Croissance économique des pays émergents et géographie mondiale des pierres précieuses

L’évolution mondiale des activités extractives est de plus en plus dépendante de la demande des pays émergents. Les conséquences de la croissance de ces pays sur les exploitations de pierres précieuses sont complexes car le marché des gemmes a de nombreuses particularités. La demande est étroitement liée aux matrices socioculturelles de chaque pays. Par ailleurs, l’enrichissement des populations a également un impact sur la production de pierres telles que les saphirs ou les rubis. En effet, ces gemmes sont principalement extraites dans des exploitations informelles et cette activité est de moins en moins attractive pour une population dont le niveau de vie s’élève peu à peu. Dans les vastes gisements sri lankais et birmans, l’épuisement de la ressource est une autre menace. Finalement, si la croissance du marché du diamant est assurée par le Canada, la Russie et l’Australie, pour les autres gemmes, l’Afrique de l’Est est devenue le nouvel « Eldorado ». Dans ces pays, les contextes géologiques, économiques, politiques et sociaux sont très favorables au développement des exploitations artisanales de gemmes.<br>Extraction activities evolution is more and more dependent on the increase of demand in the emerging countries. The consequences of this growth on the gemstone mining activities are complex. The gemstone market is very special and the demand depends on the historic and cultural situation of every country. Moreover, for precious stones like rubby and sapphire, the supply coming from this emerging country is also affected by the social and economic changes. As the small scale mining is widely held in this activity, people that are becoming richer are less interested in that kind of job. In Sri Lanka and Burma, the depletion of many deposits is an other challenge. Finally, if new diamonds deposits of Canada, Russia and Australia are supplying the growth of the diamond market, Est Africa looks like the new « Eldorado » for the other gemstones. Geologic, economic, social and political context of these countries are perfectly adapted for the development of new gemstone small scall mining areas

Estimer les houles cycloniques à partir d’observations météorologiques limitées : exemple de la submersion d’Anaa en 1906 aux Tuamotu (Polynésie française)

Les submersions provoquées par les houles cycloniques sont le principal risque naturel dans les atolls de l’archipel des Tuamotu. L’analyse des cyclones récents par des modèles couplés à haute résolution a amélioré la compréhension de cet aléa. La connaissance des houles extrêmes se confronte néanmoins au problème de la représentativité de l’échantillon en raison de la faible fréquence des cyclones en Polynésie française. Cet article propose une méthode permettant d’estimer la taille de la houle en s’appuyant sur de simples observations des conditions météorologiques au niveau du sol. Cette méthode qui fait aussi appel aux simulations numériques de la houle permet d’améliorer la connaissance de ces risques en étendant l’analyse à des cyclones vieux de plusieurs siècles par le biais des archives. La submersion de l’atoll d’Anaa en 1906 est étudiée à titre d’exemple afin de montrer l’intérêt de cette méthode dans le cadre des études de risque.Hurricane swell submersion is the main natural hazard in the atolls of the Tuamotu archipelago. The analyze of recent hurricanes by high-resolution coupled models has improved the understanding of this hazard. Nevertheless, the knowledge of extreme swell events is faced to representativeness problem of the sample caused by the low frequency of hurricanes in French Polynesia. This paper offer a methodology to estimate the size of hurricane swell by analyzing basic weather observations at sea level. This method that is appealing to swell model simulations as well, give an opportunity to improve the knowledge of these hazards by the extending of the analyze to historic hurricanes (more than one century) through archives. The Anaa submersion in 1906 is examined in detail in order to prove the interest of this method in the scope of risk studies

Estimer les houles cycloniques à partir d’observations météorologiques limitées : exemple de la submersion d’Anaa en 1906 aux Tuamotu (Polynésie française)

Les submersions provoquées par les houles cycloniques sont le principal risque naturel dans les atolls de l’archipel des Tuamotu. L’analyse des cyclones récents par des modèles couplés à haute résolution a amélioré la compréhension de cet aléa. La connaissance des houles extrêmes se confronte néanmoins au problème de la représentativité de l’échantillon en raison de la faible fréquence des cyclones en Polynésie française. Cet article propose une méthode permettant d’estimer la taille de la houle en s’appuyant sur de simples observations des conditions météorologiques au niveau du sol. Cette méthode qui fait aussi appel aux simulations numériques de la houle permet d’améliorer la connaissance de ces risques en étendant l’analyse à des cyclones vieux de plusieurs siècles par le biais des archives. La submersion de l’atoll d’Anaa en 1906 est étudiée à titre d’exemple afin de montrer l’intérêt de cette méthode dans le cadre des études de risque.Hurricane swell submersion is the main natural hazard in the atolls of the Tuamotu archipelago. The analyze of recent hurricanes by high-resolution coupled models has improved the understanding of this hazard. Nevertheless, the knowledge of extreme swell events is faced to representativeness problem of the sample caused by the low frequency of hurricanes in French Polynesia. This paper offer a methodology to estimate the size of hurricane swell by analyzing basic weather observations at sea level. This method that is appealing to swell model simulations as well, give an opportunity to improve the knowledge of these hazards by the extending of the analyze to historic hurricanes (more than one century) through archives. The Anaa submersion in 1906 is examined in detail in order to prove the interest of this method in the scope of risk studies

Formal mining investments and artisanal mining in southern Madagascar: Effects of spontaneous reactions and adjustment policies on poverty alleviation

International audienceThe main political concern in the southern areas of Madagascar is poverty alleviation. To alleviate poverty in the area, the government has chosen to enforce adjustment policies of the World Bank Group. According to the World Bank Group's argument, while artisanal mining is supposed to create significant economic, social and environmental problems, large-scale mining investment results in economic and social prosperity. This paper focuses principally on a re-analysis of the debates regarding the relationship between artisanal and large-scale mining and poverty alleviation in developing countries. Further, the paper offers an alternative viewpoint on these issues based on the example of Madagascar. In the last decade, Madagascar has experienced a significant increase in mining activity. Towards the end of the 90s, informal and artisanal mining emerged as one of the most important economic activities of the area with the development of the Ilakaka frontier. At the same time, foreign investments began to benefit from adjustment policies implemented by the government, and large-scale mining operations also commenced. As the local socio-economic system was deeply affected by these developments, it is wise to monitor the effects of each type of mining operation on poverty alleviation. On the one hand, it appears that governance insufficiency has hampered possibilities for broader economic prosperity through large-scale mining investments. On the other hand, while artisanal mining is frequently condemned by scholars, the negative comments seem to be overly pessimistic, as this activity can be demonstrated to provide considerable economic opportunities for both the native and migrant populations

Atoll islets reshaping processes induced by extreme cyclonic waves and calm weather. Evidence from two centuries of megablocks emergences and coral rubble displacements in Anaa, Rangiroa and Tikehau atolls (western Tuamotu archipelago - French Polynesia)

International audienceUnderstanding the islets morphodynamics of polynesian atolls requires a study of their evolution over several decades. These low-lying islands are exposed to highly variable ocean/weather conditions, especially high energy events. This study is based on a diachronic analysis of aerial photographs, in the field measurements and the U/Th dating of megablocks in three atolls in the western part of the Tuamotu archipelago. It presents an investigation of these dynamics from the 19th century until now. This period makes it possible to record the movements of sediments accumulated during decades of calm weather but also to observe the impact of moderate cyclones such as that of 1983. This article also highlights that exceptional cyclones such as those of 1822 and 1906 can dislocate the coral reef and move up the famous Rangiroa megablock whose volume has been significantly refined by photogrammetry at 369 m3. In Rangiroa and Anaa, we have identified three blocks weighting >500 tons that were put in place by these cyclones