In-Street Wind Direction Variability in the Vicinity of a Busy Intersection in Central London

We present results from fast-response wind measurements within and above a busy intersection between two street canyons (Marylebone Road and Gloucester Place) in Westminster, London taken as part of the DAPPLE (Dispersion of Air Pollution and Penetration into the Local Environment; www.dapple.org.uk ) 2007 field campaign. The data reported here were collected using ultrasonic anemometers on the roof-top of a building adjacent to the intersection and at two heights on a pair of lamp-posts on opposite sides of the intersection. Site characteristics, data analysis and the variation of intersection flow with the above-roof wind direction (θ _ref ) are discussed. Evidence of both flow channelling and recirculation was identified within the canyon, only a few metres from the intersection for along-street and across-street roof-top winds respectively. Results also indicate that for oblique roof-top flows, the intersection flow is a complex combination of bifurcated channelled flows, recirculation and corner vortices. Asymmetries in local building geometry around the intersection and small changes in the background wind direction (changes in 15- min mean θ _ref of 5°–10°) were also observed to have profound influences on the behaviour of intersection flow patterns. Consequently, short time-scale variability in the background flow direction can lead to highly scattered in-street mean flow angles masking the true multi-modal features of the flow and thus further complicating modelling challenges.     

Recent geological and hydrological activity on Mars: The Tharsis/Elysium corridor

The paradigm of an ancient warm, wet, and dynamically active Mars, which transitioned into a cold, dry, and internally dead planet, has persisted up until recently despite published Viking-based geologic maps that indicate geologic and hydrologic activity extending into the Late Amazonian epoch. This paradigm is shifting to a water-enriched planet, which may still exhibit internal activity, based on a collection of geologic, hydrologic, topographic, chemical, and elemental evidences obtained by the Viking, Mars Global Surveyor (MGS), Mars Odyssey (MO), Mars Exploration Rovers (MER), and Mars Express (MEx) missions. The evidence includes: (1) stratigraphically young rock materials such as pristine lava flows with few, if any, superposed impact craters; (2) tectonic features that cut stratigraphically young materials; (3) features with possible aqueous origin such as structurally controlled channels that dissect stratigraphically young materials and anastomosing-patterned slope streaks on hillslopes; (4) spatially varying elemental abundances for such elements as hydrogen (H) and chlorine (Cl) recorded in rock materials up to 0.33 m depth; and (5) regions of elevated atmospheric methane. This evidence is pronounced in parts of Tharsis, Elysium, and the region that straddles the two volcanic provinces, collectively referred to here as the Tharsis/Elysium corridor. Based in part on field investigations of Solfatara Crater, Italy, recommended as a suitable terrestrial analog, the Tharsis/Elysium corridor should be considered a prime target for Mars Reconnaissance Orbiter (MRO) investigations and future science-driven exploration to investigate whether Mars is internally and hydrologically active at the present time, and whether the persistence of this activity has resulted in biologic activity.     

Comparison of radar and gauge precipitation data in watershed models across varying spatial and temporal scales

Precipitation is a key control on watershed hydrologic modelling output, with errors in rainfall propagating through subsequent stages of water quantity and quality analysis. Most watershed models incorporate precipitation data from rain gauges; higher‐resolution data sources are available, but they are associated with greater computational requirements and expertise. Here, we investigate whether the Multisensor Precipitation Estimator (MPE or Stage IV Next‐Generation Radar) data improve the accuracy of streamflow simulations using the Soil and Water Assessment Tool (SWAT), compared with rain gauge data. Simulated flows from 2002 to 2010 at five timesteps were compared with observed flows for four nested subwatersheds of the Neuse River basin in North Carolina (21‐, 203‐, 2979‐, and 10 100‐km² watershed area), using a multi‐objective function, informal likelihood‐weighted calibration approach. Across watersheds and timesteps, total gauge precipitation was greater than radar precipitation, but radar data showed a conditional bias of higher rainfall estimates during large events (>25–50 mm/day). Model parameterization differed between calibrations with the two datasets, despite the fact that all watershed characteristics were the same across simulation scenarios. This underscores the importance of linking calibration parameters to realistic processes. SWAT simulations with both datasets underestimated median and low flows, whereas radar‐based simulations were more accurate than gauge‐based simulations for high flows. At coarser timesteps, differences were less pronounced. Our results suggest that modelling efforts in watersheds with poor rain gauge coverage can be improved with MPE radar data, especially at short timesteps. Published 2013. This article is a U.S. Government work and is in the public domain in the USA.