Computer-simulation models of scoria cone degradation   总被引：2，自引：0，他引：2  

Donald M. Hooper  Michael F. Sheridan 《Journal of Volcanology and Geothermal Research》1998,83(3-4)

Long-term erosional modifications of the relatively simple morphology of scoria (‘cinder') cones are ideally suited for study by field and computer-simulation methods. A series of temporally-distinct cones in the San Francisco and Springerville volcanic fields of Arizona provides the foundation for documenting the degradational evolution of scoria cones in a semi-arid climate. Progressive changes due to erosion are illustrated by the systematic decrease with increasing age of various morphometric parameters, including scoria cone height, cone height/width ratio (H_co/W_co), crater depth/width ratio, and slope angle. For example, Holocene–latest Pleistocene cones in the San Francisco field have a mean H_co/W_co value of 0.178±0.041, a mean maximum slope angle of 29.7±4.2°, and a mean average slope angle of 26.4±7.3°, whereas the group of Pliocene cones have values of 0.077±0.024, 20.5±5.8°, and 8.7±2.7°, respectively. Comparative morphology of scoria cones is a potentially useful dating tool for mapping volcanic fields.In order to better understand the degradational modifications of these volcanic landforms, we have developed a numerical approach to simulate the surficial processes responsible for the erosion of a typical scoria cone. The simulation algorithm can apply either a linear diffusion-equation model or a model with a nonlinear transport law. Using a finite-difference formulation, the simulation operates upon a three-dimensional scoria cone input as a matrix of elevation values. Utilizing both field and model results, the correlation between changing H_co/W_co value, cone age, and computer time step was expressed graphically to derive comprehensive values of the transport or diffusion coefficient (D_f) for both volcanic fields. For the San Francisco volcanic field, D_f had a calculated value of 21.4 m²/kyr for the linear model and 5.3 m/kyr for the nonlinear model, while for the Springerville volcanic field D_f had a calculated value of 24.4 m²/kyr for the linear model and 6.3 m/kyr for the nonlinear model.  相似文献   

The radiocarbon budget for Mono Lake: an unsolved mystery     

Wallace S. Broecker  Rik Wanninkhof  Guy Mathieu  Tsung-Hung Peng  Scott Stine  Steve Robinson  Andy Herczeg  Minze Stuiver 《Earth and Planetary Science Letters》1988,88(1-2)

Since 1957 the ¹⁴C/C ratio of the dissolved inorganic carbon in Mono Lake has risen by about 60‰. The magnitude of this increase is about four times larger than that expected from the invasion of bomb-produced¹⁴C from the atmosphere. We have eliminated the following explanations: (1) measurement error, (2) an unusually high physical exchange rate for non-reactive gases, (3) inorganic enhancement of the CO₂ exchange rate, and (4) biological enhancement of the CO₂ exchange rate. Clandestine disposal of waste radiocarbon remains a dark-horse explanation.In the course of our investigations we have uncovered evidence for at least one episodic input of radiocarbon-free carbon to the lake over the last 1000 years. We speculate that this injection was related to a hydrothermal event resulting from sublacustrine volcanic activity.  相似文献   

The Geochemical Evolution of Riparian Ground Water in a Forested Piedmont Catchment   总被引：2，自引：0，他引：2  

Douglas A. Burns  L. Niel Plummer  Jeffrey J. McDonnell    Eurybiades Busenberg  Gerolamo C. Casile  Carol Kendall  Richard P. Hooper  James E. Freer  Norman E. Peters  Keith Beven  Peter Schlosser 《Ground water》2003,41(7):913-925

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Comment on “a test of annual resolution in stalagmites using tree rings”     

Andy Baker  Dominique Genty 《Quaternary Research》2003,59(3):476-478

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森林生态服务市场的开发     

Ian Powell  Andy White  Natasha Landell-Mills  刘硕  王学全 《湿地科学与管理》2002,(4):39-43

<正> 森林提供许多有价值的生态服务,诸如保护流域和生物多样性以及贮存碳素等,现已引起企业、政府乃至个人越来越多的关注,同时人们也意识到随着森林这些功能的退化甚至丧失所带来的危险和代价。这种退化既能引起洪水、山崩之类的局部灾难,也会导致全球气候变化之类的广泛影响。  相似文献   

A Cromerian Complex stalagmite from the Mendip Hills,England     

Andy Baker  Christopher J. Caseldine  Jackie Hatton  Christopher J. Hawkesworth  Alfred G. Latham 《第四纪科学杂志》1997,12(6):533-537

In order to provide a better chronological constraint on a British Middle Pleistocene interglacial, a large stalagmite boss from the Mendip Hills was selected for palaeoclimate data using pollen analysis. Dating analyses by thermal ionisation mass spectrometry (TIMS) of uranium–thorium ratios and by magnetostratigraphy constrain the age of the sample to 450–780 ka. The isotopic consistency of the TIMS analyses, plus the presence of luminescence laminations, suggest that the sample has been preserved under closed-system conditions. Pollen assemblages have been recovered from the speleothems, despite the fact that the pH of calcite deposition is usually greater than 7. Furthermore the evidence presented here indicates that the pollen was probably transported by the speleothem feedwater, rather than entering the cave aerially. The pollen record contained within the stalagmite is interpreted as early–mid-interglacial but does not have clear Cromerian affinity. © 1997 John Wiley & Sons, Ltd.  相似文献   

Organic carbon fluxes of a glacier surface: A case study of Foxfonna,a small Arctic glacier     

Krystyna A. Koziol  Helen L. Moggridge  Joseph M. Cook  Andy J. Hodson 《地球表面变化过程与地形》2019,44(2):405-416

Arctic glaciers are rapidly responding to global warming by releasing organic carbon (OC) to downstream ecosystems. The glacier surface is arguably the most biologically active and biodiverse glacial habitat and therefore the site of important OC transformation and storage, although rates and magnitudes are poorly constrained. In this paper, we present measurements of OC fluxes associated with atmospheric deposition, ice melt, biological growth, fluvial transport and storage (in superimposed ice and cryoconite debris) for a supraglacial catchment on Foxfonna glacier, Svalbard (Norway), across two consecutive years. We found that in general atmospheric OC input (averaging 0.63 ± 0.25 Mg a^-1 total organic carbon, i.e. TOC, and 0.40 ± 0.22 Mg a^-1 dissolved organic carbon, i.e. DOC) exceeded fluvial OC export (0.46 ± 0.04 Mg a^-1 TOC and 0.36 ± 0.03 Mg a^-1 DOC). Early in the summer, OC was mobilised in snowmelt but its release was delayed by temporary storage in superimposed ice on the glacier surface. This delayed the export of 28.5% of the TOC in runoff. Biological production in cryoconite deposits was a negligible potential source of OC to runoff, while englacial ice melt was far more important on account of the glacier's negative ice mass balance (–0.89 and –0.42 m a^-1 in 2011 and 2012, respectively). However, construction of a detailed OC budget using these fluxes shows an excess of inputs over outputs, resulting in a net retention of OC on the glacier surface at a rate that would require c. 3 years to account for the OC stored as cryoconite debris. © 2018 John Wiley & Sons, Ltd.  相似文献   

新型双船起重拆除平台试验研究   总被引：1，自引：1，他引：0  

李巍  胡智焕  李欣  孙浩  WANG Andy  田新亮  张卫东 《海洋工程》2020,38(1):30-41

拆除大型海上结构物是一项非常复杂且充满挑战的工程。现提出一种新型海上平台拆除方案,该方案利用三条半潜船来代替具有重型起重装置的单一船舶,通过两艘相同的半潜船将平台上层建筑托起,随后运至第三艘半潜船上完成平台拆除。在风浪流作用下,半潜船和平台的所处方位和运动姿态一直处于动态变化中,这对船舶调节压载的稳定性以及双船运动的同步性提出了要求。为了确保该方案的高效性和安全性,设计了一套完整的模型试验装置,包括船舶模型、平台拆卸辅助设备、六自由度运动采集与分析系统、控制系统、无线通讯系统以及测量系统。开展了相应的水池试验,试验结果验证了双船起重拆除平台方案中双船协同运输这一关键环节的可行性和安全性。  相似文献   

Influence of vegetation cover on sand transport by wind: field studies at Owens Lake,California     

Nicholas Lancaster  Andy Baas 《地球表面变化过程与地形》1998,23(1):69-82

Field studies conducted at Owens Lake, California, provide direct measurements of sand flux on sand sheets with zero to 20 per cent cover of salt grass. Results from 12 different sand transport events show that aerodynamic roughness length and threshold wind shear velocity increase with vegetation cover as measured by vertically projected cover and roughness density (λ). This results in a negative exponential decrease in sediment flux with increasing vegetation cover such that sand transport is effectively eliminated when the vertically projected cover of salt grass is greater than 15 per cent. A general empirical model for the relation between sand flux and vegetation cover has been derived and can be used to predict the amount of vegetation required to stabilize sand dune areas. © 1998 John Wiley & Sons, Ltd.  相似文献   

Soil water movement and nutrient cycling in semi-arid rangeland: vegetation change and system resilience     

Andy J. Dougill  A. Louise Heathwaite  David S. G. Thomas 《水文研究》1998,12(3):443-459

Recent decades have seen rapid intensification of cattle production in semi-arid savannah ecosystems, increasingly on formalized ranch blocks. As a result, vegetation community changes have occurred, notably bush encroachment (increased bush dominance) in intensively grazed areas. The exact causes of this vegetation change remain widely debated. Previous studies have suggested: (i) increased leaching of water and nutrients into the subsoil in intensively grazed areas provides deeper rooting bush species with a competitive advantage for soil water and nutrients, and (ii) nutrient leaching may be exacerbated by nutrient inputs from cattle dung and urine. Our research in the Eastern Kalahari showed that in infertile sandy soils both the magnitude of soil water and concentration of soil nutrients leached into the subsoil is largely unaffected by the ecological and biochemical effects of increased cattle use. We found that despite the high soil hydraulic conductivity ( &greaterno;12 cm h⁻¹), relatively high subsoil moisture contents and the restriction of water movement to matrix flow pathways prevent leaching losses beyond the rooting zone of savannah grass species. No significant differences in patterns of soil water redistribution were noted between bush dominant and grass dominant sites. We also found that the low nutrient status of Kalahari soils and leachate movement as matrix flow combine to allow nutrient adsorption on to soil particles. Nutrient adsorption ensures that nitrogen and phosphorus cycling remains topsoil dominated even following the removal of vegetation and direct nutrient inputs in cattle dung and urine. This conclusion refutes environmental change models that portray increases in the leaching of soil water and available nitrogen as a major factor causing bush encroachment. This provides a possible explanation for the now widely cited, but hitherto unexplained, resilience of dryland soils. We suggest that infertile sandy soils appear resilient to changes in soil water distribution and nutrient availability caused by increased cattle use. Hence, soil characteristics contribute to the resilience to permanent ecological change that is increasingly recognized as an attribute of semi-arid rangelands. © 1998 John Wiley & Sons, Ltd.  相似文献