Natural coastal mechanisms — flume and field experiments on links between biology,sediments, and flow     

Patrick L. Friend  Carl L. Amos 《Continental Shelf Research》2007

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Estuarine mud flocculation properties determined using an annular mini-flume and the LabSFLOC system     

A.J. Manning  P.L. Friend  N. Prowse  C.L. Amos 《Continental Shelf Research》2007

Most entrained estuarine sediment mass occurs as flocs. Parameterising flocculation has proven difficult as it is a dynamically active process dependent on a set of complex interactions between the sediment, fluid and the flow. However the natural variability in an estuary makes it difficult to study the factors that influence the behaviour of flocculation in a systematic manner. This paper presents preliminary results from a laboratory study that examined how floc properties of a natural estuarine mud from the Medway (UK), evolved in response to varying levels of suspended sediment concentration and induced turbulent shearing. The experiments utilised the LabSFLOC floc video camera system, in combination with an annular mini-flume to shear the suspended sediment slurries. The flows created in the mini-flume produced average shear stresses, at the floc sampling height, ranging from 0.01 N m⁻² to a peak of 1.03 N m⁻². Nominal suspended particulate matter concentrations of 100, 600 and 2000 mg l⁻¹ were introduced into the flume. The experimental runs produced individual flocs ranging in size from microflocs of 22.2 μm to macroflocs 583.7 μm in diameter. Average settling velocities ranged from 0.01 to 26.1 mm s⁻¹, whilst floc effective densities varied from 3.5 up to 2000 kg m⁻³. Low concentration and low shear stress were seen to produce an even distribution of floc mass between the macrofloc (>160 μm) and microfloc (<160 μm) fractions. As both concentration and stress rose, the proportion of macrofloc mass increased, until they represented over 80% of the suspended matter. A maximum average macrofloc settling velocity of 3.3 mm s⁻¹ was attained at a shear stress of 0.45 N m⁻². Peak turbulence conditions resulted in deflocculation, limiting the macrofloc fall velocity to only 1.1 mm s⁻¹ and placing over 60% of the mass in the microfloc size range. A statistical analysis of the data suggests that the combined influence of both suspended concentration and turbulent shear controls the settling velocity of the fragile, low density macroflocs.  相似文献   

The March 25 and 29, 2016 landslide-induced debris flow at Clapar,Banjarnegara, Central Java     

Guruh Samodra  Danang Sri Hadmoko  Ghalih Nur Wicaksono  Indriya Parahita Adi  Maulana Yudinugroho  Sandy Budi Wibowo  Hatma Suryatmojo  Taufik Hery Purwanto  Barandi Sapta Widartono  Franck Lavigne 《Landslides》2018,15(5):985-993

The Clapar landslide induced debris flow consisted of the Clapar landslide occurred on 24 March 2017 and the Clapar debris flow occurred on 29 March 2017. The first investigation of the Clapar landslide induced debris flow was carried out two months after the disaster. It was followed by UAV mapping, extensive interviews, newspaper compilation, visual observation and field measurements, and video analysis in order to understand chronology and triggering mechanism of the landslide induced debris flow in Clapar. The 24 March 2016 landslide occurred after 5 hours of consecutive rainfall (11,2 mm) and was affected by combination of fishponds leak and infiltration of antecedent rain. After five days of the Clapar landslide, landslide partially mobilized to form debris flow where the head scarp of debris flow was located at the foot of the 24 March 2016 landslide. The Clapar debris flow occurred when there was no rainfall. It was not generated by rainstorm or the surface erosion of the river bed, but rather by water infiltration through the crack formed on the toe of the 24 March 2016 landslide. Supply of water to the marine clay deposit might have increased pore water pressure and mobilized the soil layer above. The amount of water accumulated in the temporary pond at the main body of the 24 March 2016 landslide might have also triggered the Clapar debris flow. The area of Clapar landslide still shows the possibility of further retrogression of the landslide body which may induce another debris flow. Understanding precursory factors triggering landslides and debris flows in Banjarnegara based on data from monitoring systems and laboratory experiments is essential to minimize the risk of future landslide.  相似文献   

The effect of changes in tidal range on a sublittoral macrotidal sequence,bay of fundy,Canada     

C. L. Amos  B. A. Zaitlin 《Geo-Marine Letters》1984,4(3-4):161-169

Independent evidence of changes in sea level and tidal range in the Bay of Fundy during the last 9000 years is used to evaluate the lithologies in 17 cores from the sublittoral part of Chignecto Bay. The composite tidal sequence identified is complex because of changes from microtidal through mesotidal to macrotidal conditions associated with changing water depths. Despite the complex stratigraphy, lithology correlates well with the depositional environment on a bed-by-bed basis. We postulate that such variations in tidal range are important to the interpretation of tidalite deposits from the geologic record.  相似文献   

Gem corundum deposits of Madagascar: A review     

Amos Fety Michel Rakotondrazafy  Gaston Giuliani  Daniel Ohnenstetter  Anthony E. Fallick  Saholy Rakotosamizanany  Alfred Andriamamonjy  Thogne Ralantoarison  Madison Razanatseheno  Yohann Offant  Virginie Garnier  Henri Maluski  Christian Dunaigre  Dietmar Schwarz  Voahangy Ratrimo 《Ore Geology Reviews》2008,34(1-2):134

Madagascar is one of the most important gem-producing countries in the world, including ruby and sapphires. Gem corundum deposits formed at different stages in the geological evolution of the island and in contrasting environments. Four main settings are identified: (1) Gem corundum formed in the Precambrian basement within the Neoproterozoic terranes of southern Madagascar, and in the volcano-sedimentary series of Beforona, north of Antananarivo. In the south, high-temperature (700 to 800 °C) and low-pressure (4 to 5 kbar) granulites contain deposits formed during the Pan-African orogenesis between 565 and 490 Ma. They accompany mafic and ultramafic complexes (ruby deposits of the Vohibory group), skarns at the contact between Anosyan granites and the Proterozoic Tranomaro group (sapphire deposits of the Tranomaro–Andranondambo district), and shear-zone corridors cross-cutting feldspathic gneisses, cordieritites and clinopyroxenites in the Tranomaro, Vohimena and Androyan metamorphic series (biotite schist deposits of Sahambano and Zazafotsy, cordieritites of Iankaroka and Ambatomena). The circulation of fluids, especially along discontinuities, allowed in-situ alkaline metasomatism, forming corundum host rocks related to desilicified granites, biotitites, “sakenites” and “corundumites”. (2) Gem corundum also occurs in the Triassic detrital formations of the Isalo group, as giant palaeoplacers in the Ilakaka–Sakaraha area. Here, sapphires and rubies may come from the metamorphic granulitic terranes of southern Madagascar. (3) Gem corundum deposits occur within the Neogene-Quaternary alkali basalts from Ankaratra (Antsirabe–Antanifotsy area) and in the Ambohitra Province (Nosy Be, Ambato and Ambondromifehy districts). Primary deposits are rare, except at Soamiakatra where ruby in gabbroic and clinopyroxenite xenoliths within alkali-basalts probably derive from mantle garnet peridotites. The blue-green-yellow sapphires typical of basaltic fields are always recovered in palaeoplacer (in karst formed upon Jurassic limestones from the Montagne d'Ambre, Antsiranana Province) and alluvial and soil placers (Ankaratra volcanic massif). (4) Deposits occur within Quaternary eluvial, colluvial and alluvial concentrations, such as high-quality rubies from the Andilamena and Vatomandry deposits.  相似文献   

Janus-Faced Linkages: Understanding External Actors in Community-Based Natural Resource Management in Southern Thailand     

Nur Shafwaty Sa’at 《社会与自然资源》2018,31(7):773-789

In community-based natural resource management, there is an emerging body of research on the work of external actors and their influence in community–resource interrelationships and community management decisions. Contributing to this research, this study examined the work of external actors using findings from semistructured interviews and participant observations conducted in Klong Prasong subdistrict, Krabi Province, Thailand, in mid-2014. The external actors, through Janus-faced linkages, are able to influence community–resource interrelationships and management approaches both positively and negatively. This case study also revealed university researchers, ecotourists, and private investors as non-conventional external actors. By influencing decision-making structures and environmental stewardship, external actors impact on the governance of a community natural resource.  相似文献   

First insights into the demography of the rare gorgonian Spinimuricea klavereni in the Mediterranean Sea          下载免费PDF全文

Nur Eda Topçu  Bayram Öztürk 《Marine Ecology》2016,37(5):1154-1160

We present the results of the first study to highlight the demography, morphometry and growth rates of Spinimuricea klavereni, a rare Mediterranean endemic gorgonian exceptionally common in shallow depths of the Northeast Marmara Sea. In the study area, this species forms vast populations on rocks, boulders and attached to pebbles/stones/shells on soft substrates between 20 and 45 m depth, with a total average density of 0.3 colonies·m^?2 but comprising patches up to 3 colonies·m^?2. Colonies, which are on average 42.9 (±20.1) cm in height, can reach up to 110 cm. Unlike other Mediterranean gorgonians, the colonies studied here showed fast growth rates that decreased with increasing colony height, between 1.5–11.1 and 4.96 ± 3.01 cm·year^?1 on average. The low necrosis and high growth rates displayed by this species in the Northeast Marmara Sea confirm the previously hypothesized opportunistic behaviour of the species. The unique community consisting of S. klavereni and other rare gorgonian/soft corals has limited distribution in this area and should be considered to be a vulnerable marine ecosystem. Therefore we recommend that some conservation measures are taken, including the prohibition of all fisheries and anchoring over these assemblages.  相似文献   

Sedimentological interpretation of an Ediacaran delta: Bonney Sandstone,South Australia     

J. W. Counts  F. Rarity  R. B. Ainsworth  K. J. Amos  T. Lane  S. Morón 《Australian Journal of Earth Sciences》2016,63(3):257-273

The type section of the late Ediacaran (ca 565 Ma) Bonney Sandstone in South Australia provides an opportunity to interpret a succession of Precambrian clastic sediments using physical sedimentary structures, lithologies and stacking patterns. Facies models, sequence stratigraphic analysis, and process-based architectural classification of depositional elements were used to interpret depositional environments for a series of disconformity-bounded intervals. This study is the first detailed published work on the Bonney Sandstone, and provides additional context for other Wilpena Group sediments, including the overlying Rawnsley Quartzite and its early metazoan fossils. Results show that the ～300 m-thick section studied here shows a progressive change from shallow marine to fluvially dominated sediments, having been deposited in storm-dominated shelf and lower shoreface environments, lower in the section, and consisting primarily of stacked channel sands, in a proximal deltaic environment near the top. Based on the degree of influence of wave, tidal or fluvial depositional processes, shallow marine sediments can be classified into beach, mouth bar, delta lobe and channel depositional elements, which can be used to assist in predicting sandbody geometries when only limited information is available. Sediments are contained within a hierarchical series of regressive, coarsening-upward sequences, which are in turn part of a larger basin-scale sequence that likely reflects normal regression and filling of accommodation throughout a highstand systems tract. Paleogeographic reconstructions suggest the area was part of a fluvially dominated clastic shoreline; this is consistent with previous reconstructions that indicate the area was on the western edge of the basin adjacent to the landward Gawler Craton. This research fills in a knowledge gap in the depositional history of a prominent unit in the Adelaide Rift Complex and is a case study in the interpretation of ancient deposits that are limited in extent or lacking diagnostic features.  相似文献   

Rotation, planets, and the 'second parameter' of the horizontal branch     

Noam Soker  Amos Harpaz 《Monthly notices of the Royal Astronomical Society》2000,317(4):861-866

We analyse the angular momentum evolution from the red giant branch (RGB) to the horizontal branch (HB) and along the HB. Using rotation velocities for stars in the globular cluster M13, we find that the required angular momentum for the fast rotators is up to 1–3 orders of magnitude (depending on some assumptions) larger than that of the Sun. Planets of masses up to 5 times Jupiter's mass and up to an initial orbital separation of ~2 au are sufficient to spin-up the RGB progenitors of most of these fast rotators. Other stars have been spun-up by brown dwarfs or low-mass main-sequence stars. Our results show that the fast rotating HB stars have been probably spun-up by planets, brown dwarfs or low-mass main-sequence stars while they evolved on the RGB. We argue that the angular momentum considerations presented in this paper further support the 'planet second parameter' model. In this model, the 'second parameter' process, which determines the distribution of stars on the HB, is interaction with low-mass companions, in most cases with gas-giant planets, and in a minority of cases with brown dwarfs or low-mass main-sequence stars. The masses and initial orbital separations of the planets (or brown dwarfs or low-mass main-sequence stars) form a rich spectrum of different physical parameters, which manifests itself in the rich varieties of HB morphologies observed in the different globular clusters.  相似文献   

A catchment‐scale assessment of anabranching in the 143 000 km2 Fitzroy River catchment,north‐eastern Australia     

Kathryn J. Amos  Jacky C. Croke  Andrew O. Hughes  Joanne Chapman  Ingrid Takken  Leo Lymburner 《地球表面变化过程与地形》2008,33(8):1222-1241

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