Long-term erosion on granitic roadcuts based on exposed tree roots

Exposed roots were used to estimate soil and bedrock erosion on the cut slopes of a 45-year-old road constructed in granitic soils of the Idaho Batholith. The original roadcut surface was defined by projecting a straight line from the toe of the cut past the end of the exposed root to the intersection of a straight line projected along the surface of the hillslope. A cross-sectioning technique was then used to determine erosion to the present roadcut surface. A total of 41 exposed root sites were used to estimate erosion on a 1350 m-long section of road. Average erosion was 1·0 and 1·1 cm/year for soil and bedrock respectively. Buttressing by tree roots caused lower erosion rates for soil as compared to bedrock. Both soil and bedrock erosion rates showed statistically significant correlations with the gradients of the original cut slope. The bedrock erosion data provide a reasonable estimate of the disintegration rate of exposed granitic bedrock exhibiting the weathering and fracturing properties common to this area. The road is located in a study watershed where long-term sediment yield data are available. Sediment data from adjacent study watersheds with no roads were compared to sediment data from the roaded watershed to estimate the long-term increase in sediment yield caused by the road. The increase amounts to about 2·4 m³/year. This figure, compared to the average annual on-site road erosion, provides an erosion to sediment delivery ratio of less than 10 per cent. Based on study results, road construction and maintenance practices are suggested for helping reduce roadcut erosion.     

On the relationship of thunderstorm ice hydrometeor characteristics and total lightning measurements

Satellite-borne and ground-based devices for the detection of lightning offer the opportunity to explore relationships–on all significant scales up to global–between lightning frequency, f, and other thundercloud parameters. Calculations predict that f is proportional to the product of the downflux p of solid precipitation and the upward mass flux, I, of ice crystals. This prediction has received support from limited computational studies. The physical reasons for such a relationship are explained in terms of the paramount role of ice in the electrification of thunderstorms. Herein, this prediction is subjected to further, preliminary examination through analysis of lightning and dual-polarimetric radar data collected during the STERAO experiment conducted in Northern Colorado during the summer of 1996. The analysis has yielded some highly provisional support for this flux hypothesis. Computed trends of radar derived hydrometeor fractions of solid precipitation and small ice show correlation to the total lightning frequency and raise the possibility of determining values of p and/or I from lightning measurements.It is shown that the extent to which the observed correlations between f and both solid precipitation and small ice trends are or are not strong can provide an indication as to whether the lightning activity is limited by the available concentrations of precipitating or non-precipitating ice in the upper regions of the charging zone of the thundercloud, where most of the charge transfer occurs. It is demonstrated that the most accurate determinations of precipitation rate p from measurements of lighting frequency f are likely to be for conditions where the field-growth is limited by the availability of graupel pellets. It is shown that the simultaneous time variations of f and solid precipitation trends of the type obtained in the STERAO experiment could enable us to determine the nature of the dominant glaciation process operative in the thunderclouds studied.     

Structural evolution of the contact between two Penninic nappes (Zermatt-Saas zone and Combin zone,Western Alps) and implications for the exhumation mechanism and palaeogeography

The boundary zone between two Penninic nappes, the eclogite-facies to ultrahigh-pressure Zermatt-Saas zone in the footwall and the blueschist-facies Combin zone in the hanging wall, has been interpreted previously as a major normal fault reflecting synorogenic crustal extension. Quartz textures of mylonites from this fault were measured using neutron diffraction. Together with structural field observations, the data allow a refined reconstruction of the kinematic evolution of the Pennine nappes. The main results are: (1) the contact is not a normal fault but a major thrust towards northwest which was only later overprinted by southeast-directed normal faulting; (2) exhumation of the footwall rocks did not occur during crustal extension but during crustal shortening; (3) the Sesia-Dent Blanche nappe system originated from a continental fragment (Cervinia) in the Alpine Tethys ocean, and the Combin zone ophiolites from the ocean basin southeast of Cervinia; (4) out-of-sequence thrusting played a major role in the tectonic evolution of the Penninic nappes. An erratum to this article can be found at     

Late Quaternary paleoenvironments of an ephemeral wetland in North Dakota,USA: relative interactions of ground-water hydrology and climate change

This study of fossils (pollen, plant macrofossils, stomata and fish) and sediments (lithostratigraphy and geochemistry) from the Wendel site in North Dakota, USA, emphasizes the importance of considering ground-water hydrology when deciphering paleoclimate signals from lakes in postglacial landscapes. The Wendel site was a paleolake from about 11,500 ¹⁴C yr BP to 11,100 ¹⁴C yr BP. Afterwards, the lake-level lowered until it became a prairie marsh by 9,300 ¹⁴C yr BP and finally, at 8,500 ¹⁴C yr BP, an ephemeral wetland as it is today. Meanwhile, the vegetation changed from a white spruce parkland (11,500 to 10,500 ¹⁴C yr BP) to deciduous parkland, followed by grassland at 9,300 ¹⁴C yr BP. The pattern and timing of these aquatic and terrestrial changes are similar to coeval kettle lake records from adjacent uplands, providing a regional aridity signal. However, two local sources of ground water were identified from the fossil and geochemical data, which mediated atmospheric inputs to the Wendel basin. First, the paleolake received water from the melting of stagnant ice buried under local till for about 900 years after glacier recession. Later, Holocene droughts probably caused the lower-elevation Wendel site to capture the ground water of up-gradient lakes.     

Geodesic polygons on surfaces of revolution

This paper presents a way for computing geodesic polygons on real surfaces of revolution with partly continuous curvature and gives an application to coordinate transformations in geodesic coordinate systems. The specific formulas for an ellipsoid of revolution are briefly mentioned.     

Die kristallographischen Konstanten Yon Löweit

Zusammenfassung Künstlich hergestellter Löweit kristallisiert trigonal in kleinen Rhomboedern. Die Gitterkonstanten für die hexagonale Zelle sind:a = 18,96 Å,c = 13,47 Å. Die systematischen Auslöschungen führen auf die Raumgruppe R 3 oder R 3. Der Zellinhalt wird diskutiert.     

Kaltzeit-Indikatoren im Unterkambrium SO-Schonens (Schweden)

Zusammenfassung Etwa 1,5 km NW Simrisham wurden an der GrenzflÄche Hardeberga-/Norretorp-Glaukonit-Sandstein (U.-Kambrium) unregelmÄ\ig geformte Erhebungen gefunden, die erosive Bildungen darstellen (SchrÄgschichtung teilweise erhalten) und in die überlagernden Norretorp-Schichten hineinragen. Diese GrenzflÄche weist charakteristische Kriechspuren auf, die im noch lockeren Sediment entstanden sein müssen. Da die Erhebungen andererseits nur im verfestigten Zustand den erosiven KrÄften hÄtten standhalten können, und weder Quarz noch Kalzit als Zement in Frage kommen, wird angenommen, da\ die KontaktflÄche Hardeberga/Norretorp-Sandstein zeitweise gefroren war. Weiterhin wurden Schollen und Gerölle eines Glaukonit-Sandsteines (wohl Norretorp-Sandstein) beobachtet, die vermutlich im gefrorenen Zustand von Norretorp-Schichten eingebettet wurden. Die Gesamtheit der Strukturen (Strömungslineare, laminierte Schichtung usw.), sowie die regionalgeologischen und stratigraphischen ZusammenhÄnge machen es wahrscheinlich, da\ zumindest die basalen Teile der Norretorp-Folge in einem energiereichen Litoralmilieu abgelagert wurden.

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In a Lower Cambrian funnel graben, 1,5 km NW of Simrishamn (S Schweden), irregular miniature sea-stacks were found at the boundary between the Hardeberga and Norretorp Sandstone Formations. Their erosive origin is proven by preserved internal cross-laminations. The same boundary typically contains animal tracks indicating that the surface was temporarily soft. The resistivity of the erosion remnants is explained by cementation. As cement, ice appears to be the only likely alternative. Clasts of a glauconitic sandstone (probably Norretorp Sandstone) found within the Norretorp beds were probably transported in a frozen condition. The structures (parting lineation, planar lamination, etc.) together with the regional and stratigraphic setting make it probable that at least the basal part of the Norretorp Glauconitic Sandstone was deposited in a high-energy litoral environment.

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Résumé A environ 1,5 km au NW de Simrisham (Suède méridionale), on a trouvé, au contact du quartzite de Hardeberga et du grès glauconitique de Norretorp, de petites protubérances irrégulières du premier dans le second et dont la stratification entrecroisée, partiellement conservée, montre qu'elles résultent d'une action érosive. Cette surface de contact montre des traces d'animaux qui indiquent que le sédiment sous-jacent était encore mou. Comme ces protubérances n'ont pu résister aux forces érosives que gráce à la compacité de la roche, et que ni le quartz ni la calcite ne peuvent Être invoqués comme ciment, on admet que la surface de contact a été momentanément gelée. En outre des fragments et galets d'un grès glauconieux (probablement de grès Norretorp) ont été réincorporés à l'état congelé dans les couches de Norretorp. L'ensemble des structures (lignes de courant, stratification laminaire fine, etc.) comme aussi les liaisons géologiques et stratigraphiques à l'échelle de la région, rendent vraisemblable, tout au moins pour les couches inférieures du grès Norretorp, leur dépÔt dans un milieu mouvementé.

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/ Hardeberga/Norretorp, , 1,5 - Simrishamn , — — Norretorp. , . . . , , , , , , . — Norretorp. -, , Norretorp. — , -, - , , - , Norretorp .

     

Zu den Kondensationskernverhältnissen von Wien

Zusammenfassung Nach allgemeinen und quantitativen Angaben über die Ursachen der Zu-und Abnahmen der Kondensationskerndichte wird auf die natürliche und industrielle Kernproduktion verwiesen. Auf Grund einjähriger Morgen- und Mittagsbeobachtungen in Wien mit einem Pollak-Kondensationskernzähler wird besonders die Sedimentation, der Washout- und Rainouteffekt, der Einfluss von Austausch und Windadvektion sowie der Jahres- und Wochengang besprochen.

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Summary General as well as quantitative details of reasons of the variations of the density of condensation nuclei is mentioned. Based on one year's records of observations in the morning and at noon in Vienna, executed by menas of a Pollak-condensation nucleus counter especially the effects of sedimentation, washout, rainout, exchange, wind advection, annual and weekly variation is discussed.