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Judy Ehlen 《地球表面变化过程与地形》1992,17(1):53-67
The granite tors of Dartmoor are characterized by using the regional spatial patterns of 21 geomorphic, petrographic, and structural variables. The data were derived from topographic maps, field measurement, and laboratory analysis of rock samples collected in the field. Identification of spatial patterns and comparison of patterns between variables were made on contour maps generated from the data using ARC/INFO. Three tor types—summit tors, valleyside tors, and spur tors—are semiquantitatively characterized using these data and procedures. The three types of tors are distinguished with respect to variations in relative relief, joint spacing and joint type, rock texture, grain size, and composition. Summit tors have the highest relative relief (mean: 125·7 m), contain the most potassium feldspar (>30 per cent), and have the most widely-spaced primary vertical (>300 cm) and secondary horizontal joints (> 10 cm). The rocks are the most megacrystic (> 15 per cent) and the coarsest grained. Plagioclase is also abundant in summit tors. Valleyside tors have the lowest relative relief (mean: 72·9 m) and the most widely-spaced horizontal joints (primary, 60-200 cm; secondary, > 10 cm). Grain size, vertical joint spacing, and quartz and potassium feldspar abundances are intermediate. The shapes of valleyside tors are controlled by horizontal joints and the rocks are either very feebly magcrystic or equigranular in texture. Spur tors have intermediate relative relief (mean: 115·4 m), the narrowest joint spacing (vertical joints, < 200 cm, 50-75 cm; horizontal joints <60 cm, < 10 cm) and the finest grain. In addition, the rocks are feebly magacrystic. 相似文献
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H.P. Jarvie P.M. Haygarth C. Neal P. Butler B. Smith P.S. Naden A. Joynes M. Neal H. Wickham L. Armstrong S. Harman E.J. Palmer-Felgate 《Journal of Hydrology》2008,350(3-4):215-231
This study examined stream water quality across a range of catchments which are representative of the key environments and land uses of rural south-west England. These catchments included: (a) an acidic upland headwater catchment, rising on the moorlands of Dartmoor, with low-intensity sheep rearing; (b) a headwater catchment rising on the weathered granite lower slopes of Dartmoor, with cattle farming; (c) a lowland headwater clay catchment with sub-surface drainage and high intensity livestock farming, fodder crop cultivation, and hard-standing/slurry storage; and (d) the main River Taw, a lowland river system receiving drainage from a range of tributaries, exemplified by the above catchment types. Variations in water chemistry and quality were observed along an upland–lowland transition, from headwater streams to the main river channel. Within the livestock-dominated headwater streams, total phosphorus (TP) was dominated by particulate phosphorus (PP). These PP concentrations appeared to be mainly linked to two sets of processes: (1) in-stream sediment precipitation with sorption/co-precipitation of phosphate and/or localised in-channel mobilisation of sediment (by cattle or channel-clearing operations) under low flow conditions, and (2) sediment erosion and transportation associated with near-surface runoff during storm events. Under baseflow conditions, in-stream and/or riparian processes played a significant role in controlling general nutrient chemistry, particularly in the headwater streams which were heavily impacted by livestock. 相似文献
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The chronology and the hydrometeorology of catastrophic floods on Dartmoor,South West England 
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下载免费PDF全文 Extreme floods are the most widespread and often the most fatal type of natural hazard experienced in Europe, particularly in upland and mountainous areas. These ‘flash flood’ type events are particularly dangerous because extreme rainfall totals in a short space of time can lead to very high flow velocities and little or no time for flood warning. Given the danger posed by extreme floods, there are concerns that catastrophic hydrometeorological events could become more frequent in a warming world. However, analysis of longer term flood frequency is often limited by the use of short instrumental flow records (last 30–40 years) that do not adequately cover alternating flood‐rich and flood‐poor periods over the last 2 to 3 centuries. In contrast, this research extends the upland flood series of South West England (Dartmoor) back to ca AD 1800 using lichenometry. Results show that the period 1820 to mid‐1940s was characterized by widespread flooding, with particularly large and frequent events in the mid‐to‐late 19th and early 20th centuries. Since ca 1850 to 1900, there has been a general decline in flood magnitude that was particularly marked after the 1930s/mid‐1940s. Local meteorological records show that: (1) historical flood‐rich periods on Dartmoor were associated with high annual, seasonal and daily rainfall totals in the last quarter of the 19th century and between 1910 and 1946, related to sub‐decadal variability of the North Atlantic Oscillation and receipt of cyclonic and southerly weather types over the southwest peninsula; and (2) the incidence of heavy daily rainfall declined notably after 1946, similar to sedimentary archives of flooding. The peak period of flooding on Dartmoor predates the beginning of gauged flow records, which has practical implications for understanding and managing flood risk on rivers that drain Dartmoor. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
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The majority of geomorphological papers about Dartmoor have been essentially speculative, particularly when discussing weathering processes and the evolution of the Dartmoor landscape. In contrast, this article presents a synthesis of several experimental investigations aimed at studying the chemical weathering of Dartmoor granite through the systematic analysis of soil and water samples. This involved the computation of a geochemical budget to determine the amount of erosion in the catchment, as well as more detailed mineralogical investigations within a soil profile. The annual output of solutes due to weathering was 116 kg ha?1 a?1 of which the majority was silica (93 kg ha?1 a?1). From an examination of the soil mineralogy, it was calculated that these solutes were derived from the dissolution of approximately 200 kg ha?1 a?1 plagioclase, 90 kg ha?1 a?1 biotite, and 40 kg ha?1 a?1 orthoclase. As well as the weathering of granite, there was also the production of kaolinite (150 kg ha?1 a?1) and gibbsite (0.02 kg ha?1 a?1). Analysis of the soil water chemistry confirmed that kaolinite was the stable mineral phase in the regolith, although in areas where interflow was the dominant mode of water movement, the solute composition was in equilibrium with both kaolinite and gibbsite. Examination of the clay mineralogy confirmed these results. The microtexture of quartz grains was examined by the scanning electron microscope as another means of investigating the hydrochemical environment in the soil. Silica was found precipitated on all the grains examined but the maximum amount occurred in the Bs horizon. This evidence showed that, firstly, the dissolution of aluminosilicate minerals is greater than that calculated by the chemical budget and, secondly, that models of granite weathering must take localized weathering in the soil profile into account. The final part of the paper highlights the limitations of calculating denudation rates for an entire catchment and stresses the need to consider weathering as a highly localized phenomenon, particularly where there are high volumes of interflow at hill crest sites. Observations on granite decomposition in the future should be quantitative in approach and be related to the local site conditions. 相似文献
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