The Risk Atlas of Mexico City,Mexico: a tool for decision-making and disaster prevention

Natural Hazards - We present a Risk Atlas of Mexico City based on a Geographical Information System (RA-GIS). We identified the prevalent social risk to the more relevant hazards in Mexico City...     

Reconstruction of catastrophic outburst floods of the Diexi ancient landslide-dammed lake in the Upper Minjiang River,Eastern Tibetan Plateau

Natural Hazards - Landslide-dammed lake outburst floods (LLOFs) may pose serious safety threats to nearby residents and their livelihoods, as well as cause major damages to the downstream areas in...     

Hydrogeological investigation of mud-mound springs developed over a weathered basalt aquifer on the Liverpool Plains,New South Wales,Australia

The growth and collapse of mud mounds at a site on the Liverpool Plains in northern New South Wales, Australia has been observed over a 12-year period. The mud mounds appeared in a flat field for the first time in living memory in 1989, but their prior existence in the early Holocene is indicated by archaeological data. The piezometric head in bores drilled through a 7-m bed of clayey silt and screened in weathered basalt at a depth of 8 m was more than 2 m above ground level. Clay has been carried in suspension by water seeping to the ground surface where it has accumulated and formed a mound. Approximately eight years after their initial appearance, the growth of the mounds stopped and within a further three years they had almost completely disappeared.Mechanisms for the growth and decay of the mounds are reviewed. The chemistry of the shallow bore water and the water seeping from the surface of the mounds was dominated by sodium bicarbonate with a 4 mEq/l increase between the weathered basalt and the surface of the mound. Inverse modelling (PHREEQC) is used to determine possible chemical reactions that can account for this increase.

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Electronic Supplementary Material Supplementary material is available in the online version of this article at http://dx.doi.org/10.1007/s10040-003-0278-0.

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Resumen Se ha observado durante 12 años el crecimiento y el colapso de montículos de lodo en un emplazamiento ubicado en las Llanuras de Liverpool, en el estado australiano de Nueva Gales del Sur. Según la memoria existente, los montículos de lodo aparecieron en un campo llano por vez primera en 1989, pero, por datos arqueológicos, se conoce de su existencia a comienzos del Holoceno. Los niveles piezométricos en sondeos perforados a través de 7 m de limos arcillosos y ranurados en el basalto meteorizado a 8 m son superiores en más de 2 m a la superficie del terreno. La arcilla es portada en suspensión por el agua que descarga hacia la superficie del terreno, donde se acumula y forma el montículo. Unos 8 años después de su aparición, el crecimiento de los montículos se detiene y éstos acaban prácticamente desapareciendo en otros 3 años.Se revisa los mecanismos que originan el crecimiento y desaparición de los montículos. La química de las aguas someras de los sondeos y del agua que se filtra desde la superficie de los montículos está dominada por bicarbonato sódico, con un incremento de 4 meq/L entre el basalto meteorizado y la superficie del montículo. Se utiliza la modelación inversa (PHREEQC) para determinar las reacciones químicas que pueden explicar dicho aumento.

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Résumé La croissance et l'effondrement de monticules de vase situés dans les plaines de Liverpool, dans le nord des Nouvelles Galles du Sud, ont été observés pendant 12 ans. Les monticules de vase sont apparus en terrain plat pour la première fois de mémoire d'homme en 1989; mais leur existence antérieure dès le début de l'Holocène est attesté par des données archéologiques. Le niveau piézométrique dans des forages traversant 7 m de silt argileux et recouvrant un basalte altéré à 8 m était de plus de 2 m au-dessus de la surface du sol. L'argile a été apportée en suspension par l'eau suintant à la surface du sol où elle s'est accumulée pour former un monticule. Environ 8 ans après leur première apparition, la croissance des monticules s'est arrêtée et ils ont presque complètement disparu dans les 3 ans qui ont suivi.Les mécanismes de croissance et de régression de ces monticules sont passés en revue. La chimie de l'eau des forages à proximité de la surface et de l'eau filtrant à la surface des monticules était dominée par le bicarbonate de sodium, avec une augmentation de 4 meq/l entre le basalte altéré et la surface du monticule. Une modélisation inverse (PHREEQC) a été mise en uvre pour déterminer les réactions possibles pouvant rendre compte de cet accroissement.

     

The Role of a PhD Field Exam in Preparing Graduate Students for Academic Careers*

The Department of Geography at Arizona State University implemented a field exam as part of its PhD program requirements. This field exam requires students to develop an independent field‐based research project based on a general question in the student's specialty area. A survey of current and former PhD students and faculty members document how the field exam assists students in developing skills necessary for continuing graduate research and for preparing them for the rigors of academic employment. The outcomes of the exam include both long‐term, process‐related benefits and more immediate tangible rewards. For some students, the preliminary fieldwork and results redirect student interests and form the basis for their eventual dissertation. The field exam is adaptable to a diversity of geography research methods, subject areas, and graduate degree programs, while remaining grounded in the discipline's vibrant, widely respected fieldwork tradition.     

The Greenland Ice Core Chronology 2005, 15–42 ka. Part 1: constructing the time scale

The Greenland Ice Core Chronology 2005, GICC05, is extended back to 42 ka b2k (before 2000 AD), i.e. to the end of Greenland Stadial 11. The chronology is based on independent multi-parameter counting of annual layers using comprehensive high-resolution measurements available from the North Greenland Ice Core Project, NGRIP. These are measurements of visual stratigraphy, conductivity of the solid ice, electrolytical melt water conductivity and the concentration of Na⁺, Ca²⁺, SO₄²⁻, NO₃⁻, NH₄⁺. An uncertainty estimate of the time scale is obtained from identification of ‘uncertain’ annual layers, which are counted as 0.5±0.5 years. The sum of the uncertain annual layers, the so-called maximum counting error of the presented chronology ranges from 4% in the warm interstadial periods to 7% in the cold stadials. The annual accumulation rates of the stadials and interstadials are on average one-third and half of the present day values, respectively, and the onset of the Greenland Interstadials 2, 3, and 8, based on 20 year averaged δ¹⁸O values, are determined as 23,340, 27,780, and 38,220 yr b2k in GICC05.     

Cd, Cr, Cu, Ni and Pb in the water column and sediments of the Ob-Irtysh Rivers, Russia

Concentrations of Cd, Cr, Cu, Ni and Pb were determined in filtered water, suspended particulate matter, and bottom sediments from a 2000 km section of the Ob and Irtysh Rivers. Dissolved Cd, Cr, Cu and Ni concentrations are similar to, or higher than, results from other Russian Arctic and large world river-estuaries. Concentrations of Cd, Cr, Cu, Ni and Pb in suspended particulate matter are generally comparable to results from other Russian Arctic and large world rivers and estuaries. Comparison of trace metal ratios in crustal material and suspended particulate matter and bottom sediment suggests that the source of Cr, Cu and Ni is continental weathering. Particulate Cd and Pb are elevated relative to their crustal abundance, suggesting a source of these metals to the Ob-Irtysh in addition to continental weathering.     

Ore textures within the U lens of the Navan Zn-Pb deposit, Ireland

Recent exploration in the vicinity of the giant (>90 Mt) Navan orebody has resulted in the discovery of ore-grade mineralisation to the southwest of the deposit, much of which occurs within the Upper Pale Beds, a horizon that is only weakly mineralised above the main orebody. Within this new U lens, mineralisation preferentially occurs within bioclastic carbonate grainstones and calcareous quartz sandstones, and is dominated by sulphide replacement of the carbonate component of the host sequence. Much of the replacive mineralisation is spatially associated with hydrothermal cavities, which are filled by a variable mixture of brecciated replacement sulphide minerals, space-filling sulphide and gangue cements, and internal sediments. Mineralisation also occurs within veins and dissolution seams, and as disseminated sulphide minerals. Massive mineralisation is typically a complex, chaotic, combination of replacement, cavity, and fracture-filling sulphides. Fluid inclusion analyses of ore-stage saddle dolomite indicate temperatures at the time of sulphide precipitation of ~90–150 °C, with a maximum of 175 °C. These temperatures are lower than those typically proposed for Irish-type deposits.     

Contrasting water management techniques in Tunisia: towards sustainable agricultural use

Tunisia is a marginal country hydrologically and it has adopted a number of distinctive methods of water management for agriculture. The central region supports modern dam irrigation, whilst traditional rainwater harvesting is practiced in the south. These contrasting techniques are described and evaluated in terms of sustainability using empirical field data and secondary literature for two study sites. Research focuses primarily on the physical environment, but socio-cultural and economic viability are also examined. Analysis indicates that traditional water management advantageously partitions the continuum dividing hazards and resources through subtle manipulation of the environment. A potentially hazardous environment is rendered secure by resourceful water management based on community action and cumulative knowledge. This practice minimizes community dependency and local economic imbalance. With dam irrigation, carrying capacity is established more forcibly by centralized control in order to place society within world markets. An almost total break from environmental variability is made in the short term, but this can lead to disequilibrium over longer durations. Additionally, the spatial and social distributions of development are uneven. In Tunisia, maintenance of traditional methods can reduce the negative impacts caused by modern programmes and support their positive characteristics. A mix of both methods offers a foundation to sustainable water supply in the new millennium.     

Diatoms as indicators of climatic and limnological change in Swedish Lapland: a 100-lake calibration set and its validation for paleoecological reconstructions

This study investigated the distribution of subfossil diatom assemblages in surficial sediments of 100 lakes along steep ecological and climatic gradients in northernmost Sweden (Abisko region, 67.07° N to 68.48° N latitude, 17.67° E to 23.52° E longitude) to develop and cross-validate transfer functions for paleoenvironmental reconstruction. Of 19 environmental variables determined for each site, 15 were included in the statistical analysis. Lake-water pH (8.0%), sedimentary loss-on-ignition (LOI, 5.9% and estimated mean July air temperature (July T, 4.8%) explained the greatest amounts of variation in the distribution of diatom taxa among the 100 lakes. Temperature and pH optima and tolerances were calculated for abundant taxa. Transfer functions, based on WA-PLS (weighted averaging partial least squares), were developed for pH (r² = 0.77, root-mean-square-error of prediction (RMSEP) = 0.19 pH units, maximum bias = 0.31, as assessed by leave-one-out cross-validation) based on 99 lakes and for July T (r² = 0.75, RMSEP = 0.96 °C, max. bias = 1.37 °C) based on the full 100 lake set. We subsequently assessed the ability of the diatom transfer functions to estimate lake-water pH and July T using a form of independent cross-validation. To do this, the 100-lake set was divided in two subsets. An 85-lake training-set (based on single limnological measurements) was used to develop transfer functions with similar performance as those based on the full 100 lakes, and a 15-lake test-set (with 2 years of monthly limnological measurements throughout the ice-free seasons) was used to test the transfer functions developed from the 85-lake training-set. Results from the intra-set cross-validation exercise demonstrated that lake-specific prediction errors (RMSEP) for the 15-lake test-set corresponded closely with the median measured values (pH) and the estimations based on spatial interpolations of data from weather stations (July T). The prediction errors associated with diatom inferences were usually within the range of seasonal and interannual variability. Overall, our results confirm that diatoms can provide reliable and robust estimates of lake-water pH and July T, that WA-PLS is a robust calibration method and that long-term environmental data are needed for further improvement of paleolimnological transfer functions.