Hydromechanical Rock Mass Fatigue in Deep-Seated Landslides Accompanying Seasonal Variations in Pore Pressures     

Giona Preisig  Erik Eberhardt  Megan Smithyman  Alexander Preh  Luca Bonzanigo 《Rock Mechanics and Rock Engineering》2016,49(6):2333-2351

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Chemical and physical weathering in a hot‐arid,tectonically active alluvial system of Anza Borrego Desert,California          下载免费PDF全文

Young Ji Joo  Megan E. Elwood Madden  Gerilyn S. Soreghan 《Sedimentology》2016,63(5):1065-1083

Investigation of chemical and physical weathering of bedrock and alluvial sediment in the Anza Borrego Desert, California, sheds light on weathering processes in hot‐arid systems and clarifies interpretations of climate from alluvial sediment. All of the alluvial sediment in the study area emanates from Cretaceous tonalite of the Peninsular Range, enabling exploration of the effects of external variables – climate, transport distance and tectonics – on the physical and chemical properties of the sediment. Chemical weathering in this area is dominated by plagioclase alteration observed in both bedrock outcrops and sediment, evinced most clearly by changes in the Eu anomaly. Biotite chemical weathering, manifested by interlayer K⁺ loss, is not evident in bedrock, but clearly observed in the sediment. Despite the weak intensity of chemical weathering (Chemical Index of Alteration = 56 to 62), fine‐grained (<63 μm) sediment displays a clear weathering trend in A–CN–K space and contains up to 25% clay minerals. Physical abrasion and grain‐size reduction in biotite during transport predominates in the sediment, whereas physical (insolation) weathering affecting bedrock is inferred from estimates of differential thermal expansion of mineral phases in response to extreme temperature changes in the study area. Chemical alteration and Brunauer–Emmett–Teller surface area both increase within the active Elsinore fault zone at the distal end of the depositional transect, reflecting tectonic‐induced fracturing and associated accelerated weathering. Extensive fracturing, together with a more humid Pleistocene climate, probably facilitated in situ bedrock weathering, preceding arid alluvial deposition in the Holocene. This study demonstrates that both climate and tectonic processes can affect chemical and physical weathering, resulting in alteration of plagioclase, leaching of K⁺ from biotite in the sediment and formation of clay minerals, even in hot, arid systems.  相似文献   

The race is not to the swift     

Megan K Pickett  rew J Lim 《Astronomy& Geophysics》2004,45(1):1.12-1.17

Megan K Pickett and Andrew J Lim examine the role of spirals in protoplanetary disks and the formation of gas giant planets, and find that slower may be better than faster, if planets are to endure.  相似文献   

Estimating restorable wetland water storage at landscape scales   总被引：1，自引：0，他引：1       下载免费PDF全文

Charles Nathan Jones  Grey R. Evenson  Daniel L. McLaughlin  Melanie K. Vanderhoof  Megan W. Lang  Greg W. McCarty  Heather E. Golden  Charles R. Lane  Laurie C. Alexander 《水文研究》2018,32(2):305-313

Globally, hydrologic modifications such as ditching and subsurface drainage have significantly reduced wetland water storage capacity (i.e., volume of surface water a wetland can retain) and consequent wetland functions. While wetland area has been well documented across many landscapes and used to guide restoration efforts, few studies have directly quantified the associated wetland storage capacity. Here, we present a novel raster‐based approach to quantify both contemporary and potential (i.e., restorable) storage capacities of individual depressional basins across landscapes. We demonstrate the utility of this method by applying it to the Delmarva Peninsula, a region punctuated by both depressional wetlands and drainage ditches. Across the entire peninsula, we estimated that restoration (i.e., plugging ditches) could increase storage capacity by 80%. Focusing on an individual watershed, we found that over 59% of restorable storage capacity occurs within 20 m of the drainage network, and that 93% occurs within 1 m elevation of the drainage network. Our demonstration highlights widespread ditching in this landscape, spatial patterns of both contemporary and potential storage capacities, and clear opportunities for hydrologic restoration. In Delmarva and more broadly, our novel approach can inform targeted landscape‐scale conservation and restoration efforts to optimize hydrologically mediated wetland functions.  相似文献   

The transition from symmetric to baroclinic instability in the Eady model   总被引：1，自引：1，他引：0  

Megan A. Stamper  John R. Taylor 《Ocean Dynamics》2017,67(1):65-80

Here, we explore the transition from symmetric instability to ageostrophic baroclinic instability in the Eady model; an idealised representation of a submesoscale mixed layer front. We revisit the linear stability problem considered by Stone (J Atmos Sci, 23, 390–400, (Stone 1966)), Stone (J Atmos Sci, 27, 721–726, (Stone 1970)), Stone (J Atmos Sci, 29, 419–426, (Stone 1972)) with a particular focus on three-dimensional ‘mixed modes’ (which are neither purely symmetric or baroclinic) and find that these modes can have growth rates within just a few percent of the corresponding two-dimensional growth rate maximum. In addition, we perform very high resolution numerical simulations allowing an exploration of the transition from symmetric to baroclinic instability. Three-dimensional mixed modes represent the largest contribution to the turbulent kinetic energy during the transition period between symmetric and baroclinic instability. In each simulation, we see the development of sharp fronts with associated high rms vertical velocities of up to 30 mm s^?1. Furthermore, we see significant transfer of energy to small scales, demonstrated by time-integrated mixing and energy dissipation by small-scale three-dimensional turbulence totalling about 30 % of the initial kinetic energy in all cases.  相似文献   

The migrant anchovy fishery in Kabui Bay,Raja Ampat,Indonesia: Catch,profitability, and income distribution     

Megan Bailey  Christovel Rotinsulu  U. Rashid Sumaila 《Marine Policy》2008

We estimate the unregulated catch and fisher income of the Kabui Bay migrant anchovy fishery operating in the Raja Ampat regency, Papua, Indonesia. Interviews with migrant fishers were conducted in April and November 2006, and estimates were generated through Monte Carlo simulations. Anchovy fisher income averaged US $1835 per year, about twice the average fisher income in the area. The income levels estimated by this study suggests that there is potential for the Raja Ampat Fisheries Bureau to capture some economic rent from the fishery to help fund a fisheries management program, from which Raja Ampat could benefit.  相似文献   

Characterizing sources of groundwater to a tropical coastal lagoon in a karstic area using radium isotopes and water chemistry   总被引：2，自引：1，他引：1  

Megan B. Young  Meagan Eagle Gonneea  Derek A. Fong  Willard S. Moore  Jorge Herrera-Silveira  Adina Paytan   《Marine Chemistry》2008,109(3-4):377

Radium isotopes (²²³Ra, ²²⁴Ra, ²²⁶Ra, and ²²⁸Ra) and water chemistry were used to identify two chemically distinct sources of submarine groundwater discharge (SGD) in Celestún Lagoon, Yucatán, Mexico. Low salinity groundwater discharging from springs within the lagoon has previously been identified and extensively sampled for nutrient concentrations. However, a second type of groundwater discharging into the lagoon was detected during this study using radium isotope activity measurements. This second type of groundwater is characterized by moderate salinities (within the range of lagoon salinities) and very elevated radium activities in comparison to the low salinity groundwater, mixed lagoon water, and seawater. Further analysis showed that the two types of groundwater also have distinct chloride, strontium, and sulfate ratios, along with slightly different nutrient concentrations. Groundwater discharge occurs through large and small springs scattered throughout the lagoon, and both types of groundwater were detected discharging from one of the larger springs. The relative proportions of low salinity groundwater and brackish high radium groundwater varied over the tidal cycle. In order to better understand the relative contributions of each type of groundwater to the lagoon, a three end-member mixing model based on the distinct chemical and isotopic compositions of both types of groundwater and of seawater was used to estimate the distribution of each water type throughout the lagoon in different seasons. This study suggests that substantial groundwater discharge to the lagoon can occur during both dry and rainy seasons. The presence of two groundwater sources has implications for monitoring and protection of the Celestún Lagoon Biosphere Reserve, since the two sources may have different susceptibilities to anthropogenic contamination depending on their respective recharge area and recharge rates.  相似文献   

Aligning tourist,industry and government expectations: A case study from the swim with whales industry in Tonga     

Megan Kessler  Robert Harcourt 《Marine Policy》2010

Swimming with humpback whales in the Kingdom of Tonga is a growing industry that provides important revenue for a small Pacific Island economy. However the sustainability of this industry has been questioned due to its potential impact on the animals involved. The activity focuses on an ‘endangered’ subpopulation of humpback whales, with swimming occurring in the breeding area primarily with groups of animals containing young calves. This paper examines the relationship between the existing Tongan Government draft regulations and Tonga Whale Watching Operator Association guidelines that control the industry and visitor expectations about the management of the activity. There is significant support from visitors for strong, easy to understand and enforceable regulations governing the swim with whales industry. There is a clear correlation between current moves to strengthen Government regulations and the expectation from visitors that their activity is, and will be, conducted in a sustainable manner. The study recommends that to ensure compliance with regulations, appropriate management fees should be charged, visitors should be engaged in environmental education activities and further research should be conducted on the impacts of swimming with humpback whales.  相似文献   

Reuse of Drinking Water Treatment Waste for Remediation of Heavy Metal Contaminated Groundwater     

Ryan R. Holmes  Megan L. Hart  John T. Kevern 《Ground Water Monitoring & Remediation》2019,39(4):69-79

Lime softening produces an estimated 10,000 metric tons of dry drinking water treatment wastes (DWTW) per year, costing an estimated one billion dollars annually for disposal worldwide. Lime softening wastes have been investigated for reuse as internal curing agents or supplementary cementitious materials in concrete as well as a high-capacity sorbent for heavy metal removal. Lead, cadmium, and zinc are common heavy metals in groundwater contaminated by mine tailings. Cement-based filter media (CBFM) are a novel material-class for heavy metal remediation in groundwater. This study investigated the incorporation of DWTW as a recycled, low-cost additive to CBFM for the removal of lead, cadmium, and zinc. Jar testing at three different metal concentrations and breakthrough column testing using synthetic groundwater were performed to measure removal capacity and reaction kinetics. Jar testing results show as DWTW content increases at low concentrations, removal approaches 100% but at high metal concentrations removal decreases due to saturation or exhaustion of the removal mechanisms. Removal occurs through the formation of metal carbonate precipitates, surface sorption, and ion exchange with calcium according to the preferential series Pb⁺² > Zn⁺² > Cd²⁺. Removal kinetics were also measured through column testing and exceeded estimated calculations derived from batch jar testing isotherms due to the large formation of oolitic metal carbonates. Lead, cadmium, and zinc was concentrated in the column precipitates from 0.29, 0.23, and 20.0 μg/g in the influent solution to approximately 200, 130, 14,000 μg/g in the reacted DWTW-CBFM. The control and DWTW-CBFM columns had statically similar removal for zinc and lead. In the DWTW-CBFM, cadmium had decreased removal of approximately 25% due to proportionately decreased hydroxide content from cement replacement with 25% DWTW. This study shows the potential for DWTW as an enhancement to CBFM, thereby valorizing an otherwise waste material. Furthermore, the concentrative abilities of CBFM through precipitate and oolitic mineral formation could provide a minable waste product and close the waste-product cycle for DWTW.  相似文献   

Geometallurgical Approach for Implications of Ore Blending on Cyanide Leaching and Adsorption Behavior of Witwatersrand Gold Ores,South Africa     

Nwaila  Glen T.  Ghorbani  Yousef  Becker  Megan  Frimmel  Hartwig E.  Petersen  Jochen  Zhang  Steven 《Natural Resources Research》2020,29(2):1007-1030

Gold production in South Africa is projected to continue its decline in future, and prospects for discovery of new high-grade deposits are limited. Many of the mining companies have resorted to mining and processing low-grade and complex gold ores. Such ores are technically challenging to process, which results in low recovery rates, excessive reagent consumption and high operating costs when compared to free-milling gold ores. In the Witwatersrand mines, options of blending low-grade gold ores with high-grade ores exist. Although it is well known that most of the Witwatersrand gold ores are highly amenable to gold cyanidation, not much is known on the leachability of blended ores, especially the effects of mineralogical and metallurgical variability between different gold ores. In this study, we apply a geometallurgical approach to investigate mineralogical and metallurgical factors that influence the leaching of blended ores in a set of bottle shaker and reactor column tests. Three gold-bearing conglomerate units, so-called reefs, i.e., Carbon Leader Reef, Ventersdorp Contact Reef and the Black Reef, all in the Carletonville goldfield, were sampled. The ores were prepared using a terminator jaw crusher followed by vertical spindle pulverizer (20 kg aliquot) and high-pressure grinding rolls (80 kg aliquot). Mineralogical analysis was conducted using a range of complementary tools such as optical microscopy, QEMSCAN and micro–XCT. The results show that Witwatersrand gold ores are amenable to the process of ore blending. Some of the ores, however, contain impervious inert gangue and reactive ore minerals. Leach solution can only access gold locked in impervious gangue minerals through HPGR-induced pores and/or cracks. The optimum ore blending ratio of the bottle shaker experiments (p80?=???75 μm) comprises 60% Carbon Leader Reef, 20% Ventersdorp Contact Reef and 20% Black Reef and yields 92% recovered Au over a leach period of 40 h. Blended ores with high carbonaceous material (>?1 wt% carbonaceous material, (Black Reef?=?36–60%) yield lower recoveries of 60–69% Au). Ore leaching at the mixed-bed reactor column (??75 μm and ??5.6/+?4 mm) yields about 70% over a leach period of two weeks. We therefore suggest that the feasibility of ore blending is strongly controlled by the mineralogy of the constituent ores and that a mixed-bed reactor may be a viable alternative method for leaching of the low-grade Witwatersrand gold ores. Material from certain reefs, such as the Black Reef, has synergistic/antagonistic (nonadditive) blending effects. The overall implication of this study is that ore blending ratios, effects of comminution on mineral liberation, an association of gold with other minerals, and gold adsorption behavior will greatly inform future technology choices in the area of geometallurgy.

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