Morphological instabilities during rapid growth of metamorphic garnets

Hydrothermal grossular-andradite garnets from contact aureoles in the Oslo region show morphological transitions from planar via cellular to hopper-like structures. Dodecahedral surfaces {110} dominate during the planar growth stage, whereas the stable crystal faces, developed during the cellular and hopper stages also includes the ikositetrahedron {211} and possibly the hexoctahedron {321}. Faceted cells develope when initially ‘wavy’ perturbations on the dodecahedral surfaces become tangential to lower-index planar surfaces. Inclusion patterns and morphologies of almandinerich garnets from Magerøy (northernmost Norway) that formed during a period of rapid heating, suggest an early stage of cellular growth followed by planar growth. The morphological transitions suggest that the hydrothermal garnets experienced an increase in the overstepping of the garnet precipitation reaction at some stage during their growth whereas the opposite was the case during growth of the Magerøy garnets. The present observations put constraints on the garnet growth rates and emphasize the importance of growth kinetics during metamorphic processes.     

Production of atmospheric condensation nuclei by solar radiation

Summary Air with a very low count of atmospheric condensation nuclei was irradiated by direct sunlight through an uviol glass window, or through ordinary glass or in a polyethylene balloon. The nucleus count rises immediately and reaches very high values.

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Zusammenfassung Luft mit sehr niedriger Zahl von atmosphärischen Kondensations-Kernen wurde mit direktem Sonnenlicht bestrahlt, entweder durch ein UV Glas oder durch gewöhnliches Glas oder durch einen Polyethylen-Ballon. Die Zahl der atmosphärischen Kondensations-Kerne steigt sogleich und erreicht sehr hohe Werte.

     

Directivity in the stream-plasma interaction

Center-to-limb variations indicate that a type III burst is likely to be emitted in a radial direction while a type IIIb emission is more perpendicular to the stream.     

Analytical transmission electron microscopy of oscillatory zoned grandite garnets

Oscillatory zoned grandite garnets from skarns of the Oslo rift region (southern Norway) have been studied using analytical transmission electron microscopy (ATEM). Our results show lamellae with a width varying from about 10 nm to more than 500 nm in both periodic and non-periodic sequences, which represent oscillatory zoning at a very fine scale. The compositions of adjacent lamellae alternate bimodally from X_and=0.55-0.75 to X_and=0.95-1.0. High resolution (HRTEM) images show that the compositional interfaces are sharp and coherent. Oscillatory zoning at the nm-scale puts constrains on the origin of oscillatory zoning in grandites and underlines the dynamic nature of the crystal growth process. The influence of growth rate is discussed against the background of local growth dynamics and external forcing at different length scales. This study emphasises the importance of adequate spatial resolution in analysing chemical variations in grandite garnets and shows that commonly applied methods (e.g. optical microscopy, backscattered electron imaging and electron or ion microprobe) are not sufficient to detect 'real' zonation patterns. Finally, proposed hypotheses on the origin of birefringence of grandite garnets with intermediate compositions are reviewed and discussed on the basis of the observed microstructure.     

Application of infrared thermography for mapping open fractures in deep-seated rockslides and unstable cliffs

We present a new approach for mapping open cracks and tension fractures within rock slope instabilities and rock cliffs, which resides in high-resolution ground-based and airborne infrared thermography (IRT). The method is restricted to cold seasons, and its utility is demonstrated through three examples from the Flysch Belt of the Outer West Carpathians (rockslides at Kopce Hill and Mt. Kněhyně) and from the Northern Calcareous Alps (deep-seated gravitational slope deformations in Gschliefgraben/Mt. Traunstein). The approach is based on a contrast between temperatures deep within the rock mass, which at a depth of few meters represent local mean annual values, and winter-time temperatures of the ground surface. In winter, warmer, buoyant air from depth rises to the ground surface through open cracks and joints, and the temperature contrast can be detected by IRT. Our test survey was conducted in the beginning of February 2012, in order to achieve the best contrast between temperatures around open tension cracks and the adjacent ground. For temperature sensing, we used a FLIR B360 thermal camera; for airborne surveys in the ambient air, temperatures at the time of our surveys ranged from approximately ?19 to ?7 °C. IRT results conclusively revealed the presence of open cracks, loosened rock zones, and pseudo-karst caves over a distance sometimes greater than 1 km. The IRT approach proved useful for rapidly assessing the distribution of open cracks and tension fractures, key information required for assessing rockfall and rockslide hazard.     

Estimation of a non-stationary prior covariance from seismic data

Non-stationarity in statistical properties of the subsurface is often ignored. In a classical linear Bayesian inversion setting of seismic data, the prior distribution of physical parameters is often assumed to be stationary. Here we propose a new method of handling non-stationarity in the variance of physical parameters in seismic data. We propose to infer the model variance prior to inversion using maximum likelihood estimators in a sliding window approach. A traditional, and a localized shrinkage estimator is defined for inferring the prior model variance. The estimators are assessed in a synthetic base case with heterogeneous variance of the acoustic impedance in a zero-offset seismic cross section. Subsequently, this data is inverted for acoustic impedance using a non-stationary model set up with the inferred variances. Results indicate that prediction as well as posterior resolution is greatly improved using the non-stationary model compared with a common prior model with stationary variance. The localized shrinkage predictor is shown to be slightly more robust than the traditional estimator in terms of amplitude differences in the variance of acoustic impedance and size of local neighbourhood. Finally, we apply the methodology to a real data set from the North Sea basin. Inversion results show a more realistic posterior model than using a conventional approach with stationary variance.