Holocene records of eolian dust deposition from high-elevation lakes in the Uinta Mountains,Utah, USA

Radiocarbon-dated sediment cores from subalpine lakes were used to investigate post-glacial dust deposition in the Uinta Mountains (Utah, USA). Lake sediments were geochemically characterized with ICP-OES, ICP-MS and XRF core scanning. Collections from passive samplers constrain the properties of modern dust, and samples of regolith constrain properties of the local material within the watershed. Ca and Eu are more abundant in dust, whereas Ti and Zr are more abundant in local regolith. As a result, the Ca/Ti and Eu/Zr ratios are indices for the dust content of lake sediment. In all records, the dust index rises in the early Holocene as watersheds became stabilized with vegetation, reducing the influx of local material. After this point, values remained above average through the middle Holocene, consistent with an increased dust content in the sediment. Dust index values drop in the late Holocene in most lakes, suggesting a decrease in dust abundance. Generally synchronous shifts in dust index values in cores from lakes in different parts of this mountain range are evidence of enhanced dust deposition in this region during the middle Holocene, and are consistent with a variety of records for increased aridity in the south-western USA at this time.     

Chemical and physical characteristics of springs discharging from regional flow systems of the carbonate-rock province of the Great Basin, western United States

The regional carbonate aquifer in the carbonate-rock province of the Great Basin, USA, covers thousands of square kilometers. It is a significant potential source of water for growth in this arid area. Few wells penetrate the carbonate aquifer, so information on water quantity and quality is derived in large part from ‘regional springs’ that discharge from regional interbasin flow systems. For this study, springs in the carbonate-rock province were sampled; their physical, chemical, and isotopic characteristics were compared to those of known regional springs to identify previously unrecognized regional waters using both examination of the data and multivariate statistical analysis. Criteria for comparison included temperature, discharge, ³H activity, carbon isotope values, and ratios of major and trace ions. Of the 18 springs selected for detailed chemical and isotopic sampling, five springs—Hot, Littlefield, Petrified, Saratoga, and Warm (a)—were identified as regional, and one (Monte Neva Hot) was identified as a possible regional spring. Regional springs provide an easy, low-cost means of investigating aquifer properties; identification of regional springs thus increases the ability to understand the regional carbonate aquifer. The techniques applied in this study can also be used in other regional aquifer systems with diverse and complex geology.     

TRACE and Yohkoh Observations of High-Temperature Plasma in a Two-Ribbon Limb Flare

The ability of the Transition Region and Coronal Explorer (TRACE) to image solar plasma over a wide range of temperatures (Te approximately 104-107 K) at high spatial resolution (0&farcs;5 pixels) makes it a unique instrument for observing solar flares. We present TRACE and Yohkoh observations of an M2.4 two-ribbon flare that began on 1999 July 25 at about 13:08 UT. We observe impulsive footpoint brightenings that are followed by the formation of high-temperature plasma (Te greater, similar10 MK) in the corona. After an interval of about 1300 s, cooler loops (Te<2 MK) form below the hot plasma. Thus, the evolution of the event supports the qualitative aspects of the standard reconnection model of solar flares. The TRACE and Yohkoh data show that the bulk of the flare emission is at or below 10 MK. The TRACE data are also consistent with the Yohkoh observations of hotter plasma (Te approximately 15-20 MK) existing at the top of the arcade. The cooling time inferred from these observations is consistent with a hybrid cooling time based on thermal conduction and radiative cooling.     

Optimizing the control of rock failure in servo-controlled laboratory tests

SummaryOptimizing the Control of Rock Failure in Servo-Controlled Laboratory Tests Recent studies of rock failure have been made with a closed loop servo-controlled testing machine. Feedback from the failing specimen is electronically compared with a pre-determined program and the hydraulic system is continuously and automatically adjusted to ensure that feedback and program are coincident. It is suggested that optimum control of rock failure in any laboratory test is achieved when the closed loop feedback represents the most sensitive indicator of failure. Any required experimental output can then be independently monitored. This method was applied to a variety of rock specimens loaded in uniaxial compression using lateral displacement as feedback. It was possible to control the failure of some rocks which had failed explosively in previous tests where the axial displacement had been programmed to increase monotonically.

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ZusammenfassungOptimale Aufzeichnung des Bruchablaufes von Gestein in servo-gesteuerten Laborversuchen Studien zum Bruch von Gesteinsproben wurden kürzlich mit einem elektronisch geregelten Belastungssystem vorgenommen. Bei diesem System werden Meßdaten der über die maximale Bruchverformung hinaus deformierten Probe mit einem vorgegebenen Verformungs-Programm elektronisch verglichen und das hydraulische Belastungs-System wird dementsprechend kontinuierlich geregelt.Ein optimaler Ablauf des Bruchvorganges wird gewährleistet, wenn das Regelsystem durch möglichst feinstufige Meßdaten der Bruchverformung gesteuert wird. Jede gewünschte zusätzliche physikalische Größe kann dann unabhängig davon gemessen werden.Die Meßmethode wurde bei einachsigen Belastungsversuchen von verschiedenen Gesteinsproben angewendet, wobei zur Steuerung des Regelsystems die gemessene Verformung normal zur Belastungsrichtung gewählt wurde. Dabei war es möglich, auch den Bruch solcher Gesteinsproben zu beherrschen, welche bei früheren Versuchen, bei denen der Vorgang aufgrund der Verformung in Belastungsrichtung mit stetigem Verlauf programmiert wurde, explosionsartig geborsten waren.

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RésuméPour un meilleur contrôle de la rupture des roches dans les essais de laboratoire sur machines asservies Des études récentes sur la rupture des roches ont fait usage de machines d'essai asservies.La réponse de l'éprouvette en cours de rupture est comparée électroniquement à un programme fixé à l'avance, et le système hydraulique est ajusté continuellement et automatiquement pour faire coïncider la réponse avec le programme.On suggère que le meilleur contrôle sera obtenu, quel que soit l'essai, si le signal utilisé représente l'indicateur le plus sensible de la progression de la rupture. Toute autre grandeur physique qui est jugée nécessaire peut alors être enregistrée indépendamment.Cette méthode a été appliquée à la compression monoaxiale de diverses roches, en employant comme signal la déformation transversale. On a pu ainsi régulariser la rupture de certaines roches, qui était explosive dans des essais antérieurs où la déformation axiale augmentait suivant un programme monotone.(Dans cet article, la rupture est un processus, comportant notamment la naissance et le développement de fissures, qui ne peut être observé, avec les machines d'essai classiques, à cause de l'explosion due à une libération brutale de l'énergie de déformation emmaganisée dans la presse. Le contrôle de la rupture, au sens anglais, correspond à une régularisation de ce processus. Note de la Rédaction.)

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With 5 Figures     

Climatic soil moisture deficit - climate and soil data integration in a GIS

This paper discusses a GIS based implementation of a model for soil droughtiness assessment evaluating the impact of possible climate change. It focuses, in particular, on the development of a methodology for mapping Available Water Capacity. An assessment of the Soil Drought Susceptibility for Scotland in the year 2030 is made and illustrated with maps and derived statistics.     

The replacement of chrome spinel by chromian valleriite in sulphide-bearing ultramafic rocks in Western Australia

Chromian valleriite occurs as a replacement product of chrome spinel in the Nepean and Perseverance nickel-iron sulphide deposits of Western Australia. Compositions determined for chromian valleriites are variable due to intergrowth with spinel and to substitution of Fe and Ni for Cu. At Perseverance, valleriite, with minor admixed chrome spinel, has a composition expressed by the formula Fe_1.18Cu_0.81Ni_0.01S_2.00·2.03[Mg_0.50Cr_0.37Mn_0.08Fe_0.03Ti_0.01Al_0.01(OH)_2.00]. Nepean valleriites are similarly intergrown with spinel, with the purest chromian valleriites varying in composition from a nickel-poor Fe_1.21Cu_0.78Ni_0.01S_2.00·1-46.[Mg_0.43Cr_0.18Mn_0.05Fe_0.30(OH)₂] to Fe_1.58Cu_0.28Ni_0.15S_2.00·1.79[Mg_0.51Cr_0.30Fe_0.16Ti_0.03(OH)₂]. Conversion of chrome spinel to valleriite is attributed to addition of Cu and S from the breakdown of chalcopyrite, addition of Mg from serpentinising olivine and limited addition of Ni from the breakdown of pentlandite to mackinawite. These processes are thought to occur as post-metamorphic hydrothermal reactions in nickel sulphide ores that have been subjected to high grade regional metamorphism.