Geologic,geomorphic, and meteorological aspects of debris flows triggered by Hurricanes Frances and Ivan during September 2004 in the Southern Appalachian Mountains of Macon County,North Carolina (southeastern USA)

In September 2004, rain from the remnants of Hurricanes Frances and Ivan triggered at least 155 landslides in the Blue Ridge Mountains of North Carolina. At least 33 debris flows occurred in Macon County, causing 5 deaths, destroying 16 homes, and damaging infrastructure. We mapped debris flows and debris deposits using a light-detecting and ranging digital elevation model, remote imagery and field studies integrated in a geographic information system. Evidence of past debris flows was found at all recent debris flow sites. Orographic rainfall enhancement along topographic escarpments influenced debris flow frequency at higher elevations. A possible trigger for the Wayah and fatal Peeks Creek debris flows was a spiral rain band within Ivan that moved across the area with short duration rainfall rates of 150–230 mm/h. Intersecting bedrock structures in polydeformed metamorphic rock influence the formation of catchments within structural–geomorphic domains where debris flows originate.     

Effect of advective mass transfer on field scale fluid and solute movement: Field and modeling studies at a waste disposal site in fractured rock at Oak Ridge National Laboratory, Tennessee, USA

Advective mass transfer is a pore scale mass-transfer process that affects fluid and solute movement between pore domains such as fracture and matrix in a structured porous medium. Mechanistically similar to advection in the advection-dispersion of solutes in non-structured porous medium, it redistributes solutes by moving solute and solvent simultaneously between pore domains. While there is much research on diffusive mass transfer that is often referred to as matrix diffusion, there is a lack of information and study for advective mass transfer in the literature. The objective of this research is to study the effects of advective mass transfer on fluid and solute movement between pore domains. First, field hydraulic measurements at a waste disposal site in fractured rock at Oak Ridge National Laboratory (ORNL), Tennessee, USA, are used to calibrate a fracture-matrix, two-pore-domain groundwater flow model. Latin-hypercube sensitivity analysis suggests that the uncertainty of the calibrated model parameters is small and the calibrated flow model is nearly the optimal. Fracture spacing thus obtained is used to calculate diffusive mass transfer coefficients. The individual effects of advective and diffusive mass transfer on solute movement are then quantitatively evaluated. The calculations indicate that pore structure conceptual models may significantly affect the role of advective mass transfer in field and pore-scale mass transfer. In the particular ORNL field site and with a fracture-matrix pore structure model, contribution of advective mass transfer to solute mass movement is about three to eight orders of magnitude smaller than that of diffusive mass transfer.

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Resumen La transferencia de masa advectiva es un proceso de transferencia de masa en escala intersticial que afecta el movimiento de fluido y soluto entre ámbitos porosos tal como fractura y matriz en un medio estructurado poroso. Este proceso, mecánicamente similar a la advección en la dispersión-advección de solutos de medios porosos no estructurados, redistribuye los solutos mediante el movimiento simultáneo de soluto y solvente entre ámbitos porosos. Mientras que existe bastante investigación en transferencia difusiva de masa que frecuentemente se conoce como difusión en matriz, existe falta de información y estudio de transferencia advectiva de masa en la literatura. El objetivo de esta investigación es estudiar los efectos de la transferencia advectiva de masa en el movimiento de fluido y soluto entre ámbitos porosos. Primero se utilizaron mediciones hidráulicas de campo en un sitio de depósito de residuos en roca fracturada en el Laboratorio Nacional Oak Ridge (ORNL), Tennessee, USA, para calibrar un modelo de flujo de agua subterránea de ámbito de dos poros fractura-matriz. Análisis de sensitividad hipercúbico-latino sugieren que la incertidumbre de los parámetros del modelo calibrado es pequeña y que el modelo de flujo calibrado es aproximadamente el óptimo. El espaciamiento de fracturas así obtenido se utiliza para calcular los coeficientes de transferencia de masa difusiva. Luego se evalúa cuantitativamente los efectos individuales de transferencia de masa advectiva y difusiva en el movimiento de soluto. Los cálculos indican que los modelos conceptuales de estructura porosa pueden afectar significativamente el papel de transferencia de masa advectiva en escalas de campo e intersticial de transferencia de masa. En el sitio de campo específico ORNL y con un modelo de estructura porosa de matriz-fractura, la contribución de transferencia de masa advectiva al movimiento de masa soluto es aproximadamente tres a ocho órdenes de magnitud más pequeño que la contribución por transferencia de masa difusiva.

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Résumé Résumé Le transfert advectif de masse est un processus de transfert de masse à léchelle du pore qui affecte les mouvements du fluide et du soluté entre les différents domaines de pores, tel les fractures et la matrice dans un milieu poreux structuré. Mécaniquement similaire à ladvection dans le concept advection-dispersion de solutés dans les milieux non structurés, ce transfert redistribue les solutés simultanément avec le fluide entre les différents domaines poreux. Alors que de nombreuses recherches portent sur les transferts de masse par diffusion, se référant généralement à une diffusion par la matrice, il y a un grand manquement dinformations et détudes sur les transferts de masse par advection dans la littérature. Lobjectif de cette recherche est détudier leffet du transfert advectif de masse de fluide et de soluté entre les différents domaines poreux. Premièrement, les mesures hydrauliques de terrain sur la décharge en milieu fracturé du laboratoire national dOak Ridge ORNL, Tennessee, USA, sont utilisées pour calibrer un modèle hydrogéologique à double porosité fracture-matrice. Lanalyse de sensibilité latin-hypercube suggère que lincertitude sur les paramètres du modèle est faible et que le calibrage est pratiquement optimal. Lespace de fracture résultant permet de calculer les coefficients de transfert de masse par diffusion. Les effets individuels de ladvection et de la diffusion sur les mouvements de solutés sont dés lors évalués. Les calculs indiquent que le modèle conceptuel de la structure des pores peuvent significativement affectés le rôle du transfert advectif de masse à léchelle du pore et du terrain. Dans le cas du site de lORNL et avec un modèle structuré fracture-matrice, la contribution de ladvection au transfert de masse est de lordre de trois-huitième du transfert de masse par diffusion.

     

Lipid biomarkers and carbon-isotopes of modern travertine deposits (Yellowstone National Park, USA): Implications for biogeochemical dynamics in hot-spring systems

Lipid biomarkers and ¹³C fractionation patterns were used to understand the dynamics of carbon cycling during microbial metabolisms in different environments of travertine precipitation (called facies) at Spring AT-1 on Angel Terrace in the Mammoth Hot Springs complex of Yellowstone National Park, USA. Microbial mats that encrust travertine deposits were collected for analyses of lipid biomarkers and carbon isotopes along the continuous drainage outflow system of Spring AT-1. The spring water exhibits a continuous temperature drop from 71°C in the vent at top to 24°C in the distal slope at bottom. Phospholipid fatty acids (PLFA) and glycolipid fatty acids (GLFA) exhibit distinctly different compositions in each of the facies, which are consistent with partitioning of the bacterial 16S rRNA gene sequences in the Spring AT-1 travertine facies (Fouke et al., 2003).The δ¹³C composition of total biomass within the microbial mats decreases from −16.1‰ in the vent to −23.5‰ in the distal slope. However, lower values occur in the pond (−26.0‰) and the proximal slope (−28.0‰) between the vent and the distal slope. Isotopic compositions of PLFA and GLFA have variations similar to those of total biomass. The average δ¹³C values of PLFA are −12.4 ± 5.2‰ (n = 10 individual fatty acids, same below) in the vent, −33.0 ± 3.1‰ (n = 11) in the pond, −33.7 ± 3.8‰ (n = 16) in the proximal slope, and −22.4 ± 3.4‰ (n = 10) in the distal slope; the average δ¹³C values of GLFA are −19.6 ± 3.0‰ (n = 3) in the vent, −30.4 ± 4.7‰ (n = 8) in the pond, −36.9 ± 2.8‰ (n = 12) in the proximal slope, and −27.9 ± 3.1‰ (n = 13) in the distal slope. In particular, fatty acids in the vent are enriched in ¹³C relative to the total biomass, which is consistent with the notion that the biosynthetic pathways of the extant microbial community in the vent may be dominated by Aquificales using the reversed tricarboxylic acid cycle. Fractionations between fatty acids and total biomass in the pond, the proximal slope and the distal slope suggest the involvement of other biosynthetic pathways for CO₂ fixation by extant microbial populations. The results indicate that lipid biomarkers provide valuable information on the changing diversity and activity of microbial communities in different depositional environments. Carbon-isotope fractionations, on the other hand, can provide insight into the operating biosynthetic pathways associated with different organisms in the changing environment. This integrated approach may serve as a powerful tool for identifying functional metabolism within a community and identify shifts in microbial community structure in modern hot-spring systems.