Halogen content of some African primary carbonatites

Colorimetric analyses have been made for F, Cl and I in a suite of African carbonatites specially selected for their freshness. F and Cl vary widely both in absolute and relative amounts between intrusions, but F/Cl ratios are usually consistent in samples from the same intrusion. Although samples from both the 2 b.y. Phalaborwa complex and the modern Oldoinyo Lengai lavas have low F/Cl values, there is considerable variation during geological time. Iodine (up to 1.8 ppm) has been found in the carbonatites of Phalaborwa, Sukulu and Oldoinyo Lengai; the only common factor seems to be the high sulphur content of the carbonatites at these localities.     

Floorspace to worker ratios in shopping centres: A note

The characteristics of employment within the retailing sector are still poorly understood. This short paper expands on a previously presented study of Canberra (Geoforum10, 407–425) by reporting on the systematic variation between the ratio of floorspace to employees and type of shopping centre, and the different relationships between floorspace per worker and size of store by type of shopping centre. The planning implications in terms of employment provision are briefly discussed.     

Activity of the carbonatite volcano Oldoinyo Lengai, 1966

From 1960 to August, 1966, the activity of Oldoinyo Lengai took the form of quiet extrusion of carbonatite lava. In August, 1966, the style of activity changed abruptly and violent ash eruptions took place. The activity varied from minor emissions of ash to major Plinian and Vulcanian type eruptions. A new ash-cone built up within the crater and ash was widely distributed on the slopes of the volcano and over the surrounding countryside.The ash consists of sodium carbonate mixed with crystals of nepheline, pyroxene, wollastonite, apatite, melanite and pyrite. Also blocks of ijolite and melteigite were ejected during the activity.

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Zusammenfassung Von 1960 bis zum August 1966 bestand die Tätigkeit des Vulkans Oldoinyo Lengai/Ostafrika in ruhigen Lava-Extrusionen. Im August 1966 änderte sich plötzlich die Art seiner Tätigkeit, und heftige Aschenbrüche fanden statt. Diese Tätigkeit variierte von kleineren Ascheneruptionen bis zu größeren Ausbrüchen plinianischen und vulkanischen Typs. Ein neuer Aschenkegel entstand in dem aktiven Krater, und Asche wurde weithin über die Abhänge des Vulkans und über die Umgebung verteilt.Die Asche besteht aus Natrium-Karbonatit mit einer Beimischung von Kristallen von Nephelin, Pyroxen, Wollastonit, Apatit, Melanit und Pyrit. Während des Ausbruchs wurden auch Ijolith- und Melteigitblöcke ausgeworfen.

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Résumé De 1960 jusqu'en août, 1966, l'activité du volcan Oldoinyo Lengai consistait en coulées tranquilles de lave carbonatitique. En août, 1966, le genre d'activité changea abruptement et de violentes éruptions de cendres se produisirent. L'activité consistait tantôt en de petites émissions de cendres, tantôt en éruptions majeures du genre Plinien et Vulcanien. Un cône neuf de cendres s'amoncelait dans le cratère actif, et les cendres se dispersaient sur le pays environnant.Les cendres se composaient de carbonatite alcaline avec des cristaux de nephéline, pyroxène, wollastonite, melanite et de pyrite. D'ailleurs des blocs d'ijolite et de melteigite furent projetés hors du cratère pendant l'activité.

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Oldoinyo Lengai ( ). 1960 1966 . , . Na- , , , , .

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Dedicated to Professor Dr. A.Rittmann on the occasion of his 75. birthday     

Ball lightning as a radiation bubble

Summary A model for ball lightning is presented and its properties discussed. The model is that of a microwave radiation field contained within a plasma dielectric sphere, resonant at a frequency much greater than the electron-molecule collision frequency. Calculations are made of the energy stored in the microwave field, the electron temperature, the rate of energy loss due to ionization, and the effects of recombination. It is concluded (a) that a self-consistent set of conditions can be obtained only when the neutral density within the sphere is much lower than atmospheric, and (b) that the microwave field strength required is of the order of 10⁹V/m. Under these conditions the radiation pressure becomes comparable to that of the atmosphere; the second case investigated is when these two become equal. It is then found that this radiation bubble appears to satisfy the requirements imposed on energy storage and dissipation, recombination and resonant frequency. The electron density in such a bubble is found to be typically 10¹¹ cm^–3 and the stored energy typically 10³ Joules. A discussion is given of some of the problems associated with the model-formation, stability, neutral number density, and the problem of hydrostatic equilibrium.     

Hazard transformation and hazard management issues in the London megacity

Megacities are likely to present the greatest future challenges for hazard management. In them increasingly complex societies are continually modifying responses to dynamic sets of external risks. Although most have proven resilient to past disasters, new types of threat are emerging. London — which is both the world's oldest megacity and one of its most resilient — has long experience of the transformation of hazards in time and space. Although not as hazard-prone as some megacities, this one is increasingly exposed to a wide range of interactive hazards. Here trends of flooding, air pollution and terrorism are discussed together with policy responses. London demonstrates that robust action can be successful in reducing high-intensity hazards but it also shows that contemporary management is characterised by top-down technological fixes whose long-term effectiveness is questionable. In general, anticipatory responses have been limited and present-day London has not capitalised on its rich legacy of successful experience in coping with hazard.     

Sustaining agricultural production and food security in Southern Africa: an improved role for climate prediction?

Livelihoods and household food security in the Southern African region can be extremely vulnerable to the negative effects of climate stress as shown by the 2002–2004 ‘complex emergency.’ Climate prediction may prove a valuable resource in mitigating these effects. If climate prediction is applied successfully, it may be able to help guide responses in populations at risk to reduce vulnerability to climate stress. The study presented here seeks to understand what would constitute an improved role for climate prediction in contributing to sustaining agricultural production and food security in Southern Africa. Investigation undertaken during the 2002/2003 rainy season under regional conditions of elevated disaster risk shows, however, that a number of weaknesses and gaps persistently characterize climate information systems in the Southern African region, and constrain such systems’ ability to benefit key sectors, particularly agriculture. The stakeholder identification of such gaps forms the basis for distilling concrete recommendations to improve process and organizational efficiency. Such recommendations, while developmental, should better enable institutions and stakeholders involved in climate prediction to fulfill their potential in supporting development of successful adaptation strategies in populations and sectors at risk.