On the Problem of Sample Preservation by Freezing

During routine analysis of running water samples differences of the analytical results of water‐soluble anions were observed between analysis carried out immediately after sampling and after storage of the cooled/frozen sample. This phenomenon was investigated for some years with the “model ion” chloride. A high number of samples (ca. 210) were analysed over three years with different analytical methods, and by alteration of the sample containers the discrete physical influence of the wall effect of the sample vessel could be worked out definitely. No significant differences occur with the mean value of the year but the single values have high differences in the positive or negative direction. Assuming a similar behaviour of other water constituents when preserved by freezing the analytical values had to be looked at very critically.     

Consequences of forest fires on the hydrogeological response of mountain catchments: a case study of the Riale Buffaga,Ticino, Switzerland

The debris flow of 28 August 1997 which occurred in the Riale Buffaga, a torrent channel in the territory of the village of Ronco s./Ascona (Ticino, Switzerland), has been simulated with a good degree of reliability due to the existence of morphologic surveys of the torrent channel preceding the flood event and the presence of a rain gauge that registered the rainfall event at a resolution of 10 minutes. With these data it is possible to conduct a quantitative analysis of the effect of a forest fire on the hydrogeological response of a given catchment. In the case at hand, a 10‐year rainfall event caused a 100‐ to 200‐year flood event. This result clearly quantifies the possible consequences of a forest fire in terms of territorial safety. Copyright © 2003 John Wiley & Sons, Ltd.     

Local seismic hazard assessment in areas of weak to moderate seismicity—case study from Eastern Germany

Generally the seismic hazard of an area of interest is considered independent of time. However, its seismic risk or vulnerability, respectively, increases with the population and developing state of economy of the area. Therefore, many areas of moderate seismic hazard gain increasing importance with respect to seismic hazard and risk analysis. However, these areas mostly have a weak earthquake database, i.e., they are characterised by relative low seismicity and uncertain information concerning historical earthquakes. In a case study for Eastern Thuringia (Germany), acting as example for similar places in the world, seismic hazard is estimated using the probabilistic approach. Because of the lack of earthquakes occurring in the recent past, mainly historical earthquakes have to be used. But for these the actual earthquake sources or active faults, needed for the analysis, are imprecisely known. Therefore, the earthquake locations are represented by areal sources, a common practice. The definition of these sources is performed carefully, because their geometrical shape and size (apart from the earthquake occurrence model) influence the results significantly. Using analysis tools such as density maps of earthquake epicentres, seismic strain and energy release support this. Oversizing of areal sources leads to underestimation of seismic hazard and should therefore be avoided. Large location errors of historical earthquakes on the other hand are represented by several alternative areal sources with final superimposition of the different results. In a very similar way information known from macroseismic observations interpreted as source rather than as site effects are taken into account in order to achieve a seismic hazard assessment as realistic as possible. In very local cases the meaning of source effects exceeds those of site effects very likely. The influence of attenuation parameter variations on the result of estimated local seismic hazard is relatively low. Generally, the results obtained by the seismic hazard assessment coincide well with macroseismic observations from the thoroughly investigated largest earthquake in the region.     

Pb/Pb and U/Pb zircon dating of subvolcanic rhyolite as a time marker for Hercynian granite magmatism and Sn mineralisation in the Eibenstock granite, Erzgebirge, Germany: Considering effects of zircon alteration

Tin mineralisation is closely related to rhyolite stocks and dykes which occur in the endo- and exocontact of the Eibenstock granite, Erzgebirge, Germany. The same structures which cut the granite control the rhyolite emplacement and the location of ore-bearing greisen bodies. Albitisation and greisenisation related to tin mineralisation as well as sericitisation and argillic alteration may be traced by changes in chemical and mineralogical composition of both rhyolite and granite wall rock. Comprehensive zircon studies by scanning electron microscopy (secondary and backscattered electron as well as cathodoluminescence imaging; EDX measurements) reveal that zircon from rhyolite and from the enclosing granite shows significant changes in chemical composition and crystallinity, including distortion of the U-Pb isotope system when affected by greisenisation. Single evaporation analysis of zircon from rhyolite with little or no greisenisation gave a ²⁰⁷Pb/²⁰⁶Pb age of 290±5 Ma, whereas zircon from little altered granite gave a ²⁰⁷Pb/²⁰⁶Pb age of 320±8 Ma. The single evaporation age of zircon from rhyolite is confirmed by ²³⁸U/²⁰⁶Pb SHRIMP ages of 297±8 Ma. The significant time gap of at least 20 Ma between granite intrusion and rhyolite formation suggests that the late magmatic evolution of the Eibenstock granite cannot be regarded as a source for tin-ore forming fluids as previously assumed.     

On the Exchange of NO3 Radicals with Aqueous Solutions: Solubility and Sticking Coefficient

The exchange of NO₃ radicals with the aqueous-phase was investigated at room temperature (293 K) in a series of wetted denuders. From these experiments, the uptake coefficient of NO₃ was determined on 0.1 M NaCl solutions and was found to be (NO₃) 2 × 10^-3 in good agreement with recent studies. The Henry coefficient of NO₃ was estimated to be K_H(NO₃) = 1.8 M · atm^-1, with a (2) uncertainty of ±3 M · atm^-1. From the upper limit for the Henry coefficient (K_H = 5 M · atm^-1) and available thermodynamic data, the redox potential of dissolved NO₃/NO ₃ ^– is estimated to be in the range of 2.3 to 2.5 V. This range is at the lower boundary of earlier estimates. The results are discussed in the light of a recent publication. Based on our data and a model of the transport and chemistry in the liquid film, an upper limit is derived for the product of the Henry coefficient K_H and the rate coefficient k ₁₀ of the potential reaction NO₃ + H₂O HNO₃ + OH. For K_H = 0.6 M · atm^-1, we find k ₁₀ < 0.05 s^-1 · atm^-1, i.e., about 100 times smaller than what was suggested by Rudich and co-workers. Because of its small solubility, heterogeneous removal of NO₃ is only important under conditions where the dissolved NO₃ is removed quickly from equilibrium, for example by reactions with Cl^– or HSO ₃ ^– ions in the liquid-phase. Otherwise, heterogenous removal should mainly proceed via N₂O₅.     

The petrogenesis of Tertiary cone-sheets in Ardnamurchan, NW Scotland: petrological and geochemical constraints on crustal contamination and partial melting

Abundant cone sheets form one of the last magmatic stages in the Tertiary central complex on the Scottish peninsula of Ardnamurchan and can be grouped into a younger inner and an older outer suite relative to a gabbro intrusion. Most of the cone-sheets consist of tholeiitic to transitional basalt with MgO contents between 7.5% and 4%, although more evolved rocks also occur (to 0.5% MgO). The mafic samples are slightly enriched in the light rare earth elements (Chondrite-normalized La/Sm ∼1.1), the enrichment increases in the more evolved rocks. The compositional variation of the basaltic rocks is mainly due to crystal fractionation of olivine and clinopyroxene at depths of ∼10 km but trace elements show simultaneous assimilation of Archean Lewisian granulite crust. The andesitic to rhyolitic lavas formed by fractional crystallization from the contaminated basaltic magma coupled with assimilation of Proterozoic Moine metasediments at uppermost crustal levels. The occurrence of composite cone-sheets with basaltic and rhyolitic parts and mixtures between these magmas implies that the melts ascended successively but within a short period of time. The parental magmas of the Ardnamurchan cone-sheets must have formed at relatively shallow depths in the mantle and are comparable to the youngest tholeiitic lavas from the neighbouring island of Mull. Received: 5 June 1997 / Accepted: 12 November 1997     

Sedimentology and facies of the meadfoot beds (Lower Devonian) in South-East Devon (England)

Summary The Lower Devonian Meadfoot Group on the east coast of South Devon represents a typical shallow-water facies, comprising a variable sequence of mudstones, siltstones and sandstones or sandy siltstones. Many features of the deposits indicate the influence of strong water movements: cross-lamination, ripple-drift lamination, erosion channels and other washout structures.Current directions have been measured for all the sedimentary structures. Most of the clastic material was carried by lateral transport in this part of the Variscan geosyncline in directions both from W to E and E to W; a polarity of flow which may be explained as due to tidal influence. The direction of slumping indicates a sea floor sloping towards the south or south-west.An interesting feature is the presence of ball-and-pillow structures which is explained as essentially due to a sagging process.Many trails of organisms in the form of burrows occur in pelitic or silty deposits.

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Zusammenfassung Die unterdevonischen Meadfoot Beds, die an der Ostküste von SE-Devonshire ausstreichen, sind in einer typischen Flachwasser-Fazies entwickelt. Sie bestehen aus einer Serie von Tonschiefern, Siltsteinen, Sandsteinen und Sand-Siltsteinen. Eine Reihe von Sedimentstrukturen beweist den Einfluß von stärkeren Wasserbewegungen auf das Ablagerungsbild, wie z. B. Schrägschichtung, Rippelstrukturen, Erosions-Rinnen und andere Auswaschungs-Strukturen.Die Strömungsrichtungen wurden an Hand der verschiedenen Sedimentstrukturen gemessen und ausgewertet. Sie zeigen, daß in diesem Teil des nördlichen Außenrandes der variszischen Geosynklinale der Transport des klastischen Materials vorwiegend durch E-W- oder W-E-Strömungen erfolgte. Diese Polarität wird durch Gezeiten-Wirkung erklärt. Subaquatische Rutschungen deuten auf einen Abfall des Meeresbodens während jener Zeit nach S oder SW.Ein interessantes Phänomen stellen ball-and-pillow-Strukturen dar, die auf komplizierte Sackungs-Bewegungen, vermutlich unter Mitwirkung thixotroper Vorgänge, zurückgehen und vielleicht durch Erdbeben ausgelöst wurden.Lebensspuren, wie Grab- und Borgänge, treten häufig auf, vorwiegend in pelitischem Material oder Siltsteinen.

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Résumé Les Meadfoot-Beds, d'âge éodévonien, qui affleurent sur la côte orientale du Devonshire sud-oriental, présentent un faciès néritique typique. Ces assises sont constituées de schistes, d'aleurites, de grès et de grès aleuritiques. Les structures sédimentaires font valoir une eau fortement agitée pendant le dépôt des sédiments; ainsi on note des stratifications obliques, des ripples-marks, des sillons d'érosion et d'autres indices de taraudage.Le sens des courants a été déterminé à l'aide de différentes structures sédimentaires. Il démontre que dans cette partie du bord septentrional du géosynclinal varisque le matériel clastique était transporté surtout par des courants EW et WE. Cette polarité se laisse expliquer par les effets de la marée. Les glissements subaquatiques suggèrent une pente du fond marin vers le S ou vers le SW.Les structures «ball and pillow» présentent un phénomène intéressant, qui se laisse ramener à des tassements, qui vont probablement de pair avec des procès de thixotropie, et qui sont peut-être occasionnés par des tremblements de terre.Les traces de vie, telles que des pistes d'excavation ou de fouissement, sont nombreuses surtout dans le matériel pélitique.

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A resonance-fluorescence instrument for the in-situ measurement of atmospheric carbon monoxide

The development of an airborne instrument for the in-situ measurement of carbon monoxide is described. The technique is resonance-fluorescence of the (A ¹ X ¹) transition of CO in the VUV. The instrument achieves a detection limit of 1 ppb for an interaction time of 10 s from ground level up to an altitude of 34 km. Interferences from other stratospheric trace gases are negligible.