A study of the gully phenomenon in Gombe Town,Bauchi State: Bedrock geology and environmental implications

In Gombe, Bauchi State, Nigeria, gullies are sculptured in the Upper Cretaceous Pindiga Formation and Gombe Sandstones. The former is a sequence of marine shales with limestone interbeds, the later is a sequence of sandstone, siltstone, and shales. Both formations have ironstone cappings. The degree of gully development, the gravity of attendant soil wastage, and environmental hazards are all related to the rock types in which the gully have formed. Hence, the most grievous situations are posed by gullies in the shale/clay member of the Gombe Sandstone and in the shale/clay/limestone units of the Pindiga Formation. An undercut and collapse model is put forward to explain gully initiation and propagation in Gombe.     

Natural boehmite single crystals from Ceylon

Single crystals of boehmite, up to 0.1 mm in size, were found in open cavities inside a corundum crystal from the Ratnapura area gem gravels in Ceylon. The unit cell parameters are (X-ray powder pattern): a ₀=3.695 Å b ₀=12.212 Å, c ₀=2.867 Å. The crystallographic orientation is based on X-ray single-crystal precession photographs. The crystals show the faces (it010), (001), (101), and (221). Systematic extinctions agree with the space group Amam. Optical orientation: a, b, c. Refractive indices are given. The mineral is optically positive with a large optic axial angle.     

The morphological characteristics of gully systems and watersheds in Dry-Hot Valley,SW China

Gully systems and watersheds are geomorphic units with clear boundaries that are relatively independent of basin landscapes and play an important role in natural geography. In order to explore the morphological characteristics of gully systems and watersheds in the Dry-Hot Valley [South West (SW) China], gullies are interpreted from online Google images with high resolution and watersheds are extracted from digital elevation model at a scale of 1:50,000. The results show that: (1) There are 17,382 gullies (with a total area of 1141.66 km²) and 42 watersheds in the study area. (2) The average gully density of the study area (D) is 4.29 km/km², gully frequency (F) is 14.39 gullies/km², the branching ratio (B) is 5.13, the length ratio (L) is 3.12, and the coefficient of the main and tributary gullies (M) is 0.06. The degree of gully erosion is strong to extremely strong, the main development intensity of gully erosion ranges from intense to moderate, and the type of gully system is tributary. (3) The watershed areas (A) are between 0.39 and 96.43 km², the relief ratio (R) is from 0.10 to 0.19, the circularity ratio (C) is from 0.30 to 0.83, the texture ratio (T) is from 0.82 to 39.35, and the dominant geomorphological texture type is fine. (4) There is a quantitative relationship between F and D:F?=?0.624D² (R?=0.84) and T is closely related to D, F, M (R²?>?0.7). A, R and C are related to M (R²?>?0.5). The development of gully systems is the result of coupling effects between multiple factors. In this area, the degree of erosion and the condition of the main and tributary gullies can be controlled by the degree of topographic breakage in the watershed, which provides some theoretical basis for the evaluation of gully erosion by the latter. In addition, the scale, relief, and shape have a significant impact on the locations of the main and tributary gullies. For tributary gullies, attention should be paid to the interception and control of runoff and sediment in the small confluence branches in order to prevent gully expansion and head advance. These features can inform the development of targeted measures for the control of soil erosion.     

Strike stabilizing pillars as a regional support strategy for ultra-deep gold mines

Strike stabilizing pillars are included in the mine layout of a number of deep South African gold mines as a means of providing regional support with the principal aim of controlling rockbursts. Large seismic events associated with stabilizing pillars can cause extensive damage to working areas. Mining-induced seismicity recorded at Western Deep Levels Limited has been analysed in an attempt to improve the design of stabilizing pillars, and thereby reduce their associated seismic hazard. This work revealed that the vast majority of stabilizing pillars, regardless of their dimensions and those of their adjacent stopes, will, at some time, give rise to seismic events of magnitude, M2. Contrary to expectations, this work strongly indicates that the rock mass in the near vicinity of the mined out areas does not behave in an elastic manner. Consequently, the currently employed design methodologies, based on elastic principles, should not provide the only criteria when designing strike stabilizing pillars.     

Prehistoric and recent mass movements of the World Cultural Heritage Site Hallstatt, Austria

Hallstatt Village, located in the Austrian Alps, is designated by the United Nations Educational, Scientific and Cultural Organization as part of the World Cultural Heritage Site Hallstatt–Dachstein. This region is recognized for its salt deposits that have been exploited since the Neolithic period. In former times, these salt deposits were very rare and precious. Due to unfortunate bedding conditions, mass movements have been frequent in the past and continue to affect the site today. These active and inactive mass movements were mapped geotechnically to a scale of 1:5,000 and the mineralogical and mechanical properties of the main instable soft rocks were investigated. Rock spreads, rock slides, rock falls, rock topples, earth flows and earth and debris slides are the primary types of mass movements recorded. They are most frequently observed in areas affected by mining, though they may also occur in areas where no anthropogenic influence is recognized. Evidence exists in the archaeological record that indicates prehistoric mining activities were also seriously affected by the impact of mass movements.     

Karsts polyphasés, faciès marins et continentaux dans le Paléocène de la partie orientale des Pyrénées fran?aises

In the Eastern part of French Pyrenees, the Cucugnan area (Southern Corbières) corresponded during the early/Mid-Paleocene (Danian/Selandian) to a narrow transitional zone between the sea to the South (Pyrenean Paleocene Trough) and the continent (fluvio-palustrine and lacustrine Vitrollian deposits) to the North. To the South, in the North-Pyrenean Zone, the polygenic marine breccias and the associated Dano-Selandian Globigerinid-bearing hemipelagites have been preserved within successive paleokarsts superimposed onto the carbonate substratum (ante-Albian). Four paleosurfaces are recognized, principally filled by marine internal sediments with proximal and distal facies. To the North, in the Sub-Pyrenean Zone, a continental foreland basin is characterized by four formations of variegated Microcodium-bearing marls and channelized conglomerates, separated by erosional paleosurfaces underlining well-marked unconformities. An event correlation (chronodiagrams) between the marine realm to the South and the continental realm to the North is proposed, using the successive paleosurfaces and the lithological sequences (same number within the two realms). Our paleogeographic reconstruction shows, to the North, the Lake of Cucugnan and, to the South, a calcareous mountainous zone broken by the juxtaposition of deep paleocanyons (eroded in a continental context) later converted into rias submitted to marine oscillations. Several palinspastic transects are reconstructed: they show the polyphase control of the Frontal North-Pyrenean Overthrust on the Paleocene sedimentation and the importance of the successive intra-Vitrollian compressions/ transpressions (phase fini-crétacée auct.) inducing, within the two juxtaposed realms, emersions, erosions and karstic features which give a very contrasted paleogeography during a period characterized by plate convergence and creation of steep topographies.Manuscrit reçu le 25 septembre 2003 Révision acceptée le 4 mai 2004     

Fracture mechanisms of offset rock joints-A laboratory investigation

To study the failure mechanisms of joints and rock bridges in jointed rock masses a series of uniaxial compression tests were performed on specimens made of rock-like material. Specimens of size 63.5cm × 27.9cm × 20.3cm, made of 72% silica sand, 16% cement (Type I) and 12% water by weight were tested. The joint inclination angle was maintained at 45°, while the offset angle i.e. angle between the plane of the joint and the line that connects the two inner tips of the joints, was changed from 0°–120° with an increment of 15°. The tests were performed using a 2000kN universal compression machine and a HP data acquisition system. In each sample, five LVDTs were fixed to measure the displacements along and across both the bridge and the joint segment, and the total displacement along the total length of the sample. The failure mechanism was monitored by visual inspection and a magnifier to detect cracks initiation. For each test the failure surfaces were investigated to determine the characteristics of each surface. In all of the tested samples curvilinear cracks called wing cracks initiated at the joints tips due to high tensile stresses concentration. These wing cracks were directed along the direction of the uniaxial load. The coalescence mechanism of two cracks was investigated. Results showed that open cracks could coalesce by shear failure or tensile failure. The coalescence path was found to be mainly dependent on the inclination of the rock bridge between the cracks.     

A review of lognormal estimators forin situ reserves

The term lognormal kriging does not correspond to a single well defined estimator. In fact, several types of lognormal estimators forin situ reserves are available, and this may cause confusion. These estimators are based on different assumptions—that is, different models. This paper presents a review of these estimators.     

Estimating quartz fabrics from piezoelectric measurements

An aggregate of piezoelectric minerals may itself be piezoelectric if the minerals are suitably aligned. Thus quartz-bearing rocks may be piezoelectric, since quartz is one such mineral. It has been shown that some rocks do possess this effect, termed a piezoelectric fabric (Bishop, 1981). The type of piezoelectric fabric may be determined by matching experimental data to theoretical models of piezoelectric fabrics. These theoretical models of pure quartz aggregates are derived by considering the symmetry of the preferred crystallographic directions of the aggregate grains. From the symmetry, the piezoelectric matrix of the model may be determined. The best-fitting model and the orientation of its fabric is obtained by equating the experimental data to each model in turn. For each model, the best fitting fabric orientation is determined by using an inversion routine. If the experimental data are due to a piezoelectric fabric and not to some random or nonpolar distribution of grains, the fabric type (c-axis point maximum or large-circle girdle) and its orientation with respect to the specimen may be determined. The positions and polarities of the quartz a-axes are also specified. A statistical examination of results from a quartz-mylonite shows that the problem of piezoelectric model fitting is well posed, in that the Eulerian angles that specify the fabric orientation are fairly independent important parameters and a sufficiently close fit of the model to the data can be obtained to determine the fabric.     

The analysis of zoning in magmatic crystals with emphasis on olivine

Many of the observed features of zoning in magmatic phenocrysts may be due to the orientation of the section rather than inherent properties of the crystals. An ideal section for the studying of zoning in magmatic crystals has two characteristics: it goes through the center of the crystal, and is perpendicular to one or more crystal faces. Using a model zoned olivine crystal, it is possible to construct accurate zoning profiles for different types of section (centered, symmetrical and skewed). The probability of obtaining a random section which passes within x% of the center of a crystal is shown to be P=0.0x, while the probability that a random section will be within A degrees of perpendicular to a given plane is P=sin(A). A systematic approach to the study of zoned crystals is outlined. In particular, it is suggested that composition be plotted against distance cubed, in order to correct for the volume versus size problem. A method of determining if a given section goes through (or near) the center of a zoned crystal is also presented. The reasoning in this work applies to other types of magmatic crystals such as pyroxenes and plagioclase.     

Modal and vectorial analysis for determination of stress axes associated with fault slip data

Based on Anderson's faulting theory, for a given set of fault slip data including the sense of slip on faults and fault planes, this paper provides two possible methods to reconstruct the principal stress axes using vectorial and modal analysis procedure. The vectorial analysis consists of computing eigenvectors of the orientation matrices defined by axes P, B, and T (P, B, and T being geometrical axes parallel to axes ₁, ₂, ₃ associated with a single striated fault) which are determined geometrically knowing the slip vector S, the normal to fault plane N, and the dihedral angle 2. A parameter R, related to the maximum eigenvalue of the orientation matrix and the size of data sample, is shown to be a good test value for the homogeneity of the data. A process of refinement of this parameter enables bad data (representing faults generated under different tectonic events) to be ignored in the final computation of the principal stress axes; results are thus significantly improved and the vectorial analysis procedure enables the orientation of stress to be numerically determined. On defining probability density regions around each P, B, and T axes that incorporate the variation of fault geometry, the modal analysis is carried out in two density functions established by a convolution process to locate modes which represent optimal locations of the principal stress axes in spherical space. Splitting of heterogeneous data samples into homogeneous subsets is achieved by a dynamical cluster procedure which enables the principal stress axes associated with each subset to be determined separately.     

Utilization of data bank on grid square basis for regional planning

This paper deals with results of case studies using actual magnetic tape records of Statistics on Grid Square Basis and Digital National Land Information which have been compiled since 1965 by governmental agencies on the same grid square basis from census and map reading covering the whole country. The number of items on the records has been increasing, including land information and socio-economic statistics which seem to be useful for land development/conservation planning and regional planning. However, in reality a majority of local governments have not used to date these records enough. In this study the combination analysis of two or more items is made in order to make more effective use of the records for these plannings. The number of grid squares under fixed conditions are calculated and the distribution maps are drawn by means of line printer or X-Y plotter. The themes are as follows: 1. Population distribution and population growth and land use type by landform classification, 2. Proportion of built-up area in city planning area, 3. Selection of possible space for housing development, 4. Division of a given area based on natural conditions for daily life into three areas, namely suitable areas, possible but rather difficult areas, and unsuitable areas. 5. Selection of suitable areas for sightseeing and recreation. The items used for combination analysis are 1970 and 1975 Population Census, ground elevation, angle of inclination, value of relief, landform classification, surface geology classification, soil classification, land use classification, and city planning area. The data of land value and distance from nearest station are produced by map reading for the test area in this study. From these combinations an objective and detailed distribution can be determined. Finally, several examples of the studies are shown.     

Seismic history and consistent seismicity: Evidence from southern Italy

In this paper a method is proposed to evaluate the seismicity level of an area in a given historical period, based on records of seismic events, source characteristics and intensity attenuation with distance. Also considered is the seismic activity recorded in southern Italy during the 10th and 11th centuries, seismic records being obtained from all available sources. To determine the level of seismicity, a key role is played by source characteristics, i.e. recording modalities and activity periods of recording centers. In addition, models of intensity attenuation with distance allow the assessment of the size of the area under investigation. This paper identifies the areas, in the 10th and 11th centuries, where major earthquakes (M 6.5) did not occur during periods of silence of sources, as well as those where such events cannot be excluded. For each area, different levels of probability were determined by applying the Cox linear logistic model to historical seismic data. The completeness analysis, in terms of area and time-span coverage, is a valuable tool to assess seismicity in seismogenetic areas. The reproducibility of the model for lower magnitude earthquakes (M < 6.5) is reliable.     

Determination and interpretation of preferred orientation with texture goniometry: An application of indicators to maximum entropy pole- to orientation-density inversion

The probability density function of orientations of crystals generally cannot be measured directly without destruction of the specimen. Therefore it is usual practice to sample pole density functions of several crystal forms in diffraction experiments with a texture goniometer. Determining a reasonable orientation density function from experimental pole density functions is then the crucial prerequisite of quantitative texture analysis. This mathematical problem may be addressed as a tomographic inversion problem specified by the crystal and statistical specimen symmetries and the properties of the diffraction experiment. Its solution with maximum entropy preferred orientation portion and maximum uniform portion is proposed because it yields the most conservative orientation density function with systematically reduced correlation effects, thus avoiding artificial texture ghost≓ components caused by the specific properties of the diffraction experiment.     

A method for assessment of excavation damaged zone (EDZ) of a rock mass and its application to a dam foundation case

Excavation of slope is an unloading process, and also an energy releasing process when the stress in the rock mass is unloaded, leading to the rebounding deformation towards the free face. And then a zone, namely excavation damaged zone (EDZ), will be formed near the excavation boundary, where the rock is damaged or disturbed and its physical, mechanical and hydraulic properties are greatly changed. This paper is to put forward a new method to quantify the extent and damage degree of the EDZ according to the unloading strain energy which is released in the process of excavation. A simple relationship between unloading strain ε and accumulative opening displacement T of cracks, , is proposed to describe the damage degree of rock mass in the EDZ, where h is the depth variable in normal direction of the open cracks.This method is used to assess the EDZ of the dam foundation at Xiaowan hydropower station in southwestern China by the accumulative opening displacement curves of cracks along boreholes based on boreholes camera photos. We find that the EDZ can be naturally divided into two sub-zones, i.e. the excavation heavily disturbed sub-zone (EHDZ) and excavation slightly disturbed sub-zone (ESDZ), according to the variation of unloading strain ε. Two inflexions of the accumulative opening displacement curve indicate the lower limits of EHDZ and ESDZ respectively.     

Dreiaxiale verformungen an Solnhofener Kalkstein im Temperaturbereich von 20–650° C. Röntgenographische Gefügeuntersuchungen mit dem Texturgoniometer

Axial-symmetric and real triaxial deformation tests on Solnhofen limestones were made in the range of 20 to 650° C. Stress, strain and time observations as functions of temperature and the ratios of the external stresses are plotted as stress-strain and strain-time curves. Mechanical twinning on e (01¯12) and syntectonic recrystallization (at temperatures above 500° C) is assumed to be the dominant flow mechanism. On samples of high permanent strain the textural changes and development of preferred orientations were investigated by means of the X-ray diffractometer. In all tests the symmetry of the polefigures is exactly identical with the symmetry of the external stress-field.In tests with ₁>₂=₃ the poles of the planes investigated (10¯11; 10¯12; 11¯20) occupy girdles about the unique principle compressive axis. When all principle stresses are different (₁>₂>₃) the poles of the planes investigated tend to maxima (in the case of plane strain) ore to girdle-occupations about the principle axis of maximum extension. The deduced c-diagrams show a fairly similar tendency of the spacial orientations.The pole figures (as well as the calculated orientation of the c-axis) must be explained by the superposition of reflected intensities on planes in twinned and untwinned grains. In every diagram partial occupations—possibly representing the orientations of twinned grains-are in fairly good agreement with the orientation predicted by the theory of Brace-MacDonald for the stable orientation of anisotropic minerals in a non-hydrostatic stress-field.

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Herrn Prof. Dr. F. Karl danke ich sehr herzlich für zahlreiche Diskussionen sowie für die kritische Durchsicht des Manuskripts. Mein Dank gilt auch der Deutschen Forschungsgemeinschaft, welche die Untersuchung durch eine Sachbeihilfe unterstützte.     

Radon in soil anomaly observed at Los Azufres geothermal field,Michoacan: a possible precursor of the 1985 Mexico earthquake (Ms = 8.1)

A radon anomaly in a nuclear track detector placed on a fault was detected prior to the destructive (Ms = 8.1) Mexican earthquake of 19 September 1985. The fault is a structural feature of the geothermal field Los Azufres, 260 km NE of the epicentral area. Since no other phenomenon can be found as a possible cause for the radon anomaly, it is proposed that preseismic regional stress perturbations may produce changes in the fluid transport patterns at the fault, suggesting that radon measurements in similar conditions could provide a good precursor in high seismic risk areas.     

Stratigraphie und Tektonik der Schuppenzone Elbas

Zusammenfassung Die Serien der Schuppenzone Elbas zeigen eine durchlaufende stratigraphische Folge vom Paläozoikum bis ins Tertiär. Ein intensiver ostvergenter Falten- und Schuppenbau führt zu einer mehrmaligen Wiederholung bestimmter Gesteinsserien. Es sind 5 größere Schuppen oder Schuppenzonen auszuscheiden, die dem im Süden sich heraushebenden Autochthon überschoben sind. Die syntektonisch aufgedrungenen Granite haben das tektonische Geschehen beeinflußt. Das benachbarte Festland und das übrige toskanische Archipel zeigen denselben Baustil wie die Insel.

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Imbricated zones of the Isle of Elba display a continuous sequence from Paleozoic to Tertiary beds in several repetitions. Five larger thrust-zones override an autochthonous Eastern unit which appears (tilted up) in the South. Syntectonic granites. The tectonic style corresponds to the neighbouring continental situation.

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Résumé Les séries de la zone des écailles de l'île d'Elbe montrent une succession stratigraphique continue allant du Paléozoïque jusqu'au Tertiaire. Une structure en écailles et en plis fortement déversés vers l'est amène de nombreuses répétitions de certaines séries de roches. On peut distinguer 5 écailles et zones d'écaillés majeures qui sont refoulées sur l'autochtone affleurant au Sud. Les granites, mis en place syntectoniquement, ont influencé la tectonique. Le continent avoisinant et le reste de l'archipel toscan montrent le même style structural que les îles.

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Mean and turbulent velocity measurements of supersonic mixing layers

The behavior of supersonic mixing layers under three conditions has been examined by schlieren photography and laser Doppler velocimetry. In the schlieren photographs, some largescale, repetitive patterns were observed within the mixing layer; however, these structures do not appear to dominate the mixing layer character under the present flow conditions. It was found that higher levels of secondary freestream turbulence did not increase the peak turbulence intensity observed within the mixing layer, but slightly increased the growth rate. Higher levels of freestream turbulence also reduced the axial distance required for development of the mean velocity. At higher convective Mach numbers, the mixing layer growth rate was found to be smaller than that of an incompressible mixing layer at the same velocity and freestream density ratio. The increase in convective Mach number also caused a decrease in the turbulence intensity ( _u /U).List of Symbols a speed of sound - b total mixing layer thickness betweenU ₁ – 0.1U andU ₂ + 0.1U - f normalized third moment ofu-velocity,f u ³/(U)³ - g normalized triple product ofu ² v,g u ² v/(U)³ - h normalized triple product ofu v ², h uv' ²/(U)³ - l _u axial distance for similarity in the mean velocity - l _u axial distance for similarity in the turbulence intensity - M Mach number - M _c convective Mach number (for ₁=₂),M _c (U ₁–U ₂)/(a ₁+a ₂) - P static pressure - r freestream velocity ratio,rU ₂/U ₁ - Re unit Reynolds number,Re U/ - s freestream density ratio,s ₂/ ₁ - T _t total temperature - u instantaneous streamwise velocity - u deviation ofu-velocity,u u–U - U local mean streamwise velocity - U ₁ primary freestream velocity - U ₂ secondary freestream velocity - U average of freestream velocities, ¯U (U ₁ +U ₂)/2 - U freestream velocity difference,U U ₁ –U ₂ - v instantaneous transverse velocity - v deviation ofv-velocity,v v – V - V local mean transverse velocity - x streamwise coordinate - y transverse coordinate - y ₀ transverse location of the mixing layer centerline - ensemble average - ratio of specific heats - boundary layer thickness (y-location at 99.5% of free-stream velocity) - similarity coordinate, (y –y ₀)/b - compressible boundary layer momentum thickness - viscosity - density - standard deviation - dimensionless velocity, (U –U ₂)/U - 1 primary stream - 2 secondary stream A version of this paper was presented at the 11th Symposium on Turbulence, October 17–19, 1988, University of Missouri-Rolla     

Cell parameters of thermally treated anorthite. Al,Si configurations in the average structures of the high temperature calcic plagioclases

Thermal treatments of anorthite carried out at up to 1,547° C show that the unit cell parameter changes as a function of the treatment temperature. The best fit curve found by non-linear least squares analysis is: =91.419-(0.327·10^-6)T ²+(0.199·10^-12)T ⁴-(0.391·10)T ⁶. The results obtained support significant Al,Si disorder (Al0.10, where Al=t ₁(0)-1/3 [t ₁(m)+t ₂(0)+t ₂(m)], Ribbe 1975), in anorthite equilibrated near the melting point and confirm a high temperature series differentiated from the low temperature series for calcic plagioclases in the An₈₅–An₁₀₀ range also. In the plot vs. An-content the high and low temperature curves intersect at An₈₅ composition and progressively diverge in the An₈₅–An₁₀₀ range. The trends of the high and low temperature curves in this range are interpretable on the basis of the degree of Al, Si order in the average structures of calcic plagioclases.