Bombs behaving badly: unexpected trajectories and cooling of volcanic projectiles     

Lo?c Vanderkluysen  Andrew J. L. Harris  Karim Kelfoun  Costanza Bonadonna  Maurizio Ripepe 《Bulletin of Volcanology》2012,74(8):1849-1858

We collected thermal infrared video of two explosive eruptions at Stromboli in June 2008 and manually traced the trajectories of 95 particles launched during two eruptions. We found that 10–15?% of the analyzed trajectories deviated from predicted curves due to collisions, causing one particle to travel horizontally more than twice as far as expected. Furthermore, we observed an oscillatory cooling behavior for the airborne pyroclasts, with a median period of 0.46?s. Measured cooling was typically much faster than model-predicted cooling with discrepancies of up to 40?% between measured cooling and theoretical modeling. We interpret the measured cooling curves as resulting from the spinning and twisting and tearing of particles during travel: the periodic re-exposing of the hotter core of the pyroclasts to the atmosphere may cause the observed oscillations, and the spinning may accelerate cooling by enhancing convective heat transfer. Current volcanic trajectory and cooling models do not account for projectile collisions, spinning, or tearing and can thus severely underestimate the maximum landing distance and cooling rates of large pyroclasts.  相似文献   

Chemical Immobilization of Lead,Cadmium, Copper,and Nickel in Contaminated Soils by Phosphate Amendments   总被引：1，自引：0，他引：1       下载免费PDF全文

Mahnoosh Valipour  Karim Shahbazi  Ali Khanmirzaei 《洁净——土壤、空气、水》2016,44(5):572-578

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Pyroclastic flow erosion and bulking processes: comparing field-based vs. modeling results at Tungurahua volcano,Ecuador     

Julien Bernard  Karim Kelfoun  Jean-Luc Le Pennec  Silvia Vallejo Vargas 《Bulletin of Volcanology》2014,76(9):1-16

Pyroclastic density currents (PDCs) are high-temperature and high-velocity mixtures that threaten populations in the vicinity of many active volcanoes. Deciphering the cause of their remarkable mobility is essential for volcanic hazard analysis, but remains difficult because of the complex processes occurring within the flows. Here, we investigate the effect of bulking on dense PDC mobility by means of a double approach. First, we estimate the amount of material incorporated into scoria flows emplaced during the August 2006 eruption of Tungurahua volcano, Ecuador. For this, we carry out a detailed analysis of 3D-corrected digital images of well-exposed scoria flow deposits. Componentry analysis indicates that PDC bulking occurs principally on the steep (>25°) upper slope of the volcano, and the deposits typically comprise 40–50 wt% of non-juvenile (i.e., accessory and accidental) material. Secondly, we develop a simple stress-related grain-by-grain equation of erosion combined with two simple depth-averaged geophysical mass-flow models that compare the bulking mechanism to a non-fluidized and a fluidized flow. Two behaviors based on Coulomb and plastic rheologies are used to reproduce, on a first order basis, the 2006 Tungurahua PDCs. Cross-check comparisons between these modeled cases and the erosion pattern inferred from field-based data allow us to evaluate the accuracy of our modeling assumptions. Regardless of the rheological regime, the PDC-induced erosion pattern of the 2006 Tungurahua eruption can only be reproduced by fluctuations of the flow’s basal shear stress during emplacement. Such variations are controlled by flow thinning-thickening processes, notably through the formation of a thick non-erosive flow body that pushes a thin frictional erosive front during PDC emplacement. The input volume of juvenile material, as well as the thickness of the erodible layer available prior to the eruption, are additional key parameters. Our work highlights complexities in PDC erosion and bulking processes that deserve further study. In terms of hazard assessment, our findings reveal that incorporation and bulking translate into increased flow mobility, i.e., the augmented flow mass enhances both flow velocity and runout distance (up to 20 %). These outcomes should be considered closely for hazard analysis at many other andesitic volcanoes worldwide where similar PDC events are common.  相似文献   

Human virus and microbial indicator occurrence in public-supply groundwater systems: meta-analysis of 12 international studies     

G.?Shay?FoutEmail author  Mark?A.?Borchardt  Burney?A.?KiekeJr  Mohammad?R.?Karim 《Hydrogeology Journal》2017,25(4):903-919

Groundwater quality is often evaluated using microbial indicators. This study examines data from 12 international groundwater studies (conducted 1992–2013) of 718 public drinking-water systems located in a range of hydrogeological settings. Focus was on testing the value of indicator organisms for identifying virus-contaminated wells. One or more indicators and viruses were present in 37 and 15% of 2,273 samples and 44 and 27% of 746 wells, respectively. Escherichia coli (E. coli) and somatic coliphage are 7–9 times more likely to be associated with culturable virus-positive samples when the indicator is present versus when it is absent, while F-specific and somatic coliphages are 8–9 times more likely to be associated with culturable virus-positive wells. However, single indicators are only marginally associated with viruses detected by molecular methods, and all microbial indicators have low sensitivity and positive predictive values for virus occurrence, whether by culturable or molecular assays, i.e., indicators are often absent when viruses are present and the indicators have a high false-positive rate. Wells were divided into three susceptibility subsets based on presence of (1) total coliform bacteria or (2) multiple indicators, or (3) location of wells in karst, fractured bedrock, or gravel/cobble settings. Better associations of some indicators with viruses were observed for (1) and (3). Findings indicate the best indicators are E. coli or somatic coliphage, although both indicators may underestimate virus occurrence. Repeat sampling for indicators improves evaluation of the potential for viral contamination in a well.  相似文献   

Syncline contribution to mountain peak building: examples from Western Zagros,Kurdistan Region,Northeastern Iraq     

Kamal Haji Karim  Polla Azad Khanaqa 《Arabian Journal of Geosciences》2017,10(16):375

The current study focuses on roles of the synclines in building mountains of the Zagros Fold-Thrust Belt from Northeastern Iraq, Kurdistan Region. The studied area is located in the Imbricated Zone, which is a continuation of Simply Folded Zone of Iran. In some parts of this zone, the synclines contribute to building nearly half of the mountains and increase the relief contrast of the landscapes. The role of syncline in building mountains is opposite to its apparent intrinsic shape which is located in low land and normally forms synclinal valleys. In studied area, this phenomenon is observable in the areas that are complexly deformed, deeply exhumed, and predominately composed of the carbonate rocks. In these areas, exhumation and stream erosion have removed high thickness of overburden rocks and the tectonic stresses have crenulated carbonate rocks in the synclines. Due to these processes, these synclines are observable on the peak of the mountains now. The contribution of synclines in mountain building is related to three properties: the first is folding of synclines in confined condition (relative to anticlines) by which they have transformed to highly compact and stiff rocks. The second is accumulation of hydrothermal or meteoric water in the synclines due to its downward bending which aids precipitation of minerals and heals the possible tectonically and lithostatically induced fractures. The third is ductile deformation of synclines in confined and deeper level as compared to brittle deformation of anticlines in relatively shallower level and unconfined condition during deformation. Consequently, these factors result in an inversion of topography by which synclines are remained as mountains (high topography) above surface during exhumation while erosion removes anticlines. The result of this study is applicable for geological, geomorphological, and structural mapping in highly deformed and deeply exhumed terrains. The possible prediction of geomorphological position of synclines and anticlines on the mountain peaks and valley bottoms respectively is the applicable result in the above terrains.  相似文献   

Runout of the Socompa volcanic debris avalanche, Chile: a mechanical explanation for low basal shear resistance   总被引：1，自引：0，他引：1  

Tim Davies  Mauri McSaveney  Karim Kelfoun 《Bulletin of Volcanology》2010,72(8):933-944

We propose a mechanical explanation for the low basal shear resistance (about 50 kPa) previously used to simulate successfully the complex, well-documented deposit morphology and lithological distribution produced by emplacement of the 25 km³ Socompa volcanic debris avalanche deposit, Chile. Stratigraphic evidence for intense basal comminution indicates the occurrence of dynamic rock fragmentation in the basal region of this large granular mass flow, and we show that such fragmentation generates a basal shear stress, retarding motion of the avalanche, that is a function of the flow thickness and intact rock strength. The topography of the Socompa deposit is realistically simulated using this fragmentation-derived resistance function. Basal fragmentation is also compatible with the evidence from the deposit that reflection of the avalanche from topography caused a secondary wave that interacted with the primary flow.  相似文献   

A coupled numerical model for simulation of wave breaking and hydraulic performances of a composite seawall     

Mohammed Fazlul Karim  Tawatchai Tingsanchali   《Ocean Engineering》2006,33(5-6):773-787

A numerical model is developed by combining a porous flow model and a two-phase flow model to simulate wave transformation in porous structure and hydraulic performances of a composite type low-crest seawall. The structure consists of a wide submerged reef, a porous terrace at the top and an impermeable rear wall. The porous flow model is based on the extended Navier-Stokes equations for wave motion in porous media and k−ε turbulence equations. The two-phase flow model combines the water domain with the air zone of finite thickness above water surface. A unique solution domain is established by satisfying kinematic boundary condition at the interface of air and water. The free surface advection of water wave is modeled by the volume of fluid method with newly developed fluid advection algorithm. Comparison of computed and measured wave properties shows reasonably good agreement. The influence of terrace width and structure porosity is investigated based on numerical results. It is concluded that there exist optimum value of terrace width and porosity that can maximize hydraulic performances. The velocity distributions inside and in front of the structure are also investigated.  相似文献   

Simulating the effects of land use changes on soil erosion using RUSLE model   总被引：3，自引：0，他引：3  

Ataollah Kavian  Samaneh Hoseinpoor Sabet  Karim Solaimani  Behnoosh Jafari 《国际地球制图》2017,32(1):97-111

The aim of this paper is to evaluate the impacts of land use change on soil loss. Soil loss was quantified using the revised universal soil loss equation model in Darabkola catchment. Land use maps of 1992, 1998 and 2012 were derived from Landsat Thematic Mapper data. The mean annual soil loss was therefore determined for these years. The results showed open-canopy forest area decreased by 36% between 1992 and 1998. Likewise, the decreasing trend of forest lands which are near to residential areas has continued from 1795 ha in 1998 to 1765 ha in 2012. Also the results indicate that the maximum annual soil loss ranged from 5.06, 6.19 and 15.23 ton h^?1 y^?1 in 1992, 1998 and 2012, respectively. Also, by assuming that all watershed conditions and land uses be constant in the future, then the area of close- and open-canopy forest and dry agricultural lands will be 23.23, 2.88 and 29.89 ha in 2040, respectively.  相似文献   

Monitoring of selected pharmaceuticals over 3 years in a detrital aquifer during artificial groundwater recharge     

Lucila Candela  Karim Tamoh  Iñaki Vadillo  Javier Valdes-Abellan 《Environmental Earth Sciences》2016,75(3):244

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Permeability determination of porous media using large‐scale finite elements and iterative solver     

M. R. Karim  K. Krabbenhoft  A. V. Lyamin 《国际地质力学数值与分析法杂志》2014,38(10):991-1012

The problem of finite element simulation of incompressible fluid flow in porous medium is considered. The porous medium is characterized by the X‐ray microtomography technique in three dimensions. The finite calculus‐based stabilization technique is reviewed to implement the equal order finite element interpolation functions for both velocity and pressure. A noble preconditioner, the nodal block diagonal preconditioner, is considered whose performance is thoroughly investigated. Combining this preconditioner with a standard iterative solver during the computational homogenization procedure, it is possible to carry out the large‐scale fluid flow simulation for estimating permeability of the porous medium with reasonable accuracy and reliability. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献