Overwash sedimentation associated with a large-scale northeaster

The December 1, 1974 northeaster was a significant event in terms of sediment transport with 20 m³ of sand per meter of dune breach being carried onto the backdune area of Assateague Island, Maryland as overwash. Previous investigators have reported larger transport rates for landfall hurricanes, but this is the largest amount recorded for a winter northeaster. The Ash Wednesday Storm, March 6–8, 1962, was a much larger event, but no quantitative data exists for overwash deposition.The resulting sedimentary deposit can be interpreted by defining sedimentation units. Inverse sediment grading was predominant, but normal grading occurred when the material was monomineralic and the unit totally depositional in nature. The timing of the storm surge was recorded in some sections as a distinctive heavy mineral enrichment in the sediment.     

Flood resilience in paired US–Mexico border cities: a study of binational risk perceptions

Natural Hazards - The present study was done to analyze and compare synoptic conditions during the most durable pollution and clean waves (MDPW and MDCW) in Tehran City (capital of Iran). For this...     

Writing difference differently

This paper investigates the writing of situated knowledge and explores the possibilities of enacting difference by writing differently. We present a selection of research stories in which carrier bags, sounds, baskets, gardens and potatoes are interpreted less as objects of research or metaphors to aid in analysing phenomena, than as mediators of the stories. Our stories emphasise the ontological politics of engaging with and representing the relational, the messy, the spontaneous, the unpredictable, the non‐human and bodily experiences. These stories demonstrate how writing is performative and how it is integral to the production of knowledge.     

A Comparison of Fuzzy AHP and Ideal Point Methods for Evaluating Land Suitability

This article compares two fuzzy approaches to land suitability evaluations, Analytical Hierarchy Process (AHP) and Ideal Point. The methods were evaluated using a case study which models the opportunities for wheat production under irrigation conditions in the north‐western region of Jeffara Plain, Libya. A number of relevant soil and landscape criteria were identified through a review of the literature and their weights specified as a result of discussions with local experts. The results of the Fuzzy AHP showed that the majority of the study area has membership values to the set of suitability between 0.40 and 0.50, while the results of the Ideal Point approach revealed most of the study area to have membership values between 0.30 and 0.40. While the Fuzzy AHP and Ideal Point approaches accommodate the continuous nature of many soil properties and produce more intuitive distributions of land suitabilities values, the Fuzzy AHP approach was found to be better than Fuzzy Ideal Point. This was due to the latter's tendency to be biased towards positive and negative ideal values.     

Momentum Distribution in Solar Flare Processes

We discuss the consequences of momentum conservation in processes related to solar flares and coronal mass ejections (CMEs), in particular describing the relative importance of vertical impulses that could contribute to the excitation of seismic waves (“sunquakes”). The initial impulse associated with the primary flare energy transport in the impulsive phase contains sufficient momentum, as do the impulses associated with the acceleration of the evaporation flow (the chromospheric shock) or the CME itself. We note that the deceleration of the evaporative flow, as coronal closed fields arrest it, will tend to produce an opposite impulse, reducing the energy coupling into the interior. The actual mechanism of the coupling remains unclear at present.     

Platinum–palladium–gold mineralization in the Nkenja mafic–ultramafic body, Ubendian metamorphic belt, Tanzania

Significant and widespread enrichment of platinum, palladium, and gold has been found within the Nkenja mafic–ultramafic body located in southern Tanzania in the central part of the Ubendian metamorphic belt. This body is dominated by partly serpentinized chromitiferous dunite, wehrlite and olivine clinopyroxenite, which are tectonically intercalated with amphibolitized metagabbro. The dunites contain both disseminated and seam-type chrome spinel with an Al-rich composition. The seams are thin, impersistent and, together with enclosing dunite, often show deformation at granulite facies conditions. Forsterite contents of olivine in the dunite range from 87 to 92?mol%. Clinopyroxene in wehrlite and clinopyroxenite is diopsidic with significant contents of Al and Na. Clinopyroxene forms irregular bands and crosscutting veins in the dunite, as well as occurring as weakly dispersed isolated grains in the dunite. Elevated levels of Pt, Pd and Au occur in all ultramafic rocks, but not amphibolitized metagabbro, and there is a weak correlation between high abundances of platinum-group element (PGE) and chromitites. PGE values are erratically distributed and are associated with trace to minor amounts of disseminated sulphides (pyrrhotite, pentlandite, heazlewoodite, chalcopyrite and bornite). The abundances of all PGE are consistently anomalous, suggesting a primary igneous control by sulphides in ultramafic rock. However, there has evidently been a strong metamorphic and/or hydrothermal overprint on what was probably an original magmatic concentration of PGE-bearing sulphides. Geological mapping and petrological evidence, as well as the style of PGE sulphide mineralization, are consistent with the Nkenja ultramafic body being part of the crustal section of a dismembered Palaeoproterozoic ophiolite.     

Algorithm and implementation uncertainty in viewshed analysis

Abstract

In most documentation of geographical information systems (GIS) it is very rare to find details of the algorithms used in the software, but alternative formulations of the same process may derive different results. In this research several alternatives in the design of viewshed algorithms are explored. Three major features of viewshed algorithms are examined: how elevations in the digital elevation model are inferred, how viewpoint and target are represented, and the mathematical formulation of the comparison. It is found that the second of these produces the greatest variability in the viewable area (up to 50 per cent over the mean viewable area), while the last gives the least. The same test data are run in a number of different GIS implementations of the viewshed operation, and smaller, but still considerable, variability in the viewable area is observed. The study highlights three issues: the need for standards and/or empirical benchmark datasets for GIS functions; the desirability of publication of algorithms used in GIS operations; and the fallacy of the binary representation of a complex GIS product such as the viewshed.     

Integrating land-cover data with different ontologies: identifying change from inconsistency

Spatially coincident land-cover information frequently varies due to technological and political variations. This is especially problematic for time-series analyses. We present an approach using expert expressions of how the semantics of different datasets relate to integrating temporal time series land-cover information where the classification classes have fundamentally changed. We use land-cover mapping in the UK (LCMGB and LCM2000) as example data sets because of the extensive object-based meta-data in the LCM2000. Inconsistencies between the two datasets can arise from random, gross and systematic error and from an actual change in land cover. Locales of possible land-cover change are inferred by comparing characterizations derived from the semantic relations and meta-data. Field visits showed errors of omission to be 21% and errors of commission to be 28%, despite the accuracy limitations of the land-cover information when compared with the field survey component of the Countryside Survey 2000.     

Mixed messages in iron oxide–copper–gold systems of the Cloncurry district,Australia: insights from PIXE analysis of halogens and copper in fluid inclusions

Proterozoic rocks of the Cloncurry district in NW Queensland, Australia, are host to giant (tens to hundreds of square kilometers) hydrothermal systems that include (1) barren regional sodic–calcic alteration, (2) granite-hosted hydrothermal complexes with magmatic–hydrothermal transition features, and (3) iron oxide–copper–gold (IOCG) deposits. Fluid inclusion microthermometry and proton-induced X-ray emission (PIXE) show that IOCG deposits and the granite-hosted hydrothermal complexes contain abundant high temperature, ultrasaline, complex multisolid (type 1) inclusions that are less common in the regional sodic–calcic alteration. The latter is characterized by lower salinity three-phase halite-bearing (type 2) and two-phase (type 3) aqueous inclusions. Copper contents of the type 1 inclusions (>300 ppm) is higher than in type 2 and 3 inclusions (<300 ppm), and the highest copper concentrations (>1,000 ppm) are found both in the granite-hosted systems and in inclusions with Br/Cl ratios that are consistent with a magmatic source. The Br/Cl ratios of the inclusions with lower Cu contents are consistent with an evaporite-related origin. Wide ranges in salinity and homogenization temperatures for fluid inclusions in IOCG deposits and evidence for multiple fluid sources, as suggested by halogen ratios, indicate fluid mixing as an important process in IOCG genesis. The data support both leaching of Cu by voluminous nonmagmatic fluids from crustal rocks, as well as the direct exsolution of Cu-rich fluids from magmas. However, larger IOCG deposits may form from magmatic-derived fluids based on their higher Cu content.