共查询到20条相似文献，搜索用时 15 毫秒
1.
R.I. Waller A.J. Russell T.A.G.P. van Dijk & Ó. Knudsen 《Geografiska Annaler: Series A, Physical Geography》2001,83(1-2):29-38
During the initial stages of the November 1996 jökulhlaup at Skeiðarárjökull, Iceland, floodwaters burst onto the glacier surface via a series of fractures. This supraglacial drainage led to the formation of a number of distinct ice surface depressions, one of which is investigated in detail. The morphology and structural characteristics of this feature are described, as well as the sedimentology of an associated assemblage of debris-filled fractures. This work suggests that debris-charged subglacial floodwaters travelled up to the glacier surface, where supraglacial flow occurred initially via an extensive network of fractures, orientated parallel to the glacier margin. Supraglacial discharge became progressively more focused into a series of discrete outlets, leading to the mechanical erosion of a number of depressions on the glacier surface. The associated transfer of subglacially derived floodwaters to high levels within the glacier resulted in the rapid entrainment of large volumes of sediment which may influence the patterns, processes and products of ice-marginal sedimentation in the future. 相似文献
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Elisabeth Kastellet Atle Nesje & Einar Solheim Pedersen 《Geografiska Annaler: Series A, Physical Geography》1998,80(1):51-65
Documentary data provide long time series and sometimes high-resolution, detailed data from historical times to the present and can give valuable information about palaeoclimate, and for the prediction of future climates. In this paper, documentary data containing qualitative information on climate, in the form of a diary written by the farmer I.G. Grude, and two newspapers, were used for the reconstruction of the palaeoclimate at Jæren, in the county of Rogaland, in southwestern Norway, during the period 1821–50. An index method to quantify the qualitative climate data was developed and used for a low-resolution reconstruction of winter, summer and annual temperatures. A high-resolution climate reconstruction of temperature and precipitation for the winter of 1837/38 is also presented, making use of a method that keeps the climate data in a qualitative form. The climate reconstructions are compared to an instrumental temperature series from Bergen, for the same period. The two data sets are in good agreement except for summer temperature (annual temperature: r = 0.75, winter temperature: r = 0.77, summer temperature: r = 0.44). Compared to average temperatures during 1961–90, the instrumental data from Bergen during the 1821–50 period show slightly different temperatures: annual average was 0.3°C lower, winter 0.4°C lower, and summer 0.1°C lower than at present, implying conditions consistent with the "Little Ice Age" climate. 相似文献
4.
Audrey Kobayashi 《The Professional geographer》1994,46(1):73-80
My experiences combining research and activism within the Japanese-Canadian community reflect a growing concern among feminist and anti-racist scholars with the politics of work among people marginalized by racism and sexism. This concern arises within a context where “other voices” are being heard, but the legitimacy of one individual or group to represent another is being challenged. Such challenges require that essentialism and naturalism be addressed politically and theoretically, a difficult irony given the need to utilize essentialist categories to address the oppressive conditions under which they emerged. To do so, a critical theory of political construction is required. 相似文献
5.
Iréne Malmsten & Kurt Boström 《Geografiska Annaler: Series A, Physical Geography》2002,84(3&4):245-259
The Kärkejokk (jokk = Lappish for brook) is rich in sulfate and calcium, both elements having been considered enigmatic. To resolve these problems we collected waters at 13 sites during 27 June to 1 September 1996. Nine sites were in the Kärkevagge, and the others in the drainage towards lake Torne Träsk. Rain waters were collected the same period. Conductivity, pH, and temperature were measured in the field, whereas salt load and the elements Na, K, Ca, Mg, S, Si, Fe, Al, Mn, Zn, Sr, and Ba were determined in the laboratory.
Mixing models based on rain water and leaching products of the major bedrocks do not explain observed element patterns except in the lower parts of the jokk. However, oxidation of pyrite has formed acid, sulfate–rich solutions that released Ca and Mg from limestones, and Fe, Mn, Al, and Si, from black shales (Malmsten 1998; Malmsten et al. 2000). Conservative mixing models, using rain water, leached bedrock and pyrite, match the jokk waters quite well, and sulfur isotope data corroborate these findings. The nearby Låktajokk, and Vassijokk also contain much S.
Where these waters debouch they may deposit Si, Al, and Ca, but only little S on various rocks. Total rock analyses, thermodynamic and X–ray data suggest that gypsum, barite, or alunite are not formed in major quantities.
These models show that the hydrogeochemistry of the Kärkejokk may be less enigmatic than often assumed. 相似文献
Mixing models based on rain water and leaching products of the major bedrocks do not explain observed element patterns except in the lower parts of the jokk. However, oxidation of pyrite has formed acid, sulfate–rich solutions that released Ca and Mg from limestones, and Fe, Mn, Al, and Si, from black shales (Malmsten 1998; Malmsten et al. 2000). Conservative mixing models, using rain water, leached bedrock and pyrite, match the jokk waters quite well, and sulfur isotope data corroborate these findings. The nearby Låktajokk, and Vassijokk also contain much S.
Where these waters debouch they may deposit Si, Al, and Ca, but only little S on various rocks. Total rock analyses, thermodynamic and X–ray data suggest that gypsum, barite, or alunite are not formed in major quantities.
These models show that the hydrogeochemistry of the Kärkejokk may be less enigmatic than often assumed. 相似文献
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Both ‘tanka’ and ‘beri’, the well-like structures made for storing drinking water fetched from distant places or superficially charged from the runoff water of the monsoon rains, are considered integral components of rural communities in the Thar Desert of Rajasthan State in north-western India.A. stephensi, the confirmed malaria vector in desert regions, breeds in these structures predominantly. 相似文献
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Terje Brinck Løyning 《Polar research》2001,20(1):1-11
CTD profiles from the north–western Barents August 1996, have been analysed and characteristics of have been compared with former analyses and investigations The barotropic and baroclinic modes of the Rossby radius of deformation have been estimated in order to give an estimate in order to give an estimate of the spatial scale of variations. The first baroclinic mode of the Rossby radius of deformation is estimated to be around 3 km. Cold halocline water (CHW) is found in the southern part of the investigation area, supporting a hypothesis that the production of CHW is located in the area around Storbanken, and not closer to the shelf break further north. Another hypothesis is proposed: tidal induced horizontal circulation and vertical currents may explain a northward transport of warmer water across sills and banks in the north–western Barents Sea. 相似文献
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Iréne Malmsten & Kurt Boström 《Geografiska Annaler: Series A, Physical Geography》2002,84(3-4):245-259
The Kärkejokk (jokk = Lappish for brook) is rich in sulfate and calcium, both elements having been considered enigmatic. To resolve these problems we collected waters at 13 sites during 27 June to 1 September 1996. Nine sites were in the Kärkevagge, and the others in the drainage towards lake Torne Träsk. Rain waters were collected the same period. Conductivity, pH, and temperature were measured in the field, whereas salt load and the elements Na, K, Ca, Mg, S, Si, Fe, Al, Mn, Zn, Sr, and Ba were determined in the laboratory.
Mixing models based on rain water and leaching products of the major bedrocks do not explain observed element patterns except in the lower parts of the jokk. However, oxidation of pyrite has formed acid, sulfate–rich solutions that released Ca and Mg from limestones, and Fe, Mn, Al, and Si, from black shales (Malmsten 1998; Malmsten et al. 2000). Conservative mixing models, using rain water, leached bedrock and pyrite, match the jokk waters quite well, and sulfur isotope data corroborate these findings. The nearby Låktajokk, and Vassijokk also contain much S.
Where these waters debouch they may deposit Si, Al, and Ca, but only little S on various rocks. Total rock analyses, thermodynamic and X–ray data suggest that gypsum, barite, or alunite are not formed in major quantities.
These models show that the hydrogeochemistry of the Kärkejokk may be less enigmatic than often assumed. 相似文献
Mixing models based on rain water and leaching products of the major bedrocks do not explain observed element patterns except in the lower parts of the jokk. However, oxidation of pyrite has formed acid, sulfate–rich solutions that released Ca and Mg from limestones, and Fe, Mn, Al, and Si, from black shales (Malmsten 1998; Malmsten et al. 2000). Conservative mixing models, using rain water, leached bedrock and pyrite, match the jokk waters quite well, and sulfur isotope data corroborate these findings. The nearby Låktajokk, and Vassijokk also contain much S.
Where these waters debouch they may deposit Si, Al, and Ca, but only little S on various rocks. Total rock analyses, thermodynamic and X–ray data suggest that gypsum, barite, or alunite are not formed in major quantities.
These models show that the hydrogeochemistry of the Kärkejokk may be less enigmatic than often assumed. 相似文献
9.
John F. Lindsay 《Basin Research》2002,14(2):207-223
Neoproterozoic sedimentary basins cover a large area of central Australia. They rest upon rigid continental crust that varies from c. 40–50 km in thickness. Whilst the crust was in part formed during the Archaean and early Palaeoproterozoic, its final assembly occurred at approximately 1.1 Ga as the Neoproterozoic supercontinent, Rodinia, came into being. The assembly process left an indelible imprint on the region producing a strong crustal fabric in the form of a series of north dipping thrusts that pervade much of the thick craton and extend almost to the Moho. Following a period of stability (1.1–0.8 Ga), a large area of central Australia, in excess of 2.5 × 106 km2, began to subside in synchroneity. This major event was due to mantle instability resulting from the insulating effect of Rodinia. Initially, beginning c. 900 Ma, a rising superplume uplifted much of central Australia leading to peneplanation of the uplifted region and the generation of large volumes of sand‐sized clastic materials. Ultimately, the decline of the superplume led to thermal recovery and the development of a sag basin (beginning at c. 800 Ma), which in turn resulted in the redistribution of the clastic sediments and the development of a vast sand sheet at the base of the Neoproterozoic succession. The superbasin generated by the thermal recovery was short lived (c. 20 M.y.) but, in conjunction with the crustal fabric developed during supercontinent assembly, it set the stage for further long‐term basin development that extended for half a billion years well into the Late Palaeozoic. Following the sag phase at least five major tectonic episodes influenced the central Australian region. Compressional tectonics reactivated earlier thrust faults that had remained dormant within the crust, disrupting the superbasin, causing uplift of basement blocks and breaking the superbasin into the four basins now identified within the central Australian Neoproterozoic succession (Officer, Amadeus, Ngalia and Georgina Basin). These subsequent tectonic events produced the distinctive foreland architecture associated with the basins and were perhaps the trigger for the Neoproterozoic ice ages. The reactivated basins became asymmetric with major thrust faults along one margin paralleled by deep narrow troughs that formed the main depocentres for the remaining life of the basins. The final major tectonic event to influence the central Australian basins, the Alice Springs Orogeny, effectively terminated sedimentation in the region in the Late Palaeozoic (c. 290 Ma). Of the six tectonic episodes recorded in the basinal succession only one provides evidence of extension, suggesting the breakup of east Gondwana at the end of the Rodinian supercontinent cycle may have occurred at close to the time of the Precambrian–Cambrian boundary. The central Australian basins are thus the products of events surrounding the assembly and dispersal of Rodinia. 相似文献
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Theofilos Toulkeridis Norbert Clauer Sam Chaudhuri & Steve L. Goldstein 《Basin Research》1998,10(2):261-270
Isotopic determinations (K–Ar, Rb–Sr and Sm–Nd), and trace and rare-earth elemental analyses were made on a few biotite and clay fractions of Palaeozoic bentonite units from the eastern United States. The clay fractions were gently leached with dilute hydrochloric acid to study separately the acid-soluble minerals intimately associated with the extracted clay particles. The data highlight interesting potentials for this integrated approach to decipher complex tectonothermal evolutions of sedimentary basins. Biotite K–Ar ages are consistent with a Middle Ordovician stratigraphic age for the bentonite units with a mean age of 459±10 Ma. The clay residues give a Sm–Nd isochron age of 397±44 Ma, indicative of their crystallization during Acadian tectonothermal activity at about 200 °C. The clay leachates, which are considered to represent mineral phases different from clay material, yield a distinct Sm–Nd isochron age of 285±18 Ma which is indistinguishable from K–Ar ages obtained previously on the clays, suggesting a thermally induced diffusion of radiogenic 40Ar from clay particles during Alleghenian–Ouachita orogenic activity. The Rb–Sr system of the clay material seems to have been variably disturbed, except for the sample taken near the Allegheny Front for which an age of 179±4 Ma suggests a further localized activity of the thrust system at about 130–150 °C. Clearly the limited number of samples does not allow us to perfectly constrain an evolutionary model. However, analysis of the soluble minerals for their contents in metal and rare-earth elements suggests that metal-carrying fluids migrated during the Alleghenian–Ouachita orogenic activity in the eastern North American continent. Consequently, they could have contributed to the concentration of ore deposits in the region, but this possibility needs to be tested with a larger data base. 相似文献
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Michael Roche 《New Zealand geographer》2017,73(1):35-44
The article suggests Jobberns’ view of geopolitics ultimately rested on the work of British geographer Sir Halford Mackinder overlain by the writing of American political geographers. Jobberns’ geopolitical thinking was, however, also strongly informed by his being a Freemason. WWII, as the overshadowing external event of Jobberns’ early years at Canterbury, amplified his interest in geopolitics both as a way of understanding the world and, at a time when geography was not universally accepted as a university discipline, as a means of promoting to a wider public the utility of a geographical perspective on world affairs. 相似文献
15.
Jan Lundqvist 《Geografiska Annaler: Series A, Physical Geography》2003,85(1):73-89
The downwasting of the Weichselian ice sheet in the Klarälven valley and its continuation southwards has been studied. The meltwater drainage below the highest coastline (HCL) on the plain of Lake Vänern took place subglacially causing breaking‐up and calving around tunnel mouths in the ice margin. When the ice margin reached into the extension of the Klarälven valley, the drainage pattern changed to lateral. The ice disappeared as a narrow ice tongue later than in the surrounding highland. When the tongue receded northwards it left dead‐ice bodies behind, that remained in the valley after the general retreat. Along the tongue and dead‐ice bodies glaciofluvial sediments accumulated as kame terraces, deriving from esker trains in tributary valleys. At the mouths of the tributaries, deltas were deposited. Halts in the retreat occurred at a few places marked by thresholds of till. According to the present study the HCL rises northwards, from 180 m a.s.l. at Brattforsheden to 228 m at Höljes 170 km to the north. At halts in the ice recession it dropped a few metres. A tentative dating based on the level of the HCL, the tilt of raised shorelines and the rate of shoreline regression has given the time 10900 to 10360 calibrated years BP for the retreat of the ice margin from Brattforsheden to Höljes. 相似文献
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Daniel Z. Sui 《The Professional geographer》2004,56(1):62-72
Geographic information systems (GIS) and cartography have traditionally been regarded as fields for the study of techniques. Yet the past ten years have witnessed geographers' increasing intellectual engagement with GIS and cartography. This essay recaps the recent intellectual discourses on GIS and cartography and speculates on possible development in the near future. Geocomputation, spatially integrated social sciences, social informatics, information ecology, and humanistic GIScience are identified as five areas of intensive new research, and it is argued that creative imaginations under the milieu of the “third culture” are urgently needed to address the challenging issues in this new technological era. Whether geography will become an intellectually more vibrant discipline hinges on the extent to which we can rekindle geographic imaginations in this computer age via GIScience to address issues of great societal concern. 相似文献
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JONAS ÅKERMAN 《Polar research》1983,1(2):161-170
The distribution of vascular plants within four sample areas on a deflation surface on a set of raised beach ridges near Kapp Linné. Spitsbergen, is described. The vegetation cover and distribution of the different species are related to the wind pattern and microtopography. Details of the distribution and growth characteristics of Dryas octopetala, Saxifraga oppositifolia , and Silene acaulis in relation to each other, and to the wind and microtopography are discussed. 相似文献
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Supported by MSS images in the mid and late 1970s, TM images in the early 1990s and TM/ETM images in 2004, grassland degradation in the “Three-River Headwaters” region (TRH region) was interpreted through analysis on RS images in two time series, then the spatial and temporal characteristics of grassland degradation in the TRH region were ana-lyzed since the 1970s. The results showed that grassland degradation in the TRH region was a continuous change process which had large affected area and long time scale, and rapidly strengthen phenomenon did not exist in the 1990s as a whole. Grassland degradation pattern in the TRH region took shape initially in the mid and late 1970s. Since the 1970s, this deg-radation process has taken place continuously, obviously characterizing different rules in different regions. In humid and semi-humid meadow region, grassland firstly fragmentized, then vegetation coverage decreased continuously, and finally “black-soil-patch” degraded grassland was formed. But in semi-arid and arid steppe region, the vegetation coverage de-creased continuously, and finally desertification was formed. Because grassland degradation had obviously regional differences in the TRH region, it could be regionalized into 7 zones, and each zone had different characteristics in type, grade, scale and time process of grass-land degradation. 相似文献