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In 1879, the RGS started courses in practical surveying based on the methods used by navigators. Subsequently, RGS courses, increasingly under the influence of former members of the Survey of India, changed in character. At the same time as the nature of appropriate surveying was being negotiated within the RGS, the debate over the academic nature of geography also took shape. The development of the 'new' geography reflected the conflicts within the RGS Council over the meaning of scientific geography. 相似文献
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Peter Griggs 《The Australian geographer》2002,33(1):43-61
The growing of tobacco was one of the most tightly regulated industries in Australia, until deregulation in 1995. Commonwealth regulations controlled the area cultivated with tobacco, the number of growers (i.e. quota holders) and marketing arrangements for tobacco leaf. This paper begins by outlining the nature and historical development of controls in the tobacco-growing industry, and discusses how the Commonwealth government removed the industry's regulatory and protective framework in 1995. The third part of the paper examines how deregulation has impacted upon the Mareeba-Dimbulah Irrigation Area, Far North Queensland, where small farmers produced 60 per cent of Australia's tobacco in 1995. The discussion will show that the agricultural landscape once dominated by tobacco has been transformed, as local farmers abandoned growing tobacco in favour of sugar cane, avocadoes, mangoes, macadamia nuts and other small vegetable crops (e.g. navy beans, pumpkins). Tobacco, once promoted by the Queensland government as a crop to facilitate closer settlement in the Mareeba-Dimbulah Irrigation Area, will have almost vanished from the landscape by 2002. 相似文献
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Distribution and morphology of sinkholes triggered by flooding following Tropical Storm Alberto at Albany, Georgia, USA 总被引:1,自引:0,他引:1
Flooding of the Flint River in July 1994 triggered the collapse of at least 312 sinkholes in the karstic Dougherty Plain at Albany, Georgia. We examined the distribution and morphology of these new sinkholes to evaluate the mode of formation, to characterize early stages of the evolution of sinkhole form, and to estimate the lowering of the surface associated with the development of new sinkholes.Eighty-eight percent of sinkholes occur inside the limits of flooding, especially in areas of sandy overburden, and they often follow joint-controlled linear trends. Sinkhole dimensions are log-normally distributed with median values of circumference = 5.7 m, length = 1.8 m, width = 1.6 m, and depth = 0.7 m; asymmetry (L:W) = 1.2. Cross-sectional forms range from narrow cylinders to large bowls, with many sinkholes having undercut sides.Flooding triggered the formation of sinkholes by saturating and liquefying overburden, which caused soil arches to collapse and flow into cavities in bedrock. The prevalence of sinkholes near the periphery of flooding suggests that drainage and loss of buoyant support as flood waters subsided may also have contributed to failure. A volume ratio index is used to quantify the three dimensional geometric form of sinkholes. Initially, small cylindrical shafts open over a bedrock joint, followed by progressive slumping that leads to widening and increases in volume to a final bowl form. Estimates of the aggregate volume of overburden transported underground in flooded areas range from 7,990 to 11,130 m3. Averaged over flooded areas, this accounts for 0.26 to 0.37 mm/km2 lowering of the surface. Based on a 500 year recurrence interval for the flood event, values for lowering of the surface range from 0.52 to 0.74 mm per 1,000 years. These values are an order of magnitude less than estimates of carbonate dissolution and suggest that transport of overburden underground is limited by triggering events. 相似文献
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Two main volcanic events are distinguished between Saraykent and Akçakışla in the Yozgat province of central Anatolia: (1) early Late Cretaceous–Palaeocene effusive activity, that produced a sequence of intermediate to felsic ‘basal lavas’; and (2) marginally later Palaeocene explosive activity that formed a series of covering ignimbrite flows. Due to their close temporal and spatial relation, geochemical comparisons were made between the silicic members of the lavas and ignimbrites, to identify chemical groups and their relative petrogenesis. The basal lavas range from calc‐alkaline basaltic andesites to dominant rhyolites. Based on trace element correlations three main geochemical groups were identified: the Akçakışla rhyolites (present as domes); Akçakışla rhyodacites‐dacites (lava flows); and Ozan‐Saraykent rhyolites (lava flows). Large‐ion lithophile elements have been mobile in all the groups, but mainly in the Akçakışla rhyolites. Rare earth element (REE) patterns show marked similarity between the Ozan and Saraykent basal lavas. The Akçakışla dome rhyolites are more fractionated with lower LaN/YbN ratios (c.10), whereas the Akçakışla basal lavas have much higher LaN/YbN ratios (c.30). The chemical coherence and petrographic similarities between the Saraykent and Ozan lavas suggest a single suite related via fractionation. Three geochemical groups were also established for the ignimbrites: Saraykent ignimbrite; Bağlıca ignimbrite‐Toklu‐Kızıldağ crystal tuffs; and Keklikpınar ignimbrite. The ignimbrites, like the basal lavas, display a pronounced depletion in Ba on ORG‐normalized plots. Relative to the basal lavas, chondrite‐normalized patterns for the ignimbrites are different in displaying negative Eu anomalies that indicate feldspar fractionation. The lack of geochemical overlap or coherence between any of the lava and ignimbrite groups suggests that they represent distinct eruptive events and are not related in any simple volcanic development and cogenetic sense. Two geochemical features are common to all the volcanic rock groups: (1) the presence of a Nb‐Ta anomaly, which is generally accepted as a crustal signature; and (2) the relatively low Y abundances which appear characteristic for the region as a whole. These fundamental features of the local silicic volcanism largely reflect source composition and effects. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
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Christine Lane Michael Haslam Michael Petraglia Peter Ditchfield Victoria Smith Ravi Korisettar 《Quaternary Science Reviews》2011,30(15-16):1819-1824
The ~74 ka BP Youngest Toba Tuff (YTT), from the largest known Quaternary volcanic eruption, has been found for the first time as a non-visible (crypto-) tephra layer within the Billa Surgam caves, southern India. The occurrence of the YTT layer in Charnel House Cave provides the first calendrical age estimate for this much debated Pleistocene faunal sequence and demonstrates the first successful application of cryptotephrochronology within a cave sequence. The YTT layer lies ~50 cm below a major sedimentological change, which is related to global cooling around the MIS 5 to MIS 4 transition. Using this isochronous event layer the Billa Surgam Cave record can be directly correlated with other archaeological sites in peninsular India and palaeoenvironmental archives across southern Asia. 相似文献
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Mulamba Teddy Bacopoulos Peter Kubatko Ethan J. Pinto Gerard F. 《Climatic change》2019,152(3-4):533-550
Climatic Change - Salinity response to sea-level rise is evaluated for a low-gradient, tidally active estuary, the lower St. Johns River, Florida. A high-resolution numerical model is forced by... 相似文献