Passage Zone Research Articles

NUMERICAL MODELING OF THE PROCESS OF DEGRADATION OF PERMAFROST SOILS OF THE BASE OF THE RAILWAY ROADBED IN THE AREA OF PASSAGE OF CONSTRUCTION EQUIPMENT

When studying freezing, permafrost and thawing soils, it is absolutely necessary to develop models of processes occurring in soils and their mathematical description as a basis. This will make it possible to perform a calculated assessment of the "thawing foundation - structure" system during the entire lifetime of the object, which will make it possible to design it correctly. The article considers a soil model that allows us to consider the process of degradation of permafrost soils of the base of the railway roadbed in the zone of passage of construction equipment.

Doğu Akdeniz geçit kuşağında farklı pazar tipi yerfıstıklarının (Arachis hypogaea L.) ikinci ürün yetitiriciliğinde bazı kalite ve özelliklerinin belirlenmesi

This study was carried out in Osmaniye location of Oil Seed Research Institute in 2020-2021 in order to determine some yield and quality characteristics in second crop cultivation of peanuts with different market types in the Eastern Mediterranean transition zone. Eleven different genotypes of Runner (Georgia Green) Virginia (NC 7, Masal, Halisbey, Wilson, Çom, Brantley, Sultan, Düziçi 1) Spanish (Florispan, Nigeria 1) types of peanut were used in the study. In the study, number of pods per plant, 1st quality pod ratio, pod weight per plant, 100 pod and seed weight, shelling percentage, pod yield, oil content and, protein content parameters were investigated. The number of pods per plant is between 20.8 (Nigeria 1) and 51.4 (Düziçi 1); pod weight per plant varied between between 12.3 g (Nigeria-1) and 64.9 g (Halisbey). It was determined that 100 pod weight and 100 seed weights varied between 66.8-289.0 g and 29.6-106.5 g, respectively. Pod yield varied between 1963 kg ha-1 (Nigeria 1) and 4846 kg ha-1 (Düziçi 1). As a result, it was determined that Düziçi 1 genotype, Brantley and Halisbey cultivars came to the fore in terms of the investigated characteristics in the Eastern Mediterranean Passage zone. In the study, while the second crop peanut variety suitable for the Eastern Mediterranean Transition zone was determined, the varieties to be used as breeding material were also determined.

Дослідження умов доцільності застосування подвоєних або потроєних шин колісних енергетичних засобів

Goal. To determine and justify the conditions under which the use of double/triple tires of wheeled energy vehicles instead of single ones will be appropriate. Methods. Theoretical studies were carried out using the basics of the theory of tractors and agricultural machines. The object of research was the MTZ1221 multipurpose-weed tractor, the front axle of which was studied in variants with single, double, and triple tires. Soil compaction in the passage zones of these tires was taken as an argument for the yield function of an agricultural crop (spring barley). Results. Calculations established that the intensity of reducing the depth of the wheel track, compacting the soil, and increasing the yield of the cultivated crop (spring barley) was higher when using a double tire compared to a single one, and lower in the case of replacing a double tire with a triple one. Due to the use of a triple tire instead of a single one, the depth of the created track was reduced. Conclusions. A new analytical dependence was obtained, which could be used when evaluating the feasibility of using doubled or tripled tires of wheeled energy vehicles to reduce their compacting effect on the soil and correspondingly increase the yield of cultivated crops. By evaluating the use of different numbers of front tires on the example of the MTZ1221 tractor, it was established that the intensity of reducing the depth of the wheel track, compacting the soil, and increasing the yield of the cultivated crop (spring barley) was higher for a double tire compared to a single tire, and lower in the case of replacing a double tire with a triple one. The use of a three-wheel tire instead of a single one led to a decrease in the depth of the created track by at least 30%, a decrease in soil compaction by 42%, and an increase in the yield of the cultivated crop by 2.2 times.

Energy loss of radial inflow turbine for organic Rankine cycle using mixture based on entropy production method

The radial inflow turbine is the core component of the organic Rankine cycle(ORC) system. Based on the internal flow field of the turbine analyzed by computational fluid dynamics (CFD), the energy dissipation of a radial inflow turbine with variable guide vane is determined by the entropy production analysis method. In the presented work, the mixture of R245fa/R134a is selected as the working fluid, and the effects of tip clearance and mixing ratio on the flow loss characteristics are investigated. The results show that the high entropy production region in the stator is caused by leakage vortex and shock phenomenon, while the passage vortex and leakage vortex are the reasons for the high loss area in the rotor. The total volume entropy production of rotor is mainly composed of the passage zone, which is significantly higher than that of the stator. As the tip clearance increases from 3% to 10%, the total entropy production of stator and rotor increases by 54.5 and 161.7% respectively, and the output power and isentropic efficiency of the turbine decrease by 14.7% and 14.6% respectively. With the increase of R245fa mass fraction, the total volume entropy production of the stator and rotor decreases linearly. Compared with R134a, the turbine isentropic efficiency of R245fa increases by 3.1%.

Gupeiite Body in the Siberian Taiga (the Zone of Passage of the Tunguska Meteorite and the Vitim Bollid)

Many years have passed since the two cosmic bodies of the Tunguska meteorite and the Vitim bollid fell to Earth, but so far the substance of these bodies has not been found on Earth. Therefore, each metal body found on the territory of their passage is of particular interest. The body of iron silicide weighing 12 kg was studied, which was accidentally discovered by a hunter of the village of Kyker in the Siberian taiga on the right bank of the Nercha River, Tungokochensky district, Trans-Baikal Territory. Coordinates of the place of discovery are: 53º19'N lat, 116º19'E long. The territory is located in the zone of the passage of the Tunguska meteorite and the Vitim bollid, 25 km from the hunting village of Green Lake. The body is named “Ilekta” after the nearest stream flowing into the Nercha River. The composition and magnetic properties of the exotic find have been determined. It is established that its main mass is composed of iron silicide, gupesiite Fe3Si (zussite?) and contains inclusions of needle-like rhabdite. On the surface, the body is covered with a melting crust, with signs of boiling, a bubbly structure and a film of clay minerals of terrestrial origin. In the molten porous crust, eutectic-schreibersite-gupeiite is observed, and rare titanium carbide crystals are also noted. The magnetic susceptibility of the samples is not uniform (286.6 - 461.8 10-6E-06 m3/kg). It is assumed that a drop of melt separated from the flying space body, and experienced overheating and boiling of the surface layer in the dense layers of the atmosphere.

Investigation the Services Provided to Disabled in Çanakkale

Every healthy person is a disabled candidate, which is why disabled people have an important place in our society and worldwide. However, our citizens with disabilities face many problems in society every day. In this study, some of the problems faced by disabled people and the efforts to remedy them were examined in terms of occupational health and safety. In the study, a survey of 60 questions was organized to be answered by disabled individuals residing in Çanakkale province. The survey, which was answered by 60 disabled individuals, was analyzed by Statistical Package for the Social Sciences (SPSS) 22.0. 44 (73.3 %) of the employees participating in the study are male, 24 (40 %) of them are between 36-45 years. Only 19 (31.7 %) of the participants have received higher education and higher education. 41 of the participants (68.3%) are working. Only 17 (41.5%) of the working participants work in the public sector. Of the participants, 23 (38.3%) were physical, 8 (13.4%) were mental, 7 (11.7%) were auditory, 2 (3.3%) had speech disorders, 2 (3.3%) had learning disabilities, 2 ' of them (3.3%) had visual impairment and 16 (26.7%) had disability in the other category. The data obtained focused on the safe passage zones for the disabled, sports field-sports guidance and the insufficiency of the disabled staff in public institutions. The identified problems can be solved by establishing a unit for the determination, analysis and follow-up of the services to be provided for disabled individuals within the municipality.

Englacial lake dynamics within a Pleistocene cordilleran ice sheet at Kima' Kho tuya (British Columbia, Canada)

Passage zones are stratigraphic surfaces found in littoral settings separating deposits diagnostic of subaqueous environments from overlying sequences of subaerial deposits. In glaciovolcanic settings, passage zone surfaces are unequivocal records of the heights and depths of paleo-englacial lakes at a specific point in time and space, thereby, informing on the presence and nature of the enclosing ice sheet. Kima' Kho, a Pleistocene glaciovolcano (i.e. tuya) located in the northern Cordillera of British Columbia, features multiple and diverse passage zones. The basaltic volcano comprises four main stratigraphic packages: i) subaqueously and subaerially deposited lapilli tuffs (Lt1/Lt2) forming a central tephra cone and representing an explosive onset to the eruption, ii) subaqueously deposited, steeply-inclined beds of tuff breccia dominated by pillow lava fragments (Tb1-3), iii) stacked sheets of subaerial pahoehoe lavas (L1-3), and iv) dykes and sills (I) intruding all units. Stratigraphic and geochemical relationships suggest that Kima' Kho volcanism was continuous and 40Ar/39Ar geochronometry on three samples yields a mean age of 1949 ± 63 ka. Three temporally distinct passage zones record the interplay between growth of the volcanic edifice, syn-volcanic melting of the enclosing ice sheet, and fluctuations in the depth of the englacial lake. The earliest passage zone (PZ1) is expressed in two different ways marking a transition from explosive to effusive eruption: (i) within pyroclastic deposits of the tephra cone (<1800 masl), and (ii) by pillow lava tuff breccia deposits overlain by subaerial lavas. Together they record a peak, sustained lake depth of 320–340 m that constrains the enclosing Cordilleran ice sheet to a minimum thickness of ∼400 m. Two subsequent passage zones (PZ2-3), also defined by sequences of subaerial lavas resting on dipping beds of pillow lava tuff breccias, occur at lower elevations: 1690-1640 masl and 1740-1720 masl, respectively. The latter two passage zones indicate a major draining of the englacial lake followed by refilling to depths of 230–180 m and 260–280 m, respectively. The substantial decline in lake level between PZ1 and PZ2 suggests a massive, catastrophic deluge (i.e. jökulhlaup) of 1–2 km3. Lastly, the reconstructed glaciovolcanic evolution of Kima' Kho demands the presence of a regionally extensive ice sheet overlying the Kawdy plateau at ∼1.9 Ma and representing an earlier incarnation of the Cordilleran Ice Sheet (CIS).

Exploration vectoring from the white mica spectral footprint in the atypical auriferous Lavra Velha deposit, San Francisco Craton, Brazil

The Lavra Velha deposit is a poorly understood gold deposit hosted by the 2.1 Ga Ibitiara Granitoid, within the São Francisco Craton (Brazil). Although not consensually agreed, Lavra Velha has been inserted into the Iron Oxide-Copper-Gold (IOCG) class. The major alteration footprint of the deposit involves an upward mineralogical zoning from widespread chlorite-epidote-calcite (propylitic) to white mica-hematite-quartz association with an intervening magnetite-tourmaline-quartz-white mica realm. The ore occurs mostly as massive lenses composed of magnetite, hematite, pyrite, tennantite, bismuthinite, digenite and native gold. Gold is present as inclusion within hematite, pyrite, quartz and cassiterite, in association with white mica, but also with supergene jarosite-goethite. The proximal footwall and hanging walls of the mineralization are commonly anomalous in Cr-Ni-Co and, where weathered, a talc-nontronite association is documented. Such features are considered to represent ultramafic rocks closely associated with mineralization. Reflectance spectroscopy results show that white mica, hematite and Fe-tourmaline are closely and spatially associated with gold mineralization, thus representing a proximal alteration mineralogy. Notably, white mica becomes progressively more phengitic (>2210 nm) as higher Au grades are laterally approached, whereas it has muscovitic composition (<2198 nm) where gold grades are waning. This chemical gradient can be used as an exploratory guide to find zones of higher-grade mineralization. The crystallinity of white mica reveals a strong zonation from the top to the bottom of the deposit defined by the downward variation from muscovite to illite. The passage zone from muscovite to illite represents potential sites for gold deposition. In weathered profiles, the spectral mapping of talc-nontronite would be key in detecting gold-related ultramafic rocks. This work found that SWIR hyperspectral measurement of white mica features provides an efficient means for vectoring to gold mineralization, at least to district scale. The unusual mineralogical signature of Lavra Velha is not diagnostic of any specific style of known deposit and further in-depth studies are required to decipher what kind of deposit it belongs.

Thermal Behavior in Cross-Passage Construction during Artificial Ground Freezing: Case of Harbin Metro Line

The successful construction of cross passages in water-rich sand strata requires the ground reinforcement of soil in passage zones. To address these conditions, artificial ground freezing was introduced, which is an innovative presupport technique that has been extensively applied in tunnel engineering. However, insufficient temperature monitoring data and complex numerical models have hindered accurate predictions of complete freezing curtains in engineering applications. In light of this, this paper proposes a heat–moisture coupling model to predict the dynamic formation of the freezing curtain. This was achieved by combining the heat transfer, Richards’s equation, and the Darcy equation for porous media. As a result, the hydraulic parameters could be obtained through nuclear magnetic resonance. The proposed numerical model was further validated through laboratory testing by applying various seepage flow conditions. Finally, a three-dimensional numerical model was established for the construction of cross passage during artificial freezing. To confirm the feasibility of the model, data from 53 points were continuously collected from the case study for more than 50 days. The proposed model delivers temperature results that are consistent with the field data.

Evolution Pattern of Tailings Flow from Dam Failure and the Buffering Effect of Debris Blocking Dams

Tailings ponds are the indispensable facilities in the mine production and operation. Once the dam is destabilized and damaged, it will pose a serious threat on the life and property of the downstream population and could also potentially cause an environmental disaster. With an engineering background, this paper dynamically and numerically simulates the evolution process of tailings flow from dam failure and the influence scope of any resulting disaster in context. The evolution characteristics of leaked tailings flow are analyzed at various downstream riverbed slopes and debris blocking dam settings. In addition, parameters such as flow rate, impact force and deposition range of leaked tailings flow at downstream arrival are studied, as well as their correlations. The results indicate that the flat terrains upstream and downstream of passage zone show a relatively larger area of inundation by tailings flow. Both the maximum and final downstream inundated ranges increase with the elevating slope of downstream riverbed, and the leaked tailings are deposited mainly in the nearby villages in front of the dam and the flat terrains of the downstream passage zone. Additionally, rational establishment of debris blocking dams on the downstream side is effective in diminishing the damage of tailings flow to the downstream section. This study can also provide an important basis for the quantitative evaluation of post-disaster influence scope for tailings pond as well as for the design of dam body.

The main trends in the dynamics of vegetation on the territory affected by the catastrophic eruption of Bezymyanny Volcano on March 30, 1956 (Kamchatka)

The transformation of the vegetation cover in the impact zone of the 1956 eruption, in territories covered by various deposits, is considered. As a result of a gigantic eruption (VEI 5), vegetation was exposed to a series of different volcanic impacts. Five main categories of events are distinguished: the movement of material of a huge volume of volcano edifice over a large distance as a result of a giant clastic avalanch, the pyroclastic surge of a direct blast, the pyroclastic flows, the formation of a giant eruptive cloud and ashfalls, as well as the lahars. The volume of erupted (initially high-temperature) deposits was, according to various estimates, in the amount of 1.35-1.5 km3, the volume of cold deposits of a clastic avalanche was 0.5-0.8 km3. The volume of lahar was 0.5 km3. The area covered by the pyroclastic wave of the directed explosion was about 500 km2. Within this lesion zone, deposits of pyroclastic flows have occupied 30-40 km2, and clastic avalanche deposits from 35 to 60 km2. Below 900 m above sea level (a.s.l.) these deposits buried cover of subalpine dwarf alder (dominant species is Alnus fruticosa) and mountain meadow vegetation, as well as forest vegetation (dominant species is Betula ermanii) at its upper limit. Forest and partially dwarf alder vegetation was destroyed on a vast territory mainly under the influence of a pyroclastic wave (in the altitude range from 700-800 to 200 m a.s.l.), as well as lahars (in the range of 250-50 m a.s.l.). Primary successions occur in the alpine and partially subalpine zone on avalanche deposits and pyroclastic flows deposits, as well as in the upper part of the zone impacted by pyroclastic surge of the direct blast (40-45 km2). In part of the territories where thick deposits of the lahars were formed, primary successions also probably occurred. In the zone of primary successions, deposits of a clastic avalanche are settled by plants most slowly due to not-favourable edaphic factors. The process is somewhat more efficient on the deposits of pyroclastic flows (the same ratio was noted on the Shiveluch Volcano). The surface overlapped by deposits of the pyroclastic surge is populated relatively quickly. Secondary succession occurs in the zone of damage to the forest and dwarf trees by the influence of a pyroclastic wave, as well as in the zone of passage of the lahars. Restoring of vegetation to its previous state will take from 50 to ~500 years on different deposits and in different parts of an impact zone.

POTENTIAL OF ULTRASOUND-GUIDED LUMBAR FACET RADIOFREQUENCY DENERVATION

The aim of the study was to evaluate the possibility of US navigation for Radiofrequency denervation (RFD) of the lumbar facets.Material and methods. The authors performed a prospective controlled cohort study which included 50 patients with chronic pain syndrome who underwent RFD LIII-SI facets on both sides. The main group (US) included 25 patients, who underwent US guided navigation with FScontrol of the correct placement of the cannula prior to ablation. In the control group (FS) the RFD was performed only under FS control. Patients were selected after preliminary test block of medial branch with 50% pain reduction from the baseline. Patients with overweight, spinal deformity, pronounced degenerative changes, spinal stenosis and developmental anomalies were not included in the study. For the evaluation of outcomes, the numeric pain scale NRS-11 and the Oswestry index (ODI) were used, the accuracy of the cannula position was assessed and factors determining the accuracy were searched.Results. As a result of the intervention, there was a significant decrease of NRS-11 and ODI criteria in both groups (p0.001), a positive outcome was achieved in 18 (72%) of US patients and 16 (64%) of FS patients, p = 0.564. Of the 200 attempts to position the cannula under the ultrasound control, 169 (84.5%) were successful, in most cases (187 out of 200, 93.5%) at least 3 attempts were required to reposition the cannula. The average time for performing the procedure under the ultrasound control was 47.3±1.13 minutes. The facet angle and procedure level were defined as predictors of the cannula positioning accuracy, odds ratio 0.93 (95% CI 0.894–0.963) and 0.51 (95% CI 0.32–0.805), respectively.Conclusion. RFD of lumbar facet under ultrasound navigation allows to achieve a relatively high accuracy of the cannula position into the zone of passage of the articular branch. The navigation capabilities are reduced at the level of LV and SI vertebrae due to structural features of the joints, namely coronary orientation of the facets with the formation of a narrow space between the transverse and upper articular process, which create difficulties for scanning. The disadvantage of ultrasound control is the lengthy procedure and the need for repeated reinsertion of the cannulae worsening the patient’s tolerance of procedure.

Lillooet Glacier basalts, southwestern British Columbia, Canada: products of Quaternary glaciovolcanism

The retreat of Lillooet Glacier (LG) has exposed a succession of pillow basalt and subordinate amounts of breccia and hyaloclastite. The lithofacies and physiographic setting suggest that the deposits have a glaciovolcanic origin and represent a partially dissected basaltic pillow-dominated tindar. Chemically, the LG volcanic rocks are basalt to basaltic andesite, and, as a group, they represent the highest-silica, Quaternary mafic products in the Garibaldi volcanic belt (GVB). Like other northern GVB (alkaline) basalts, they lack the Nb–Ta depletion signature typically associated with subduction-related products. Geochemical and petrologic analysis indicates that the LG basalts are comagmatic and that chemical variations within the suite are consistent with sorting of the observed phenocryst assemblage: olivine + plagioclase. Thermodynamic modeling establishes shallow, crustal, pre-eruptive storage conditions at &lt;2 kbar (1 kbar = 100 MPa; or 7.5 km) and an H2O content of 0.5–1 wt.%. We estimate that the LG basalts were erupted at the peak of, or during the waning stages of, Fraser glaciation (17–13 ka). The eruption produced an englacial lake that was &gt;150 m deep and that appears to have been sustained throughout the entire eruption (i.e., no discernible passage zone). Using hydrostatic constraints, we calculate a minimum overlying paleo-ice thickness of &gt;645 m and a paleo-ice surface elevation of &gt;1895 m above sea level.

Behavioral Patterns of Common Bottlenose Dolphins (Tursiops truncatus truncatus) Within the Galveston—Port Bolivar Ferry Lane

The objective of this study is to assess Tursiops truncatus truncatus (Common Bottlenose Dolphin) group behavior as a function of spatial, temporal, and vessel proximity variables within the Galveston—Port Bolivar ferry lane, in lower Galveston Bay, TX. This area is subjected to vessel traffic entering the Houston, Texas City, and Galveston ship channels and at risk for environmental accidents. We used the Galveston—Port Bolivar ferries as a platform of opportunity to observe group behavior within the ferry lane. We conducted 1412 hours of observation between 1 June and 30 November 2013 and then utilized canonical correspondence analysis to evaluate behavioral state as a function of spatial, temporal, and vessel-proximity variables. Principal response curve (PRC) analysis showed significant variation in behavioral states over time in the Bolivar and Galveston zones as compared to the passage zone. Chi-square goodness-of-fit tests showed significant deviations from expected behavior observation across zone and time block. These findings demonstrate finescale behavioral variability in an area of high anthropogenic activity.

Discontinuous Elastic Lamine in the Internal Iliac Artery in Lamb

Fragments from three hybrid Merino lambs were harvested from the internal iliac arteries and processed in order to conduct histological investigations. Structurally, these arteries fall under the muscle arteries category. AŽn one of the lambs we observed the absence of elastic laminae (internal and external) on a certain segment of the vessel cicumference. The absence of elastic laminae on a certain segment, only in one animal, does not seem to have a functional or pathological signification, thus we believe that we have intercepted the passage zone from transitional arteries to musclular ones.

Effects of deglaciation on the petrology and eruptive history of the Western Volcanic Zone, Iceland

New observations and geochemical analyses of volcanic features in the 170-km-long Western Volcanic Zone (WVZ) of Iceland constrain spatial and temporal variations in volcanic production and composition associated with the last major deglaciation. Subglacial eruptions represent a significant portion of the late Quaternary volcanic budget in Iceland. Individual features can have volumes up to ∼48 km3 and appear to be monogenetic. Subaqueous to subaerial transition zones provide minimum estimates of ice sheet thickness at the time of eruption, although water-magma interactions and fluctuating lake levels during eruption can lead to complex lithological sequences. New major and trace element data for 36 glacial and postglacial eruptive units, combined with observations of lava surface quality, passage zone heights, and 3He exposure ages of some glacial units, indicate a maximum in volcanic production in the WVZ during the last major ice retreat. Anomalously high volcanic production rates continue into the early postglacial period and coincide with significant incompatible element depletions and slightly higher CaO and SiO2 and lower FeO content at a given MgO. Subglacial units with strong incompatible element depletions also have lava surfaces that lack evidence of subsequent glaciation. These units likely formed after the onset of deglaciation, when rapidly melting ice sheets increased decompression rates in the underlying mantle, leading to anomalously high melting rates in the depleted upper mantle. This process also can explain the eruption of extremely depleted picritic lavas during the early postglacial period. These new observations indicate that the increased volcanic activity associated with glacial unloading peaked earlier than previously thought, before Iceland was completely ice free.

Polygonal feeder tubes filled with hydroclasts: a new volcanic lithofacies marking shoreline subaerial–submarine transition

This paper describes for the first time a new lithofacies that formed in the passage zone during the construction of pahoehoe lava-fed deltas in the north and NE coastal areas of Gran Canaria (Canary Islands, Atlantic Ocean). These lava-fed deltas, which are Pliocene in age, present similar lithofacies associations to those previously described in the literature, except for two distinct features: low abundance of hyaloclastites and a new lithofacies in the passage zone. This new lithofacies, which we propose to name ‘polygonal feeder tubes filled with hydroclasts’, comprises metre-scale lava feeder tubes with decimetre-scale coherent poorly vesicular and aphanitic rinds of polygonal morphology, filled with closely packed hydroclasts generated in situ . It represents the first stage in the interaction between seawater and thick lava flows entering the sea under the influence of a tidal regime, thus marking sea level. This lithofacies should be easily recognizable in ancient successions, and thus represents a useful marker of palaeoshorelines. Supplementary material: Sample preparation and sample geochemistry are available at http://www.geolsoc.org.uk/SUP18785 .

Nationalism's Exile: Godfrey Nangonya and SWAPO's Sacrifice in Southern Angola

Godfrey Nangonya hardly figures in any liberation narrative in southern Africa. Born and educated in the border region of Namibia/Angola, he gravitated to Cape Town and the ferment of radical, nationalist and pan-African politics in the late 1940s. Departing for Angola, he joined militants who founded the MPLA. He was imprisoned twice under the Portuguese and, because of the complications of plural political affiliations, twice after Angolan independence. This article explores Nangonya's transnational political, nationalist and carceral journeys, and especially the years 1974–75 when, as SWAPO's liaison officer with UNITA in southern Angola, he was ‘sacrificed’ by the Namibian liberation movement. It examines the open and volatile southern Angolan frontier region in a time of expanding historical possibilities for national liberation, a space that had to be forcibly stabilised, whether as a buffer zone for the South African military, a zone of passage for SWAPO guerrillas, or sovereign territory for the MPLA. The new Cold War dynamics soon resulted in a hardening of political boundaries and the narrowing of nationalist alignments and internal debates. Nangonya was exiled by a Namibian nationalism and its history that was purged of its plural alternative narratives, and which is only now slowly opening up to debate.

Miocene–Pliocene rocky shores on São Nicolau (Cape Verde Islands): Contrasting windward and leeward biofacies on a volcanically active oceanic island

North Atlantic islands in the Cape Verde Archipelago off the coast of West Africa commonly feature an elongated N–S shape in which reduced northern coasts and longer eastern shores absorb the brunt of wave activity and long-shore currents generated by prevailing North East Trade Winds. Located in the middle windward islands, São Nicolau is unusual in profile with an elongated E–W configuration that offers a broad target against high-energy, wind-driven waves. Conversely, the south shore of São Nicolau provides relatively wide shelter in a leeward setting. Reconstruction of the proto-island prior to the onset of the Main Eruptive stage during the Late Miocene at ~5.1Ma reveals a moderately smaller island with essentially the same E–W orientation. This study combines previous data with results from a detailed stratigraphic log based on Upper Miocene limestone deposits on the island's south flank for comparison with stratigraphic profiles of Upper Miocene limestone from the island's northeast quarter. Logs from a Pliocene sandy limestone outcropping on the south-central coast of São Nicolau give added context to the diversity of marine invertebrates, including branching coral colonies and delicate ramose bryozoans that found shelter in a leeward setting. Whole rhodoliths contribute the main fabric of carbonates deposited against rocky shores on the northern, exposed side of the Miocene island, whereas only traces of worn rhodoliths and rhodolith sand occur as in finer Miocene grainstone on the island's southern, protected side. Miocene and Pliocene carbonate deposits were terminated by submarine flows on an actively growing volcanic island. The passage zone from submarine to subaerial flows on the island's flanks makes a useful meter-stick to gauge absolute water depth at the moment of local extinction by volcanic activity.

Pyroclastic passage zones in glaciovolcanic sequences

Volcanoes are increasingly recognized as agents and recorders of global climate variability, although deciphering the linkages between planetary climate and volcanism is still in its infancy. The growth and emergence of subaqueous volcanoes produce passage zones, which are stratigraphic surfaces marking major transitions in depositional environments. In glaciovolcanic settings, they record the elevations of syn-eruptive englacial lakes. Thus, they allow for forensic recovery of minimum ice thicknesses. Here we present the first description of a passage zone preserved entirely within pyroclastic deposits, marking the growth of a tephra cone above the englacial lake level. Our discovery requires extension of the passage-zone concept to accommodate explosive volcanism and guides future studies of hundreds of glaciovolcanic edifices on Earth and Mars. Our recognition of pyroclastic passage zones increases the potential for recovering transient paleolake levels, improving estimates of paleo-ice thicknesses and providing new constraints on paleoclimate models that consider the extents and timing of planetary glaciations.